From 4d752ef67cfebccf22417da9e47e2e94e14c9687 Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Fri, 4 Sep 2026 15:25:40 +0100
Subject: [PATCH 1/7] Added initial draft of globals and errno

---
 errno.asm   | 24 ++++++++++++++++++++++++
 globals.asm | 18 ++++++++++++++++++
 start.asm   |  4 ++++
 3 files changed, 46 insertions(+)
 create mode 100755 errno.asm
 create mode 100755 globals.asm
 create mode 100755 start.asm

diff --git a/errno.asm b/errno.asm
new file mode 100755
index 0000000..6f2bfb3
--- /dev/null
+++ b/errno.asm
@@ -0,0 +1,24 @@
+; Error numbers should be 16 bit ODD numbers, so they can be loaded as immediates
+; and can be checked with:
+;
+;   qcall falible_function
+;   jne falible_ok ; Jump no error
+;       ; handle error
+;   falible_ok:
+;   ; Happy path
+;   ; ...
+; OR
+;   qcall falible_function
+;   je handle_error ; Jump if error
+;   ; Happy path
+;   ; ...
+;   handle_error:
+;       ; handle error
+
+pub const OK                   = 0x0000
+pub const SCREEN_INVALID_MODE  = 0x0001
+pub const SCREEN_INVALID_WIDTH = 0x0003
+pub const SCREEN_FB_TOO_SMALL  = 0x0005
+
+; Extended error codes, these would require loading a 32 bit value.
+pub const EXT_OK              = 0x00000000
\ No newline at end of file
diff --git a/globals.asm b/globals.asm
new file mode 100755
index 0000000..9dc0df4
--- /dev/null
+++ b/globals.asm
@@ -0,0 +1,18 @@
+; Addresses of global variables
+
+; If not double buffering these point to the same buffer
+pub const FB_DISPLAY_PTR     = 16 ; U32 Currently displayed buffer
+pub const FB_DRAW_PTR        = 20 ; U32 Draw to this buffer
+pub const FRAME_BUFFER_SIZE  = 24 ; U32
+pub const PIXEL_WIDTH        = 28 ; U16
+pub const PIXEL_HEIGHT       = 30 ; U16
+
+; Log2 of width in pixels, e.g.
+; * 10 => 1024 * 768
+pub const LOG_WIDTH          = 32 ; U8
+
+pub const BYTES_PER_PIXEL    = 33 ; U8
+; Log2 of bytes per pixel
+; * 0 => 8 bits per pixel
+; * 2 => 32 bits per pixel
+pub const LOG_BPP            = 34 ; U8
diff --git a/start.asm b/start.asm
new file mode 100755
index 0000000..4c7f7f2
--- /dev/null
+++ b/start.asm
@@ -0,0 +1,4 @@
+@0 ; Reserve space for globals
+ 
+jmp 0x100 ; jump over them
+@0x100 ; start of user code
\ No newline at end of file
-- 
2.54.0


From 04f3f03ad5c644cc23007f111ec3c8806eefa48c Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Fri, 4 Sep 2026 16:42:35 +0100
Subject: [PATCH 2/7] Moved new *.asm files into src/ v

---
 errno.asm => src/errno.asm     | 0
 globals.asm => src/globals.asm | 0
 start.asm => src/start.asm     | 0
 3 files changed, 0 insertions(+), 0 deletions(-)
 rename errno.asm => src/errno.asm (100%)
 rename globals.asm => src/globals.asm (100%)
 rename start.asm => src/start.asm (100%)

diff --git a/errno.asm b/src/errno.asm
similarity index 100%
rename from errno.asm
rename to src/errno.asm
diff --git a/globals.asm b/src/globals.asm
similarity index 100%
rename from globals.asm
rename to src/globals.asm
diff --git a/start.asm b/src/start.asm
similarity index 100%
rename from start.asm
rename to src/start.asm
-- 
2.54.0


From 46abf8d893ad55f5e20993456360d080184bf084 Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Sun, 6 Sep 2026 11:02:27 +0100
Subject: [PATCH 3/7] Add globals and error codes

Added support for global variables.

This requires including `start.asm` as the first code. This includes
a `jmp` to 0x100 for user code, and a magic number that modules
can check to verify th the user has correctly reserved the space.

The magic number is 0xb301534c:

* This has the high bit set so is not a valid instruction

* On builds that ignore the high bit this decodes to `nor zr, zr,
  0x534c` a no-op.

* The immediate is "SL" for standardl ibrary.

Due to a bug start pads with U... 0, instead of @addr.

`start.asm` also initialises `sp` so it start just below the 64KiB LUT
memory alocation.

Added some error codes for the upcoming graphics module.
---
 CONTRIBUTING.md     |  13 +-
 README.md           |   9 +-
 src/errno.asm       |   3 +
 src/globals.asm     |  24 +-
 src/graphics_32.asm | 672 ++++++++++++++++++++++++++++++++++++++++++++
 src/start.asm       |  23 +-
 6 files changed, 730 insertions(+), 14 deletions(-)
 create mode 100644 src/graphics_32.asm

