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Add globals and error codes

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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.
This commit is contained in:
Gelthor
2026-09-06 11:02:27 +01:00
parent 04f3f03ad5
commit 46abf8d893
6 changed files with 730 additions and 14 deletions
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README.md
+7 -2
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@@ -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