kernel: sys_sleep - a cooperative delay off the DIV timer (+ ping pacing)

There was no time source at all (IRQ vectors just reti; scheduler is purely
cooperative). The DIV register (FF04) free-runs at 16384 Hz regardless of
interrupts, so sys_sleep accumulates DIV deltas across SchedYields (other procs
keep running) until the requested number of 1/64-second units elapse.

- SYS_SLEEP(34): B = 1/64s units; libc gsleep(units) / msleep(ms) wrappers.
- ping now msleep(800) between echoes, so it paces like real ping instead of
  blasting all four at once.

Verified real-time (capped emulator): replies land ~0.85s apart. In --uncapped
runs the delay is GB-time (fast wall-clock), as expected.

1 files changed, 8 insertions, 1 deletions

diff --git a/c/libc.s b/c/libc.s
index 724fc3b..b413f3b 100644
--- a/c/libc.s
+++ b/c/libc.s
@@ -1,7 +1,7 @@
 	.module libc
 	.globl _writes, _putc, _puts, _nl, _strlen, _readc, _sexit, _getpid, _getargs
 	.globl _open, _close, _fgetc, _fputc, _flist, _fremove, _pipe, _ssend, _srecv, _srecv_nb, _pollin
-	.globl _sys_net
+	.globl _sys_net, _gsleep
 	;; 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.
@@ -123,6 +123,13 @@ _sys_net:
 	rst	#0x30
 	ret
 
+	;; void gsleep(unsigned char units /*A*/) - delay units*(1/64)s
+_gsleep:
+	ld	b, a
+	ld	c, #34			; SYS_SLEEP
+	rst	#0x30
+	ret
+
 	;; unsigned char pollin(void) -> A  (typed OSK char, or 0)
 _pollin:
 	ld	c, #32			; SYS_POLLIN