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ed897a3..f316bb3 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -16,10 +16,21 @@ All functions in the standard library should follow the following outline:
 ; Arguments: <which register contains what argument>
 ; Result: <what is the result, and where is it stored>
 ; Clobbers: <list of registers that are clobbered>
+; Globals: <list of globals are accessed. OPTIONAL>
 <label>: <;SHOULD BE INLINED>
     <CODE>
 
 ```
 
 Functions should be in the appropriate asm file, if you are unsure where functionality fits make a seperate file and ask in the pull request
-Functions that are provided for convenience/reference but should be inlined in production code should be marked with `;SHOULD BE INLINED` after their label
+Functions that are provided for convenience/reference but should be inlined in production code should be marked with `;SHOULD BE INLINED` after their label.
+
+If the function returns a status code in flags, the preamble should list all it might return.
+
+## Globals
+
+Any function that uses global variables should document this in the preamble comment, see above.
+
+A file/module should check on intialisation that the address `globals.MAGIC_ADDRESS` contains the 16 bit value `globals.MAGIC_VALUE`, to ensure that the user has properly included [[src/start.asm]] and reservered the global variable area.
+
+No opinion is offered on whether modules can assume globals variables are initialised to zero.
\ No newline at end of file
diff --git a/README.md b/README.md
index b973fa2..dcd9ff3 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 This is a standard library for symphony.
 It is both intended as a practical toolkit to develop more complex software as well as a teaching resource.
 
-If you just want to use the standard library [[src/stdlib.asm]] is your main header, include it after your code.
+If you just want to use the standard library [[src/stdlib.asm]] is your main header, include it after your code. Some modules also require [[src/start.asm]] at the very start of the program.
 
 If you are using it as a learning resource have a look at the [teaching folder](teaching).
 
@@ -20,7 +20,7 @@ If you are intersted in contributing have a look at [[CONTRIBUTING.md]]
 | preserved | sp, r8 - r12 |
 | scratch | flags, r1 - r7 |
 | arguments | r1 - r7 |
-| result | r1-r7 |
+| result | flags, r1 - r7 |
 | return address | r13 |
 
 Arguments not fitting into the 7 registers should be passed on the top of the stack, meaning they should be the last values pushed before the function call.
@@ -32,9 +32,14 @@ Should a function return more values than fit into the 7 registers, the caller h
 This reduces the amount of argument registers to 6 and all arguments above that shall go on the stack, the pointer to the result stack shall **always** be passed in an argument register.
 This register points at the highest available address for results, with the 8th result being stored there, the 9th below it and so on.
 
+Some functions return a success/failure status code in flags. A set low bit will indicate some error condition, the function may return more than one possible value to report different errors. A flags value of 0 is set on success. No other even values are used. This can be checked with `je` or `jne` immediatly on return to the caller. All other functions clobber flags.
+
 ### Stack
 Grows downwards from 0xXXFE_0000 (so top of memory -0x1_0000).
 
+### Globals
+Global variables are stored near the bottom of RAM in the address range 0x0010..0x0100. Programs should `include src/start` as the first line before their own code and before other includes, or otherwise reserve this space, the first instruction should be a jump to user code.
+
 ### Types
 
 #### String
diff --git a/src/errno.asm b/src/errno.asm
index 6f2bfb3..5d06c89 100755
--- a/src/errno.asm
+++ b/src/errno.asm
@@ -19,6 +19,9 @@ pub const OK                   = 0x0000
 pub const SCREEN_INVALID_MODE  = 0x0001
 pub const SCREEN_INVALID_WIDTH = 0x0003
 pub const SCREEN_FB_TOO_SMALL  = 0x0005
+pub const SCREEN_OUTSIDE_FB    = 0x0007
+
+pub const MAGIC_BAD            = 0x8001
 
 ; Extended error codes, these would require loading a 32 bit value.
 pub const EXT_OK              = 0x00000000
\ No newline at end of file
diff --git a/src/globals.asm b/src/globals.asm
index 9dc0df4..fa38ae2 100755
--- a/src/globals.asm
+++ b/src/globals.asm
@@ -1,18 +1,28 @@
 ; Addresses of global variables
 
 ; If not double buffering these point to the same buffer
+; If double buffering they must the same size
 pub const FB_DISPLAY_PTR     = 16 ; U32 Currently displayed buffer
-pub const FB_DRAW_PTR        = 20 ; U32 Draw to this buffer
-pub const FRAME_BUFFER_SIZE  = 24 ; U32
-pub const PIXEL_WIDTH        = 28 ; U16
-pub const PIXEL_HEIGHT       = 30 ; U16
+pub const FB_DISPLAY_STRIDE  = 20 ; U32 Bytes in each row of the displayed buffer
+pub const FB_DRAW_PTR        = 24 ; U32 Draw to this buffer
+pub const FB_DRAW_STRIDE     = 28 ; U32 Bytes in each row of the draw buffer
+pub const FB_SIZE_BYTE       = 32 ; U32 In bytes
+pub const FB_WIDTH_PX        = 36 ; U16 Width of screen in pixels
+pub const FB_HEIGHT_PX       = 38 ; U16 Height of screen in pixels
 
 ; Log2 of width in pixels, e.g.
 ; * 10 => 1024 * 768
-pub const LOG_WIDTH          = 32 ; U8
+; *  8 =>  256 * 192
+pub const FB_LOG_WIDTH       = 40 ; U8
+pub const FB_LOG_STRIDE      = 41 ; U8 Log2 of FB_xxx_STRIDE in bytes
 
-pub const BYTES_PER_PIXEL    = 33 ; U8
+pub const FB_BYTES_PER_PIXEL = 42 ; U8 Specialisations should hardcode this
 ; Log2 of bytes per pixel
 ; * 0 => 8 bits per pixel
 ; * 2 => 32 bits per pixel
-pub const LOG_BPP            = 34 ; U8
+pub const FB_LOG_BPP         = 43 ; U8 Specialisations should hardcode this
+
+pub const MAGIC_ADDRESS_LONG = 12 ; U32 Location of the magic value
+pub const MAGIC_VALUE_LONG   = 0xb301534c ; U32 Full 32 bits of the magic value
+pub const MAGIC_ADDRESS      = 14 ; U16 Location of the low 16 bits of magic value
+pub const MAGIC_VALUE        = 0x534c ; U16 Low 16 bits of the magic value
diff --git a/src/graphics_32.asm b/src/graphics_32.asm
new file mode 100644
index 0000000..ad1832b
--- /dev/null
+++ b/src/graphics_32.asm
@@ -0,0 +1,672 @@
+; 32 bit graphics library for Symphony
+
+include globals
+include errno
+
+const SCREEN_SETTING_MODE             = 0 ; Use zr instead
+const SCREEN_SETTING_DATA_OFFSET      = 1
+const SCREEN_SETTING_RESOLUTION       = 2
