libc + CLI tools: a small C userland

- libc: add putc, puts, strlen, getargs (args string), EOF (=4) for readc.
- args: shell splits the command line at the first space ("cmd\0args\0" at
  $A000, inherited by the child via fork); getargs() returns the arg string.
- shell: exit on Ctrl-D/EOF; $ prompt over a clean read loop.
- tools (c/): echo (argv), cat (stdin->stdout to EOF), uname, pid (decimal
  print), true, false. Each built to a ROM-bank blob and registered.
- Makefile: CBLOBS list builds all C programs.
- README: document libc + the tool set.

1 files changed, 58 insertions, 26 deletions

diff --git a/c/libc.s b/c/libc.s
index 4fca5e3..29031e9 100644
--- a/c/libc.s
+++ b/c/libc.s
@@ -1,19 +1,48 @@
 	.module libc
-	.globl _writes, _nl, _readc, _sexit, _getpid
+	.globl _writes, _putc, _puts, _nl, _strlen, _readc, _sexit, _getpid, _getargs
+	;; SDCC sm83 sdcccall(1): 1st arg -> A (byte) or DE (pointer); ret A / BC.
+	;; rst $30 (the trap) clobbers BC/DE/HL; SDCC treats them caller-saved, so
+	;; wrappers need not preserve them - but we compute cleanly regardless.
 	.area _CODE
+
 	;; void writes(const char *buf /*DE*/, unsigned char len /*A*/)
 _writes:
-	push	hl
-	push	de
-	push	bc
 	ld	b, a
-	ld	c, #3		; SYS_WRITE
+	ld	c, #3			; SYS_WRITE
 	rst	#0x30
-	pop	bc
-	pop	de
-	pop	hl
 	ret
-	;; void nl(void) - CRLF straight to serial
+
+	;; char *getargs(void) -> BC : the arg string (command line past word 1).
+	;; The shell leaves "cmd\0args\0" at 0xA000, inherited by the child via fork.
+_getargs:
+	ld	hl, #0xa000
+1$:	ld	a, (hl)
+	inc	hl
+	or	a
+	jr	nz, 1$
+	ld	b, h
+	ld	c, l
+	ret
+
+	;; void putc(char c /*A*/)
+_putc:
+	ld	(0xff01), a
+	ld	a, #0x81
+	ld	(0xff02), a
+	ret
+
+	;; void puts(const char *s /*DE*/) - write until NUL (no newline)
+_puts:
+1$:	ld	a, (de)
+	or	a
+	ret	z
+	ld	(0xff01), a
+	ld	a, #0x81
+	ld	(0xff02), a
+	inc	de
+	jr	1$
+
+	;; void nl(void) - CRLF
 _nl:
 	ld	a, #0x0d
 	ld	(0xff01), a
@@ -24,31 +53,34 @@ _nl:
 	ld	a, #0x81
 	ld	(0xff02), a
 	ret
-	;; unsigned char readc(void) -> A
+
+	;; unsigned char strlen(const char *s /*DE*/) -> A
+_strlen:
+	ld	c, #0
+1$:	ld	a, (de)
+	or	a
+	jr	z, 2$
+	inc	c
+	inc	de
+	jr	1$
+2$:	ld	a, c
+	ret
+
+	;; char readc(void) -> A   (4 = EOF)
 _readc:
-	push	hl
-	push	de
-	push	bc
-	ld	c, #2		; SYS_READ
+	ld	c, #2			; SYS_READ
 	rst	#0x30
-	pop	bc
-	pop	de
-	pop	hl
 	ret
-	;; void sexit(unsigned char code /*A*/)
+
+	;; void sexit(unsigned char code /*A*/) - never returns
 _sexit:
 	ld	b, a
-	ld	c, #0		; SYS_EXIT
+	ld	c, #0			; SYS_EXIT
 	rst	#0x30
 	ret
+
 	;; unsigned char getpid(void) -> A
 _getpid:
-	push	hl
-	push	de
-	push	bc
-	ld	c, #8		; SYS_GETPID
+	ld	c, #8			; SYS_GETPID
 	rst	#0x30
-	pop	bc
-	pop	de
-	pop	hl
 	ret