From d5c06116d3d1257b46c476cf73b634cf089bcb82 Mon Sep 17 00:00:00 2001
From: user <user@clank>
Date: Thu, 16 Jul 2026 00:31:27 +0200
Subject: wip: sys_read + serial console shell (read-store bug under
 investigation)

- sys_read (SYS_READ): blocking console input via external-clock serial poll;
  yields while waiting. Verified working (direct-echo cat: 'hi' -> 'hi').
- shell (PROG_SH): prompt/read/parse/fork+exec+wait; worker+hello programs;
  StrEqual/SkipName helpers; command table.
- init now execs the shell.
- KNOWN BUG: storing the typed char to the line buffer at $A000 (cart RAM of an
  exec'd program) corrupts the following sys_read; sys_write reading $A000 also
  returns $3E. Kernel syscalls themselves are correct; isolating the cart-RAM /
  exec RAM-bank interaction next.
---
 src/syscall.asm | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

(limited to 'src/syscall.asm')

diff --git a/src/syscall.asm b/src/syscall.asm
index 4b8771c..bf75865 100644
--- a/src/syscall.asm
+++ b/src/syscall.asm
@@ -36,7 +36,7 @@ SyscallTrap::
 SyscallTable:
     dw sys_exit                 ; 0
     dw sys_fork                 ; 1  FORK
-    dw sys_nosys                ; 2  READ  (TODO)
+    dw sys_read                 ; 2  READ
     dw sys_write                ; 3  WRITE
     dw sys_nosys                ; 4  OPEN  (TODO)
     dw sys_nosys                ; 5  CLOSE (TODO)
@@ -70,6 +70,25 @@ sys_write:
     ld a, b                     ; return len
     ret
 
+; -----------------------------------------------------------------------------
+; sys_read() -> A = one input byte from the console (blocking).
+; Uses an external-clock serial transfer as a clean RX: it completes only when
+; the host has a byte (no stdout echo). While waiting we yield so other procs
+; run. Preserves BC/DE/HL (the context switch saves/restores them).
+; -----------------------------------------------------------------------------
+sys_read:
+.poll
+    ld a, $80
+    ld [rSC], a                 ; request a byte (external clock)
+    ld a, [rSC]
+    bit 7, a
+    jr z, .got                  ; bit7 clear => transfer completed
+    call SchedYield             ; nothing yet: let others run, then retry
+    jr .poll
+.got
+    ld a, [rSB]
+    ret
+
 ; -----------------------------------------------------------------------------
 ; sys_getpid() -> A = current pid
 ; -----------------------------------------------------------------------------
-- 
cgit v1.3.1-sl0p