+const SCREEN_SETTING_FOREGROUND_COLOR = 2
+const SCREEN_SETTING_BACKGROUND_COLOR = 3
+const SCREEN_SETTING_FONT             = 4
+
+const SCREEN_MODE_TEXT_8         = 0
+const SCREEN_MODE_TEXT_32        = 1
+const SCREEN_MODE_GRAPHICS_8     = 2
+const SCREEN_MODE_GRAPHICS_32    = 3
+
+pub set_graphics_mode:
+; u16 set_graphics_mode(void *FB_ptr, size_t FB_size, u8 bit_per_pixel, u16 width, bool clear, bool double_buf)
+; Sets the screen to graphics mode, the resolution, and colour depth.
+; Optionally clears the screen.
+;
+; Arguments:
+; - r1: Point to allocated framebuffer
+; - r2: Size of FB allocation, in bytes
+; - r3: Bits per pixel: One of `8` or `32`
+; - r4: Width - height is set to `width / 4 * 3`
+; - r5: If non-zero, clears the current framebuffer.
+; - r6: If non-zero, enable double buffering
+; Returns:
+; - r1: Status
+;   * 0 OK
+;   * SCREEN_INVALID_SIZE width invalid
+;   * SCREEN_INVALID_MODE bits_per_pixel invalid
+;   * SCREEN_FB_TOO_SMALL allocation too small
+; Clobbers:
+; - r2-r6, flags
+; Globals written:
+; - LOG_STRIDE
+; - FB_WIDTH
+; - FB_HEIGHT
+; - BITS_PER_PIXEL
+
+    ; Check the magic number
+    load_16 flags, [globals.MAGIC_ADDRESS]
+    cmp flags, globals.MAGIC_VALUE
+    je set_graphics_mode_magic_ok
+        mov flags, errno.MAGIC_BAD
+        jmp r13 ; return
+    set_graphics_mode_magic_ok:
+
+    push r8 ; LOG Bytes/pixel
+    push r9 ; Log width
+    push r10 ; Height
+    push r11 ; Size of FB in bytes/pixels
+    
+    cmp r3, 32
+    jne not_32_bit_mode
+    mov r3, SCREEN_MODE_GRAPHICS_32
+    mov r8, 2
+    jmp mode_ok
+    
+    not_32_bit_mode:
+    cmp r3, 8
+    jne invalid_mode
+    mov r3, SCREEN_MODE_GRAPHICS_8
+    mov r8, 0
+    jmp mode_ok
+    
+    invalid_mode: 
+        pop r11
+        pop r10
+        pop r9
+        pop r8
+        mov flags, errno.SCREEN_INVALID_MODE
+        jmp r13 ; return
+    mode_ok:
+
+    ; Width must be between 4 and 1024
+    cmp r4, 1024 ; max width of screen
+    ja width_invalid
+    cmp r4, 4
+    jb width_invalid
+    ; Is width a power of two?
+    mov r9, 10
+    mov r10, 1024
+    log_width_loop:
+        cmp r4, r10
+        je width_ok
+        lsr r10, r10, 1
+        sub r9, r9, 1
+        cmp r9, 4
+        jae log_width_loop
+    width_invalid:
+        pop r11
+        pop r10
+        pop r9
+        pop r8
+        mov flags, errno.SCREEN_INVALID_WIDTH
+        jmp r13 ; return
+    width_ok:
+    ; Now r9 = log width
+    
+    
+    ; height = width/4 * 3
+    lsr r4, r4, 2
+    lsl r10, r4, 1
+    add r10, r10, r4 ; height
+    
+    ; Compute size of FB
+    lsl r11, r10, r9 ; Size of FB in pixels
+    lsl r11, r11, r8 ; Size of FB in bytes
+    ; If double buffering..
+    cmp r6, 0
+    je single_buff
+        ; ..we need twice the space
+        lsl r11, r11, 1
+    single_buff:
+    cmp r2, r11
+    jae size_ok
+        pop r11
+        pop r10
+        pop r9
+        pop r8
+        mov flags, errno.SCREEN_FB_TOO_SMALL
+        jmp r13 ; return
+    size_ok:
+
+    ; Set screen mode
+	screen zr, r3
+    ; Set screen size
+    mov flags, SCREEN_SETTING_RESOLUTION
+    ; Setting is width/4 - 1
+    sub r4, r4, 1
+    screen flags, r4
+    ; Restore width
+    add r4, r4, 1
+    lsl r4, r4, 2
+
+    ; Set FB pointer
+    ; If double buffering..
+    cmp r6, 0
+    je save_fb_single_buff
+        ; ..we want the size of each FB
+        lsr r11, r11, 1
+        store_32 [globals.FB_SIZE_BYTE], r11
+        store_32 [globals.FB_DISPLAY_PTR], r2
+        mov r3, SCREEN_SETTING_DATA_OFFSET
+        screen r3, r2
+        add r2, r2, r11
+        jmp save_fb_done
+    save_fb_single_buff:
+        store_32 [globals.FB_SIZE_BYTE], r11
+        store_32 [globals.FB_DISPLAY_PTR], r2
+        mov r3, SCREEN_SETTING_DATA_OFFSET
+        screen r3, r2
+    save_fb_done:
+    store_32 [globals.FB_DRAW_PTR], r2
+    
+    store_16 [globals.FB_WIDTH_PX], r4
+    store_16 [globals.FB_HEIGHT_PX], r10
+    store_8 [globals.FB_LOG_WIDTH], r9
+    store_8 [globals.FB_LOG_BPP], r8
+    mov flags, 1
+    lsl r8, flags, r8
+    store_8 [globals.FB_BYTES_PER_PIXEL], r8
+
+    mov r1, r2 ; Return draw FB
+	mov r3, 0
+	mov r4, 0
+    ; TODO call clear
+	nor r2, zr, 0xff ; Colour = White (32-bit)
+
+    pop r11
+    pop r10
+    pop r9
+    pop r8
+    mov flags, 0 ; OK
+	jmp r13 ; return
+
+pub set_text_mode:
+; u16 set_text_mode(void *FB_ptr, size_t FB_size, u8 bit_per_pixel, u8 font, bool clear, bool double_buf)
+; Sets the screen to text mode, the font, and colour depth. Also sets fore ground and background colors.
+; Optionally clears the screen.
+
+; Arguments:
+; - r1: Address of allocated framebuffer
+; - r2: Size of FB allocation, in bytes
+; - r3: Bits per pixel: One of `8` or `32`
+; - r4: Font, one of {0,1,2,3}
+; - r5: If non-zero, clears the current framebuffer.
+; - r6: If non-zero, enable double buffering
+; Returns:
+; - r1: Status
+;   * 0 OK
+;   * SCREEN_INVALID_SIZE width invalid
+;   * SCREEN_INVALID_MODE bits_per_pixel invalid
+;   * SCREEN_FB_TOO_SMALL allocation too small
+; Clobbers:
+; - r2-r6, flags
+; Globals written:
+; - LOG_STRIDE
+; - FB_WIDTH
+; - FB_HEIGHT
+; - BITS_PER_PIXEL
+
+    ; Check the magic number
+    load_16 flags, [globals.MAGIC_ADDRESS]
+    cmp flags, globals.MAGIC_VALUE
+    je set_text_mode_magic_ok
+        mov flags, errno.MAGIC_BAD
+        jmp r13 ; return
+    set_text_mode_magic_ok:
+
+;TODO: Sanity checks
+;TODO: ?Clear screen
+    push r8 ; LOG Bytes/pixel
+    push r9 ; Log width
+    push r10 ; Height
+    push r11 ; Size of FB in bytes/pixels
+    
+    cmp r3, 32
+    jne not_32_bit_text_mode
+    mov r3, SCREEN_MODE_TEXT_32
+    mov r8, 2
+    jmp text_mode_ok
+    
+    not_32_bit_text_mode:
+    cmp r3, 8
+    jne invalid_text_mode
+    mov r3, SCREEN_MODE_TEXT_8
+    mov r8, 0
+    jmp text_mode_ok
+    
+    invalid_text_mode: 
+        pop r11
+        pop r10
+        pop r9
+        pop r8
+        mov flags, errno.SCREEN_INVALID_MODE
+        jmp r13 ; return
+    text_mode_ok:
+
+    ; Set screen mode
+	screen zr, r3
+
+    ; Set FB pointer
+    ; If double buffering..
+    cmp r6, 0
+    je save_fb_single_text_buff
+        ; ..we want the size of each FB
+        lsr r11, r11, 1
+        store_32 [globals.FB_SIZE_BYTE], r11
+        store_32 [globals.FB_DISPLAY_PTR], r2
+        mov r3, SCREEN_SETTING_DATA_OFFSET
+        screen r3, r2
+        add r2, r2, r11
+        jmp save_fb_text_done
+    save_fb_single_text_buff:
