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.

1 files changed, 4 insertions, 58 deletions

diff --git a/src/tasks.asm b/src/tasks.asm
index 028d074..687bddf 100644
--- a/src/tasks.asm
+++ b/src/tasks.asm
@@ -1,67 +1,13 @@
 ; =============================================================================
-; tasks.asm - init exercises the full process lifecycle.
-;
-; init fork()s three children; each child exec()s PROG_WORKER, which prints 'w'
-; and exit()s with its pid as the status. init then wait()s in a loop, printing
-; 'R' + the reaped pid digit for each child, until wait() returns $FF (no more
-; children), then prints '!' and idles. This drives fork + exec + exit + wait +
-; zombie reaping + cart-RAM bank recycling.
-;
-; The fork counter lives at $A000 (bottom of init's own RAM bank) because the
-; register file does not survive a fork() call.
+; tasks.asm - init just becomes the shell.
+; init (pid 1) exec()s PROG_SH; the shell then drives fork+exec+wait to run
+; commands typed on the serial console. As pid 1 it is also the orphan reaper.
 ; =============================================================================
 INCLUDE "include/gbos.inc"
 
-DEF ASCII0 EQU $30          ; '0', added to a pid to print it as a digit
-DEF CH_R   EQU $52          ; 'R'
-DEF CH_BANG EQU $21         ; '!'
-
 SECTION "tasks", ROM0
 
 TaskInit::
-    ld a, 3
-    ld [$A000], a           ; children left to spawn
-
-.forkloop
-    ld c, SYS_FORK
-    rst $30
-    or a
-    jr z, .child            ; A==0 -> we are the child
-    ; parent: one more child spawned
-    ld a, [$A000]
-    dec a
-    ld [$A000], a
-    jr nz, .forkloop
-
-.waitloop
-    ld c, SYS_WAIT
-    rst $30                 ; A = reaped pid (B = code), or $FF if none left
-    cp $FF
-    jr z, .done
-    ; print 'R' then the reaped pid as a digit
-    push af
-    ld a, CH_R
-    ld [$FF01], a
-    ld a, $81
-    ld [$FF02], a
-    pop af
-    add ASCII0
-    ld [$FF01], a
-    ld a, $81
-    ld [$FF02], a
-    jr .waitloop
-
-.done
-    ld a, CH_BANG
-    ld [$FF01], a
-    ld a, $81
-    ld [$FF02], a
-.idle
-    ld c, SYS_YIELD
-    rst $30
-    jr .idle
-
-.child
-    ld b, PROG_WORKER
+    ld b, PROG_SH
     ld c, SYS_EXEC
     rst $30                 ; never returns