From ef88f0e530b898ebcb14f9e3dff1d58e83089ada Mon Sep 17 00:00:00 2001
From: user <user@clank>
Date: Thu, 16 Jul 2026 00:49:58 +0200
Subject: C toolchain: run SDCC-compiled C programs as gbos processes

- c/{gbos.h,crt0.s,libc.s,build.sh}: SDCC sm83 -> ROM-bank blob toolchain.
  libc syscall wrappers save/restore BC/DE/HL around rst $30 (trap clobbers
  them; SDCC expects them preserved).
- build via SDCC native asxxxx path (sdasgb/sdldgb), crt0 linked first so
  _start is the $4000 entry; blob INCBIN'd into a ROM bank.
- chello.c: prints a message + getpid() -> runs as 'chello' shell command.
- Makefile: auto-build c/*.bin, track as a dep of programs.o; gitignore blobs.
- README: document the C toolchain + the SDCC --asm=rgbds codegen bug that
  forced the native-toolchain approach.
- verified: '$ chello' -> 'hello from C on gbos!' / 'my pid is 2'.
---
 c/gbos.h | 9 +++++++++
 1 file changed, 9 insertions(+)
 create mode 100644 c/gbos.h

(limited to 'c/gbos.h')

diff --git a/c/gbos.h b/c/gbos.h
new file mode 100644
index 0000000..9a09a5d
--- /dev/null
+++ b/c/gbos.h
@@ -0,0 +1,9 @@
+/* gbos userland C API (thin wrappers over rst $30 syscalls; see c/libc.asm) */
+#ifndef GBOS_H
+#define GBOS_H
+void          writes(const char *buf, unsigned char len); /* write to console */
+void          nl(void);                                   /* newline (CRLF)   */
+unsigned char readc(void);                                /* read one byte    */
+void          sexit(unsigned char code);                  /* exit(code)       */
+unsigned char getpid(void);
+#endif
-- 
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