+        store_32 [globals.FB_SIZE_BYTE], r11
+        store_32 [globals.FB_DISPLAY_PTR], r2
+        mov r3, SCREEN_SETTING_DATA_OFFSET
+        screen r3, r2
+    save_fb_text_done:
+    store_32 [globals.FB_DRAW_PTR], r2
+
+    ; Set screen font
+    ; Only 0, 1, 2, 3 are valid
+    and r4, r4, 3
+    mov flags, SCREEN_SETTING_FONT
+    screen flags, r4
+
+	; Set foreground to white
+    mov flags, SCREEN_SETTING_FOREGROUND_COLOR
+	nor r4, zr, 0xff ; White    
+    screen flags, r4
+
+	; Set background to black	
+    mov flags, SCREEN_SETTING_BACKGROUND_COLOR
+	screen flags, zr
+	
+    pop r11
+    pop r10
+    pop r9
+    pop r8
+    mov flags, 0 ; OK
+	jmp r13 ; return
+
+pub set_text_mode_default:
+; u16 set_text_mode_default(void *FB_ptr)
+; Sets the screen to default text mode, the font, and colour depth. Also sets fore ground and background colors.
+; Does not clear the screen.
+; Size of allcation is not checked
+;
+; Arguments:
+; - r1: Address of allocated framebuffer
+; Returns:
+; - flags: 0 ; ok, never fails
+; Clobbers:
+; - r1, flags
+; Globals written:
+; - FB_DISPLAY_PTR
+; - FB_DRAW_PTR
+; - FRAME_BUFFER_SIZE
+
+    ; Set screen mode to default 8 bit text
+	screen zr, zr
+
+    ; Set FB pointer
+    store_32 [globals.FB_DISPLAY_PTR], r1
+    store_32 [globals.FB_DRAW_PTR], r1
+    ; Size is 96*40*1 byte
+    mov r1, 3840
+    store_32 [globals.FB_SIZE_BYTE], r1
+    mov flags, SCREEN_SETTING_DATA_OFFSET
+    screen flags, r1
+
+    ; Set default screen font
+    mov flags, SCREEN_SETTING_FONT
+    screen flags, zr
+
+	; Set foreground to white
+    mov flags, SCREEN_SETTING_FOREGROUND_COLOR
+	nor r1, zr, 0xff ; White
+    screen flags, r1
+
+	; Set background to black	
+    mov flags, SCREEN_SETTING_BACKGROUND_COLOR
+	screen flags, zr
+
+    mov flags, 0 ; OK
+    jmp r13
+
+pub clear:
+; void clear()
+; Paints the whole screen black
+;
+; Arguments:
+; - None
+; Clobbers:
+; - r1: Color
+; - r2: fill_screen
+; - r3: fill_screen
+; - r4: fill_screen
+; - flags
+
+	mov r1, 0 ; Black
+	; Fall through
+
+pub fill_screen:
+; void fill_screen(u32 color)
+; Fills the whole screen in a single color.
+;
+; Arguments:
+; - r1: Color, 32 bit RGB0
+; Clobbers:
+; - r2: Pixel pointer
+; - r3: End address
+; - r4: Stride
+; - flags
+; Reads globals:
+; - FB_DRAW_PTR
+; - LOG_BPP
+; - LOG_WIDTH
+; - PIXEL_HEIGHT
+
+	load_8 r2, [globals.FB_LOG_WIDTH]
+	load_16 r3, [globals.FB_HEIGHT_PX]
+	lsl r3, r3, r2
+	load_8 r4, [globals.FB_LOG_BPP]
+	lsl r3, r3, r4 ; Num bytes in FB
+	load_32 r2, [globals.FB_DRAW_PTR]
+	add r3, r3, r2 ; End of FB
+	load_8 r4, [globals.FB_BYTES_PER_PIXEL]
+	fill_screen_loop:
+		; Screen is always a multiple of 4*3
+		; we can unroll this 12 times.
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		store_32 [r2], r1
+		add r2, r2, r4
+		cmp r2, r3
+		jb fill_screen_loop
+
+	jmp r13 ; return
+
+
+pub switch_buffers: ; SHOULD BE INLINED
+; void switch_buffers()
+; Swaps the display and draw buffers, and updates the screen to use the new display buffer.
+;; Safe to run when single buffered.
+;
+; Arguments:
+; - None
+; Returns:
+; - None
+; Clobbers:
+; - r1: Old display FB => new draw FB
+; - r2: Old draw FB => new display FB
+; - flags
+; Globals written:
+; - FB_DISPLAY_PTR
+; - FB_DRAW_PTR
+
+    load_32 r1, [globals.FB_DISPLAY_PTR]
+    load_32 r2, [globals.FB_DRAW_PTR]
+    mov flags, SCREEN_SETTING_DATA_OFFSET
+    screen flags, r2
+    store_32 [globals.FB_DISPLAY_PTR], r2
+    store_32 [globals.FB_DRAW_PTR], r1
+    
+    jmp r13 ; return
+
+
+pub draw_pixel:
+; void draw_pixel(u32 color, u16 x, u16 y)
+; Draw pixel at the position, no checks on position, can potentally write to any memory.
+; Framebuffer pointer is stored in FB_PTR.
+;
+; Arguments:
+; - r1 Color 24 bit RGB0   PRESERVED
+; - r2 X coord             PRESERVED
+; - r3 Y coord             PRESERVED
+; - r4-r7 ignored but      PRESERVED
+; Result:
+; - None
+; Clobbers:
+; - flags
+; Globals read:
+; - FB_DRAW_PTR
+; - LOG_WIDTH
+
+    ; Screen is `1 << WIDTH pixels wide
+    load_8 flags, [globals.FB_LOG_WIDTH]
+	; Compute pixel address
+	lsl flags, r4, flags ; Y * width
+	add flags, flags, r3 ; Y * width + X
+	lsl flags, flags, 2 ; pixel to address
+    load_32 r1, [globals.FB_DRAW_PTR]
+	add flags, flags, r1 ; += frambuffer_ptr
+	; Set pixel value
+	store_32 [flags], r2
+	jmp r13 ; return
+
+
+pub draw_line_h:
+; void draw_line_h(u32 color, u16 x0, u16 y, u16 x1)
+; Draws a straight horizontal line from (x0, y) to (x1, y) (inclusive) using `color`
+; on to the current `FB_DRAW_PTR` buffer.
+;
+; Arguments:
+; - r1: Color 24 bit RGB0   PRESERVED
+; - r2: X0 coord
+; - r3: Y coord             PRESERVED
+; - r4: X1 coord
+; Returns:
+; - r1: Color 24 bit RGB0   PRESERVED
+; - r2: X1 coord
+; - r3: Y coord             PRESERVED
+; Clobbers:
+; - r7, flags
+
+	push r13
+
+	; if x0 > x1
+		; dx = -1
+	; else
+		; dx = +1
+	; endif
+	cmp r4, r2
+	or r7, flags, 0x02
+	lsl r7, r7, 29
+	asr r7, r7, 30
+
+	jmp draw_line_h_loop_in
+	draw_line_h_loop:
+		add r2, r2, r7
+	draw_line_h_loop_in:
+		qcall draw_pixel
+		cmp r2, r4
+		jne draw_line_h_loop
+
+	pop r13
+	jmp r13 ; return
+
+
+pub draw_line_v:
+; void draw_line_v(u32 color, u16 x, u16 _, u16 y0, u16 x1)
+; Draws a straight verticle line from (x, y0) to (x, y1) (inclusive) using `color`
+; on to the current `FB_DRAW_PTR` buffer.
+;
+; Arguments:
+; - r1: Color 24 bit RGB0   PRESERVED
+; - r2: X coord             PRESERVED
+; - r3: Y0 coord
+; - r4: ignored but         PRESERVED
+; - r5: Y1 coord
+
+; Returns:
+; - r1: Color 24 bit RGB0   PRESERVED
+; - r2: X coord             PRESERVED
+; - r3: Y1 coord
+; Clobbers:
+; - r7, flags
+
+	push r13
+
+	; if y0 > y1
+		; dy = -1
+	; else
+		; dy = +1
+	; endif
+	cmp r5, r3
+	or r7, flags, 0x02
+	lsl r7, r7, 29
+	asr r7, r7, 30
+
+	jmp draw_line_v_loop_in
+	draw_line_v_loop:
+		add r3, r3, r7
+	draw_line_v_loop_in:
+		qcall draw_pixel
+		cmp r3, r5
+		jne draw_line_v_loop
+
+	pop r13
+	jmp r13 ; return
+
+
+pub draw_line:
+; void draw_line(u32 color, u16 x0, u16 y0, u16 x1, u16 y1)
+; Draws a straight line from (x0, y0) to (x1, y1) (inclusive) using `color`
+; on to the current `FB_DRAW_PTR` buffer.
+;
+; Arguments:
+; - r1: Color 24 bit RGB0   PRESERVED
+; - r2: X0 coord
+; - r3: Y0 coord
+; - r4: X1 coord
+; - r5: Y1 coord
+; Returns:
+; - r1: Color 24 bit RGB0   PRESERVED
+; - r2: X1 coord
+; - r3: Y1 coord
+; Clobbers:
+; - r4-r7, flags
+; Globals read:
+; - FB_DRAW_PTR
+; - FB_DRAW_STRIDE
+; - ...others I expect
+
+;	push r11 ; sy
+;	push r10 ; dy
+;	push r9 ; sx
+;	push r8 ; dx
+
+    ; int dx = abs(x1-x0), sx = x0<x1 ? 1 : -1;
+    cmp r2, r4
+    ja draw_line_move_left
+    jb draw_line_move_right
+    ; if x0 == x1
+        jmp draw_line_v ; tail call
+    ; elif x0 < x1
+    draw_line_move_right:
+        push r8 ; dx
+        push r9 ; sx
+        sub r8, r4, r2
+        mov r9, 1
+        jmp draw_line_move_right_done
+    ; else x0 > x1
+    draw_line_move_left:
+        push r8 ; dx
+        push r9 ; sx
+        sub r8, r2, r4
+        nor r9, zr, zr ; sx = -1
+    ; endif
+    draw_line_move_right_done:
+
+    ; int dy = -abs(y1-y0), sy = y0<y1 ? 1 : -1;
+    cmp r3, r5
+    jb draw_line_move_down
+    ja draw_line_move_up
+    ; if y0 == y0
+        ; Restore r8, r9
+        pop r9
+        pop r8
+        jmp draw_line_h ; tail call
+    ; elif y0 < y1
+    draw_line_move_down:
+        push r10 ; dy
+        push r11 ; sy
+        sub r10, r3, r5
+        mov r11, 1
+        jmp draw_line_move_down_done
+    ; else y0 > y1
+    draw_line_move_up:
+        push r10 ; dy
+        push r11 ; sy
+        sub r10, r5, r3
+        nor r11, zr, zr ; sy = -1
+    ; endif
+    draw_line_move_down_done:
+
+	push r12 ; err, err2
+	push r13 ; lr
+
+    ; int err = dx+dy /* error value e_xy */
+    add r12, r8, r10
+    ; loop while(true)
+    draw_line_loop:
+     
+        qcall draw_pixel
+        ; err2 = 2*err;
+        lsl r12, r12, 1
+        ; if (err2 >= dy) { /* e_xy+e_x > 0 */
+        cmp r12, r10
+        lsr r12, r12, 1 ; restore err
+        jl draw_line_loop_skip_x
+            ; if (x0 == x1) break;
+            cmp r2, r4
+            je draw_line_loop_done
+            ; err += dy
+            add r12, r12, r10
+            ; x0 += sx;
+            add r2, r2, r9
+        draw_line_loop_skip_x:
+
+        ; err2 = 2*err;
+        lsl r12, r12, 1
+        ; if (err2 <= dx) { /* e_xy+e_y < 0 */
+        cmp r12, r8
+        lsl r12, r12, 1 ; restore err
+        jl draw_line_loop_skip_y
+            ; if (y0 == y1) break;
+            cmp r3, r5
+            je draw_line_loop_done
+            ; err += dx
+            add r12, r12, r8
+            ; y0 += sy
+            add r3, r3, r11
+        draw_line_loop_skip_y:
+	    jmp draw_line_loop
+    ; endloop
+    draw_line_loop_done:
+
+	pop r13
+	pop r12
+	pop r11
+	pop r10
+	pop r9
+	pop r8
+	jmp r13 ; return
diff --git a/src/start.asm b/src/start.asm
index 4c7f7f2..c7e108f 100755
--- a/src/start.asm
+++ b/src/start.asm
@@ -1,4 +1,19 @@
-@0 ; Reserve space for globals
- 
-jmp 0x100 ; jump over them
-@0x100 ; start of user code
\ No newline at end of file
+;@0 ; Reserve space for globals
+
+; First initialise the stack pointer
+nor sp, zr, 0xffff
+; Jump over the globals to user code
+jmp 0x100
+
+U32 0 ; 4 bytes
+
+; MAGIC_VALUE
+;@0x0c
+U32 0xb301534c
+
+; Pad with zeroes since the @addr feature is currently broken.
+; * https://discord.com/channels/828292123936948244/1545010596246847568
+;
+U1920 0  ; 240 bytes
+
+;@0x100 ; start of user code
\ No newline at end of file
-- 
2.54.0


From 21deca64fd859e8ec96e17e46f2450364ed7c8a0 Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Sun, 6 Sep 2026 15:48:37 +0100
Subject: [PATCH 4/7] Remove graphics code from this PR

---
 src/graphics_32.asm | 672 --------------------------------------------
 1 file changed, 672 deletions(-)
 delete mode 100644 src/graphics_32.asm

diff --git a/src/graphics_32.asm b/src/graphics_32.asm
deleted file mode 100644
index ad1832b..0000000
--- a/src/graphics_32.asm
+++ /dev/null
@@ -1,672 +0,0 @@
-; 32 bit graphics library for Symphony
-
-include globals
-include errno
-
-const SCREEN_SETTING_MODE             = 0 ; Use zr instead
-const SCREEN_SETTING_DATA_OFFSET      = 1
-const SCREEN_SETTING_RESOLUTION       = 2
-const SCREEN_SETTING_FOREGROUND_COLOR = 2
-const SCREEN_SETTING_BACKGROUND_COLOR = 3
-const SCREEN_SETTING_FONT             = 4
-
-const SCREEN_MODE_TEXT_8         = 0
-const SCREEN_MODE_TEXT_32        = 1
-const SCREEN_MODE_GRAPHICS_8     = 2
-const SCREEN_MODE_GRAPHICS_32    = 3
-
-pub set_graphics_mode:
-; u16 set_graphics_mode(void *FB_ptr, size_t FB_size, u8 bit_per_pixel, u16 width, bool clear, bool double_buf)
-; Sets the screen to graphics mode, the resolution, and colour depth.
-; Optionally clears the screen.
-;
-; Arguments:
-; - r1: Point to allocated framebuffer
-; - r2: Size of FB allocation, in bytes
-; - r3: Bits per pixel: One of `8` or `32`
-; - r4: Width - height is set to `width / 4 * 3`
-; - r5: If non-zero, clears the current framebuffer.
-; - r6: If non-zero, enable double buffering
-; Returns:
-; - r1: Status
-;   * 0 OK
-;   * SCREEN_INVALID_SIZE width invalid
-;   * SCREEN_INVALID_MODE bits_per_pixel invalid
-;   * SCREEN_FB_TOO_SMALL allocation too small
-; Clobbers:
-; - r2-r6, flags
-; Globals written:
-; - LOG_STRIDE
-; - FB_WIDTH
-; - FB_HEIGHT
-; - BITS_PER_PIXEL
-
-    ; Check the magic number
-    load_16 flags, [globals.MAGIC_ADDRESS]
-    cmp flags, globals.MAGIC_VALUE
-    je set_graphics_mode_magic_ok
-        mov flags, errno.MAGIC_BAD
-        jmp r13 ; return
-    set_graphics_mode_magic_ok:
-
-    push r8 ; LOG Bytes/pixel
-    push r9 ; Log width
-    push r10 ; Height
-    push r11 ; Size of FB in bytes/pixels
-    
-    cmp r3, 32
-    jne not_32_bit_mode
-    mov r3, SCREEN_MODE_GRAPHICS_32
-    mov r8, 2
-    jmp mode_ok
-    
-    not_32_bit_mode:
-    cmp r3, 8
-    jne invalid_mode
-    mov r3, SCREEN_MODE_GRAPHICS_8
-    mov r8, 0
-    jmp mode_ok
-    
-    invalid_mode: 
-        pop r11
-        pop r10
-        pop r9
-        pop r8
-        mov flags, errno.SCREEN_INVALID_MODE
-        jmp r13 ; return
-    mode_ok:
-
-    ; Width must be between 4 and 1024
-    cmp r4, 1024 ; max width of screen
-    ja width_invalid
-    cmp r4, 4
-    jb width_invalid
-    ; Is width a power of two?
-    mov r9, 10
-    mov r10, 1024
-    log_width_loop:
-        cmp r4, r10
-        je width_ok
-        lsr r10, r10, 1
-        sub r9, r9, 1
-        cmp r9, 4
-        jae log_width_loop
-    width_invalid:
-        pop r11
-        pop r10
-        pop r9
-        pop r8
-        mov flags, errno.SCREEN_INVALID_WIDTH
-        jmp r13 ; return
-    width_ok:
-    ; Now r9 = log width
-    
-    
-    ; height = width/4 * 3
-    lsr r4, r4, 2
-    lsl r10, r4, 1
-    add r10, r10, r4 ; height
-    
-    ; Compute size of FB
-    lsl r11, r10, r9 ; Size of FB in pixels
-    lsl r11, r11, r8 ; Size of FB in bytes
-    ; If double buffering..
-    cmp r6, 0
-    je single_buff
-        ; ..we need twice the space
-        lsl r11, r11, 1
-    single_buff:
-    cmp r2, r11
-    jae size_ok
-        pop r11
-        pop r10
-        pop r9
-        pop r8
-        mov flags, errno.SCREEN_FB_TOO_SMALL
-        jmp r13 ; return
-    size_ok:
-
-    ; Set screen mode
-	screen zr, r3
-    ; Set screen size
-    mov flags, SCREEN_SETTING_RESOLUTION
-    ; Setting is width/4 - 1
-    sub r4, r4, 1
-    screen flags, r4
-    ; Restore width
-    add r4, r4, 1
-    lsl r4, r4, 2
-
-    ; Set FB pointer
-    ; If double buffering..
-    cmp r6, 0
-    je save_fb_single_buff
-        ; ..we want the size of each FB
-        lsr r11, r11, 1
-        store_32 [globals.FB_SIZE_BYTE], r11
-        store_32 [globals.FB_DISPLAY_PTR], r2
-        mov r3, SCREEN_SETTING_DATA_OFFSET
-        screen r3, r2
-        add r2, r2, r11
-        jmp save_fb_done
-    save_fb_single_buff:
-        store_32 [globals.FB_SIZE_BYTE], r11
-        store_32 [globals.FB_DISPLAY_PTR], r2
-        mov r3, SCREEN_SETTING_DATA_OFFSET
-        screen r3, r2
-    save_fb_done:
-    store_32 [globals.FB_DRAW_PTR], r2
-    
-    store_16 [globals.FB_WIDTH_PX], r4
-    store_16 [globals.FB_HEIGHT_PX], r10
-    store_8 [globals.FB_LOG_WIDTH], r9
-    store_8 [globals.FB_LOG_BPP], r8
-    mov flags, 1
-    lsl r8, flags, r8
-    store_8 [globals.FB_BYTES_PER_PIXEL], r8
-
-    mov r1, r2 ; Return draw FB
-	mov r3, 0
-	mov r4, 0
-    ; TODO call clear
-	nor r2, zr, 0xff ; Colour = White (32-bit)
-
-    pop r11
-    pop r10
-    pop r9
-    pop r8
-    mov flags, 0 ; OK
-	jmp r13 ; return
-
-pub set_text_mode:
-; u16 set_text_mode(void *FB_ptr, size_t FB_size, u8 bit_per_pixel, u8 font, bool clear, bool double_buf)
-; Sets the screen to text mode, the font, and colour depth. Also sets fore ground and background colors.
-; Optionally clears the screen.
-
-; Arguments:
-; - r1: Address of allocated framebuffer
-; - r2: Size of FB allocation, in bytes
-; - r3: Bits per pixel: One of `8` or `32`
-; - r4: Font, one of {0,1,2,3}
-; - r5: If non-zero, clears the current framebuffer.
-; - r6: If non-zero, enable double buffering
-; Returns:
-; - r1: Status
-;   * 0 OK
-;   * SCREEN_INVALID_SIZE width invalid
-;   * SCREEN_INVALID_MODE bits_per_pixel invalid
-;   * SCREEN_FB_TOO_SMALL allocation too small
-; Clobbers:
-; - r2-r6, flags
-; Globals written:
-; - LOG_STRIDE
-; - FB_WIDTH
-; - FB_HEIGHT
-; - BITS_PER_PIXEL
-
-    ; Check the magic number
-    load_16 flags, [globals.MAGIC_ADDRESS]
-    cmp flags, globals.MAGIC_VALUE
-    je set_text_mode_magic_ok
-        mov flags, errno.MAGIC_BAD
-        jmp r13 ; return
-    set_text_mode_magic_ok:
-
-;TODO: Sanity checks
-;TODO: ?Clear screen
-    push r8 ; LOG Bytes/pixel
-    push r9 ; Log width
-    push r10 ; Height
-    push r11 ; Size of FB in bytes/pixels
-    
-    cmp r3, 32
-    jne not_32_bit_text_mode
-    mov r3, SCREEN_MODE_TEXT_32
-    mov r8, 2
-    jmp text_mode_ok
-    
-    not_32_bit_text_mode:
-    cmp r3, 8
-    jne invalid_text_mode
-    mov r3, SCREEN_MODE_TEXT_8
-    mov r8, 0
-    jmp text_mode_ok
-    
-    invalid_text_mode: 
-        pop r11
-        pop r10
-        pop r9
-        pop r8
-        mov flags, errno.SCREEN_INVALID_MODE
-        jmp r13 ; return
-    text_mode_ok:
-
-    ; Set screen mode
-	screen zr, r3
-
-    ; Set FB pointer
-    ; If double buffering..
-    cmp r6, 0
-    je save_fb_single_text_buff
-        ; ..we want the size of each FB
-        lsr r11, r11, 1
-        store_32 [globals.FB_SIZE_BYTE], r11
-        store_32 [globals.FB_DISPLAY_PTR], r2
-        mov r3, SCREEN_SETTING_DATA_OFFSET
-        screen r3, r2
-        add r2, r2, r11
-        jmp save_fb_text_done
-    save_fb_single_text_buff:
-        store_32 [globals.FB_SIZE_BYTE], r11
-        store_32 [globals.FB_DISPLAY_PTR], r2
-        mov r3, SCREEN_SETTING_DATA_OFFSET
-        screen r3, r2
-    save_fb_text_done:
-    store_32 [globals.FB_DRAW_PTR], r2
-
-    ; Set screen font
-    ; Only 0, 1, 2, 3 are valid
-    and r4, r4, 3
-    mov flags, SCREEN_SETTING_FONT
-    screen flags, r4
-
-	; Set foreground to white
-    mov flags, SCREEN_SETTING_FOREGROUND_COLOR
-	nor r4, zr, 0xff ; White    
-    screen flags, r4
-
-	; Set background to black	
-    mov flags, SCREEN_SETTING_BACKGROUND_COLOR
-	screen flags, zr
-	
-    pop r11
-    pop r10
-    pop r9
-    pop r8
-    mov flags, 0 ; OK
-	jmp r13 ; return
-
-pub set_text_mode_default:
-; u16 set_text_mode_default(void *FB_ptr)
-; Sets the screen to default text mode, the font, and colour depth. Also sets fore ground and background colors.
-; Does not clear the screen.
-; Size of allcation is not checked
-;
-; Arguments:
-; - r1: Address of allocated framebuffer
-; Returns:
-; - flags: 0 ; ok, never fails
-; Clobbers:
-; - r1, flags
-; Globals written:
-; - FB_DISPLAY_PTR
-; - FB_DRAW_PTR
-; - FRAME_BUFFER_SIZE
-
-    ; Set screen mode to default 8 bit text
-	screen zr, zr
-
-    ; Set FB pointer
-    store_32 [globals.FB_DISPLAY_PTR], r1
-    store_32 [globals.FB_DRAW_PTR], r1
-    ; Size is 96*40*1 byte
-    mov r1, 3840
-    store_32 [globals.FB_SIZE_BYTE], r1
-    mov flags, SCREEN_SETTING_DATA_OFFSET
-    screen flags, r1
-
-    ; Set default screen font
-    mov flags, SCREEN_SETTING_FONT
-    screen flags, zr
-
-	; Set foreground to white
-    mov flags, SCREEN_SETTING_FOREGROUND_COLOR
-	nor r1, zr, 0xff ; White
-    screen flags, r1
-
-	; Set background to black	
-    mov flags, SCREEN_SETTING_BACKGROUND_COLOR
-	screen flags, zr
-
-    mov flags, 0 ; OK
-    jmp r13
-
-pub clear:
-; void clear()
-; Paints the whole screen black
-;
-; Arguments:
-; - None
-; Clobbers:
-; - r1: Color
-; - r2: fill_screen
-; - r3: fill_screen
-; - r4: fill_screen
-; - flags
-
-	mov r1, 0 ; Black
-	; Fall through
-
-pub fill_screen:
-; void fill_screen(u32 color)
-; Fills the whole screen in a single color.
-;
-; Arguments:
-; - r1: Color, 32 bit RGB0
-; Clobbers:
-; - r2: Pixel pointer
-; - r3: End address
-; - r4: Stride
-; - flags
-; Reads globals:
-; - FB_DRAW_PTR
-; - LOG_BPP
-; - LOG_WIDTH
-; - PIXEL_HEIGHT
-
-	load_8 r2, [globals.FB_LOG_WIDTH]
-	load_16 r3, [globals.FB_HEIGHT_PX]
-	lsl r3, r3, r2
-	load_8 r4, [globals.FB_LOG_BPP]
-	lsl r3, r3, r4 ; Num bytes in FB
-	load_32 r2, [globals.FB_DRAW_PTR]
-	add r3, r3, r2 ; End of FB
-	load_8 r4, [globals.FB_BYTES_PER_PIXEL]
-	fill_screen_loop:
-		; Screen is always a multiple of 4*3
-		; we can unroll this 12 times.
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		store_32 [r2], r1
-		add r2, r2, r4
-		cmp r2, r3
-		jb fill_screen_loop
-
-	jmp r13 ; return
-
-
-pub switch_buffers: ; SHOULD BE INLINED
-; void switch_buffers()
-; Swaps the display and draw buffers, and updates the screen to use the new display buffer.
-;; Safe to run when single buffered.
-;
-; Arguments:
-; - None
-; Returns:
-; - None
-; Clobbers:
-; - r1: Old display FB => new draw FB
-; - r2: Old draw FB => new display FB
-; - flags
-; Globals written:
-; - FB_DISPLAY_PTR
-; - FB_DRAW_PTR
-
-    load_32 r1, [globals.FB_DISPLAY_PTR]
-    load_32 r2, [globals.FB_DRAW_PTR]
-    mov flags, SCREEN_SETTING_DATA_OFFSET
-    screen flags, r2
-    store_32 [globals.FB_DISPLAY_PTR], r2
-    store_32 [globals.FB_DRAW_PTR], r1
-    
-    jmp r13 ; return
-
-
-pub draw_pixel:
-; void draw_pixel(u32 color, u16 x, u16 y)
-; Draw pixel at the position, no checks on position, can potentally write to any memory.
-; Framebuffer pointer is stored in FB_PTR.
-;
-; Arguments:
-; - r1 Color 24 bit RGB0   PRESERVED
-; - r2 X coord             PRESERVED
-; - r3 Y coord             PRESERVED
-; - r4-r7 ignored but      PRESERVED
-; Result:
-; - None
-; Clobbers:
-; - flags
-; Globals read:
-; - FB_DRAW_PTR
-; - LOG_WIDTH
-
-    ; Screen is `1 << WIDTH pixels wide
-    load_8 flags, [globals.FB_LOG_WIDTH]
-	; Compute pixel address
-	lsl flags, r4, flags ; Y * width
-	add flags, flags, r3 ; Y * width + X
-	lsl flags, flags, 2 ; pixel to address
-    load_32 r1, [globals.FB_DRAW_PTR]
-	add flags, flags, r1 ; += frambuffer_ptr
-	; Set pixel value
-	store_32 [flags], r2
-	jmp r13 ; return
-
-
-pub draw_line_h:
-; void draw_line_h(u32 color, u16 x0, u16 y, u16 x1)
-; Draws a straight horizontal line from (x0, y) to (x1, y) (inclusive) using `color`
-; on to the current `FB_DRAW_PTR` buffer.
-;
-; Arguments:
-; - r1: Color 24 bit RGB0   PRESERVED
-; - r2: X0 coord
-; - r3: Y coord             PRESERVED
-; - r4: X1 coord
-; Returns:
-; - r1: Color 24 bit RGB0   PRESERVED
-; - r2: X1 coord
-; - r3: Y coord             PRESERVED
-; Clobbers:
-; - r7, flags
-
-	push r13
-
-	; if x0 > x1
-		; dx = -1
-	; else
-		; dx = +1
-	; endif
-	cmp r4, r2
-	or r7, flags, 0x02
-	lsl r7, r7, 29
-	asr r7, r7, 30
-
-	jmp draw_line_h_loop_in
-	draw_line_h_loop:
-		add r2, r2, r7
-	draw_line_h_loop_in:
-		qcall draw_pixel
-		cmp r2, r4
-		jne draw_line_h_loop
-
-	pop r13
-	jmp r13 ; return
-
-
-pub draw_line_v:
-; void draw_line_v(u32 color, u16 x, u16 _, u16 y0, u16 x1)
-; Draws a straight verticle line from (x, y0) to (x, y1) (inclusive) using `color`
-; on to the current `FB_DRAW_PTR` buffer.
-;
-; Arguments:
-; - r1: Color 24 bit RGB0   PRESERVED
-; - r2: X coord             PRESERVED
-; - r3: Y0 coord
-; - r4: ignored but         PRESERVED
-; - r5: Y1 coord
-
-; Returns:
-; - r1: Color 24 bit RGB0   PRESERVED
-; - r2: X coord             PRESERVED
-; - r3: Y1 coord
-; Clobbers:
-; - r7, flags
-
-	push r13
-
-	; if y0 > y1
-		; dy = -1
-	; else
-		; dy = +1
-	; endif
-	cmp r5, r3
-	or r7, flags, 0x02
-	lsl r7, r7, 29
-	asr r7, r7, 30
-
-	jmp draw_line_v_loop_in
-	draw_line_v_loop:
-		add r3, r3, r7
-	draw_line_v_loop_in:
-		qcall draw_pixel
-		cmp r3, r5
-		jne draw_line_v_loop
-
-	pop r13
-	jmp r13 ; return
-
-
-pub draw_line:
-; void draw_line(u32 color, u16 x0, u16 y0, u16 x1, u16 y1)
-; Draws a straight line from (x0, y0) to (x1, y1) (inclusive) using `color`
-; on to the current `FB_DRAW_PTR` buffer.
-;
-; Arguments:
-; - r1: Color 24 bit RGB0   PRESERVED
-; - r2: X0 coord
-; - r3: Y0 coord
-; - r4: X1 coord
-; - r5: Y1 coord
-; Returns:
-; - r1: Color 24 bit RGB0   PRESERVED
-; - r2: X1 coord
-; - r3: Y1 coord
-; Clobbers:
-; - r4-r7, flags
-; Globals read:
-; - FB_DRAW_PTR
-; - FB_DRAW_STRIDE
-; - ...others I expect
-
-;	push r11 ; sy
-;	push r10 ; dy
-;	push r9 ; sx
-;	push r8 ; dx
-
-    ; int dx = abs(x1-x0), sx = x0<x1 ? 1 : -1;
-    cmp r2, r4
-    ja draw_line_move_left
-    jb draw_line_move_right
-    ; if x0 == x1
-        jmp draw_line_v ; tail call
-    ; elif x0 < x1
-    draw_line_move_right:
-        push r8 ; dx
-        push r9 ; sx
-        sub r8, r4, r2
-        mov r9, 1
-        jmp draw_line_move_right_done
-    ; else x0 > x1
-    draw_line_move_left:
-        push r8 ; dx
-        push r9 ; sx
-        sub r8, r2, r4
-        nor r9, zr, zr ; sx = -1
-    ; endif
-    draw_line_move_right_done:
-
-    ; int dy = -abs(y1-y0), sy = y0<y1 ? 1 : -1;
-    cmp r3, r5
-    jb draw_line_move_down
-    ja draw_line_move_up
-    ; if y0 == y0
-        ; Restore r8, r9
-        pop r9
-        pop r8
-        jmp draw_line_h ; tail call
-    ; elif y0 < y1
-    draw_line_move_down:
-        push r10 ; dy
-        push r11 ; sy
-        sub r10, r3, r5
-        mov r11, 1
-        jmp draw_line_move_down_done
-    ; else y0 > y1
-    draw_line_move_up:
-        push r10 ; dy
-        push r11 ; sy
-        sub r10, r5, r3
-        nor r11, zr, zr ; sy = -1
-    ; endif
-    draw_line_move_down_done:
-
-	push r12 ; err, err2
-	push r13 ; lr
-
-    ; int err = dx+dy /* error value e_xy */
-    add r12, r8, r10
-    ; loop while(true)
-    draw_line_loop:
-     
-        qcall draw_pixel
-        ; err2 = 2*err;
-        lsl r12, r12, 1
-        ; if (err2 >= dy) { /* e_xy+e_x > 0 */
-        cmp r12, r10
-        lsr r12, r12, 1 ; restore err
-        jl draw_line_loop_skip_x
-            ; if (x0 == x1) break;
-            cmp r2, r4
-            je draw_line_loop_done
-            ; err += dy
-            add r12, r12, r10
-            ; x0 += sx;
-            add r2, r2, r9
-        draw_line_loop_skip_x:
-
-        ; err2 = 2*err;
-        lsl r12, r12, 1
-        ; if (err2 <= dx) { /* e_xy+e_y < 0 */
-        cmp r12, r8
-        lsl r12, r12, 1 ; restore err
-        jl draw_line_loop_skip_y
-            ; if (y0 == y1) break;
-            cmp r3, r5
-            je draw_line_loop_done
-            ; err += dx
-            add r12, r12, r8
-            ; y0 += sy
-            add r3, r3, r11
-        draw_line_loop_skip_y:
-	    jmp draw_line_loop
-    ; endloop
-    draw_line_loop_done:
-
-	pop r13
-	pop r12
-	pop r11
-	pop r10
-	pop r9
-	pop r8
-	jmp r13 ; return
-- 
2.54.0


From 736804433546585bcc64b81a00910baede179974 Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Sun, 6 Sep 2026 15:49:23 +0100
Subject: [PATCH 5/7] Global addresses now in hex and listed in order

---
 src/globals.asm | 50 ++++++++++++++++++++++++-------------------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/src/globals.asm b/src/globals.asm
index fa38ae2..3c86fb7 100755
--- a/src/globals.asm
+++ b/src/globals.asm
@@ -1,28 +1,28 @@
 ; Addresses of global variables
 
-; If not double buffering these point to the same buffer
-; If double buffering they must the same size
-pub const FB_DISPLAY_PTR     = 16 ; U32 Currently displayed buffer
-pub const FB_DISPLAY_STRIDE  = 20 ; U32 Bytes in each row of the displayed buffer
-pub const FB_DRAW_PTR        = 24 ; U32 Draw to this buffer
-pub const FB_DRAW_STRIDE     = 28 ; U32 Bytes in each row of the draw buffer
-pub const FB_SIZE_BYTE       = 32 ; U32 In bytes
-pub const FB_WIDTH_PX        = 36 ; U16 Width of screen in pixels
-pub const FB_HEIGHT_PX       = 38 ; U16 Height of screen in pixels
-
-; Log2 of width in pixels, e.g.
-; * 10 => 1024 * 768
-; *  8 =>  256 * 192
-pub const FB_LOG_WIDTH       = 40 ; U8
-pub const FB_LOG_STRIDE      = 41 ; U8 Log2 of FB_xxx_STRIDE in bytes
-
-pub const FB_BYTES_PER_PIXEL = 42 ; U8 Specialisations should hardcode this
-; Log2 of bytes per pixel
-; * 0 => 8 bits per pixel
-; * 2 => 32 bits per pixel
-pub const FB_LOG_BPP         = 43 ; U8 Specialisations should hardcode this
-
-pub const MAGIC_ADDRESS_LONG = 12 ; U32 Location of the magic value
+pub const MAGIC_ADDRESS_LONG = 0x0c       ; U32 Location of the magic value
 pub const MAGIC_VALUE_LONG   = 0xb301534c ; U32 Full 32 bits of the magic value
-pub const MAGIC_ADDRESS      = 14 ; U16 Location of the low 16 bits of magic value
-pub const MAGIC_VALUE        = 0x534c ; U16 Low 16 bits of the magic value
+pub const MAGIC_ADDRESS      = 0x0e       ; U16 Location of the low 16 bits of magic value
+pub const MAGIC_VALUE        = 0x534c     ; U16 Low 16 bits of the magic value
+      
+       ; If not double buffering these point to the same buffer
+       ; If double buffering they must the same size
+pub const FB_DISPLAY_PTR     = 0x10       ; U32 Currently displayed buffer
+pub const FB_DISPLAY_STRIDE  = 0x14       ; U32 Bytes in each row of the displayed buffer
+pub const FB_DRAW_PTR        = 0x18       ; U32 Draw to this buffer
+pub const FB_DRAW_STRIDE     = 0x1c       ; U32 Bytes in each row of the draw buffer
+pub const FB_SIZE_BYTE       = 0x20       ; U32 In bytes
+pub const FB_WIDTH_PX        = 0x24       ; U16 Width of screen in pixels
+pub const FB_HEIGHT_PX       = 0x26       ; U16 Height of screen in pixels
+      
+       ; Log2 of width in pixels, e.g.
+       ; * 10 => 1024 * 768
+       ; *  8 =>  256 * 192
+pub const FB_LOG_WIDTH       = 0x28       ; U8
+pub const FB_LOG_STRIDE      = 0x29       ; U8 Log2 of FB_xxx_STRIDE in bytes
+      
+pub const FB_BYTES_PER_PIXEL = 0x2a       ; U8 Specialisations should hardcode this
+       ; Log2 of bytes per pixel
+       ; * 0 => 8 bits per pixel
+       ; * 2 => 32 bits per pixel
+pub const FB_LOG_BPP         = 0x2b       ; U8 Specialisations should hardcode this
-- 
2.54.0


From ca5cff0a792fd087815f796c08f120fa5d87c0d7 Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Sun, 6 Sep 2026 16:25:40 +0100
Subject: [PATCH 6/7] Function premble should list error codes, if any

---
 CONTRIBUTING.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index f316bb3..b50237b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -17,6 +17,7 @@ All functions in the standard library should follow the following outline:
 ; Result: <what is the result, and where is it stored>
 ; Clobbers: <list of registers that are clobbered>
 ; Globals: <list of globals are accessed. OPTIONAL>
+; Errors: <list of any status codes returned in flags. OPTIONAL>
 <label>: <;SHOULD BE INLINED>
     <CODE>
 
-- 
2.54.0


From 48015204245ba8bb62e381624bc7f42f8fe31ba9 Mon Sep 17 00:00:00 2001
From: Gelthor <gelthor-gitea_sm@havnor.org.uk>
Date: Sun, 6 Sep 2026 17:37:49 +0100
Subject: [PATCH 7/7] Split framebuffer stride into stride and depth

Stride is now U16, depth is U16, and stores the bits per pixel of the
buffer.
---
 src/globals.asm | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/src/globals.asm b/src/globals.asm
index 3c86fb7..d9398c5 100755
--- a/src/globals.asm
+++ b/src/globals.asm
@@ -4,25 +4,27 @@ pub const MAGIC_ADDRESS_LONG = 0x0c       ; U32 Location of the magic value
 pub const MAGIC_VALUE_LONG   = 0xb301534c ; U32 Full 32 bits of the magic value
 pub const MAGIC_ADDRESS      = 0x0e       ; U16 Location of the low 16 bits of magic value
 pub const MAGIC_VALUE        = 0x534c     ; U16 Low 16 bits of the magic value
-      
-       ; If not double buffering these point to the same buffer
-       ; If double buffering they must the same size
+
+; If not double buffering these point to the same buffer
+; If double buffering they must the same size
 pub const FB_DISPLAY_PTR     = 0x10       ; U32 Currently displayed buffer
-pub const FB_DISPLAY_STRIDE  = 0x14       ; U32 Bytes in each row of the displayed buffer
+pub const FB_DISPLAY_STRIDE  = 0x14       ; U16 Bytes in each row of the displayed buffer
+pub const FB_DISPLAY_DEPTH   = 0x16       ; U16 Bits per pixel of the display buffer
 pub const FB_DRAW_PTR        = 0x18       ; U32 Draw to this buffer
-pub const FB_DRAW_STRIDE     = 0x1c       ; U32 Bytes in each row of the draw buffer
+pub const FB_DRAW_STRIDE     = 0x1c       ; U16 Bytes in each row of the draw buffer == FB_DISPLAY_STRIDE
+pub const FB_DRAW_DEPTH      = 0x1e       ; U16 Bits per pixel of the draw buffer == FB_DISPLAY_DEPTH
 pub const FB_SIZE_BYTE       = 0x20       ; U32 In bytes
 pub const FB_WIDTH_PX        = 0x24       ; U16 Width of screen in pixels
 pub const FB_HEIGHT_PX       = 0x26       ; U16 Height of screen in pixels
-      
-       ; Log2 of width in pixels, e.g.
-       ; * 10 => 1024 * 768
-       ; *  8 =>  256 * 192
+
+; Log2 of width in pixels, e.g.
+; * 10 => 1024 * 768
+; *  8 =>  256 * 192
 pub const FB_LOG_WIDTH       = 0x28       ; U8
 pub const FB_LOG_STRIDE      = 0x29       ; U8 Log2 of FB_xxx_STRIDE in bytes
-      
+
 pub const FB_BYTES_PER_PIXEL = 0x2a       ; U8 Specialisations should hardcode this
-       ; Log2 of bytes per pixel
-       ; * 0 => 8 bits per pixel
-       ; * 2 => 32 bits per pixel
-pub const FB_LOG_BPP         = 0x2b       ; U8 Specialisations should hardcode this
+; Log2 of bytes per pixel
+; * 0 => 8 bits per pixel
+; * 2 => 32 bits per pixel
+pub const FB_LOG_BPP         = 0x2b       ; U8 Specialisations should hardcode this
\ No newline at end of file
-- 
2.54.0