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|
; =============================================================================
; programs.asm - userland program images (text-in-ROM model) + the shell.
;
; Programs are linked to run from the ROMX window ($4000-$7FFF) and live in
; their own ROM banks. exec() maps the bank and jumps in. Programs talk to the
; kernel only via `rst $30`.
; =============================================================================
INCLUDE "include/gbos.inc"
; the shell keeps its line buffer + scratch at the bottom of its RAM bank
DEF SH_LINEBUF EQU $A000 ; up to 32 bytes
DEF SH_PROGID EQU $A040 ; chosen program id (survives fork via bank copy)
DEF SH_MAXLINE EQU 32
; -----------------------------------------------------------------------------
; PROG_WORKER (bank 2) - print a line, exit(0).
; -----------------------------------------------------------------------------
SECTION "prog_worker", ROMX[$4000], BANK[2]
ProgWorker:
ld de, .msg
ld b, .msgend - .msg
ld c, SYS_WRITE
rst $30
ld b, 0
ld c, SYS_EXIT
rst $30
.msg
db "worker!", $0D, $0A
.msgend
; -----------------------------------------------------------------------------
; PROG_HELLO (bank 4) - print a line, exit(0).
; -----------------------------------------------------------------------------
SECTION "prog_hello", ROMX[$4000], BANK[4]
ProgHello:
ld de, .msg
ld b, .msgend - .msg
ld c, SYS_WRITE
rst $30
ld b, 0
ld c, SYS_EXIT
rst $30
.msg
db "hello world!", $0D, $0A
.msgend
; -----------------------------------------------------------------------------
; PROG_CHELLO (bank 5) - a program written in C, compiled with SDCC to a
; self-contained ROM-bank image (crt0 + libc + code) and included verbatim.
; Rebuild with: sh c/build.sh c/chello.c c/chello.bin
; -----------------------------------------------------------------------------
SECTION "prog_chello", ROMX[$4000], BANK[5]
ProgChello:
INCBIN "c/chello.bin"
; -----------------------------------------------------------------------------
; PROG_SH (bank 3) - a tiny shell.
; prompt -> read a line (with echo) -> match a command -> fork+exec+wait.
; -----------------------------------------------------------------------------
SECTION "prog_sh", ROMX[$4000], BANK[3]
ProgSh:
.prompt
ld de, .ps1
ld b, 2
ld c, SYS_WRITE
rst $30
; read a line into SH_LINEBUF, echoing as we go
ld hl, SH_LINEBUF
.rd
push hl ; syscalls clobber HL (trap uses it to dispatch)
ld c, SYS_READ
rst $30 ; A = input byte
pop hl
cp $0D
jr z, .eol
cp $0A
jr z, .eol
ld [hl], a ; store in the line buffer (A preserved)
inc hl
ld [$FF01], a ; echo the char straight to serial
ld a, $81
ld [$FF02], a
ld a, l
cp LOW(SH_LINEBUF) + SH_MAXLINE - 1
jr c, .rd ; keep reading unless the buffer is full
.eol
ld [hl], 0 ; NUL-terminate
ld de, .crlf
ld b, 2
ld c, SYS_WRITE
rst $30
ld a, [SH_LINEBUF]
or a
jr z, .prompt ; empty line
; look the command up in the table
ld de, .cmdtab
.scan
ld a, [de]
or a
jr z, .unknown ; empty name = end of table
push de
ld hl, SH_LINEBUF
call StrEqual ; Z set if equal
pop de
jr z, .match
call SkipName ; DE -> NUL after this name
inc de ; -> program id
inc de ; -> next entry
jr .scan
.match
call SkipName
inc de ; DE -> program id
ld a, [de]
ld [SH_PROGID], a
ld c, SYS_FORK
rst $30
or a
jr z, .exec
ld c, SYS_WAIT ; parent: reap the command
rst $30
jr .prompt
.exec
ld a, [SH_PROGID]
ld b, a
ld c, SYS_EXEC
rst $30 ; child becomes the command
.unknown
ld de, .huh
ld b, 3
ld c, SYS_WRITE
rst $30
jr .prompt
.ps1
db "$ "
.crlf
db $0D, $0A
.huh
db "?", $0D, $0A
.cmdtab
db "worker", 0
db PROG_WORKER
db "hello", 0
db PROG_HELLO
db "chello", 0
db PROG_CHELLO
db 0 ; terminator
; -----------------------------------------------------------------------------
; Shell string helpers (ROM0, always mapped).
; -----------------------------------------------------------------------------
SECTION "shell_lib", ROM0
; StrEqual(HL, DE) - compare NUL-terminated strings. Z set if equal.
; Clobbers A, B; advances HL and DE.
StrEqual::
.l
ld a, [de]
ld b, a
ld a, [hl]
cp b
ret nz
or a
ret z ; both NUL -> equal
inc hl
inc de
jr .l
; SkipName(DE) - advance DE to its NUL terminator.
SkipName::
.l
ld a, [de]
or a
ret z
inc de
jr .l
; -----------------------------------------------------------------------------
; Program table (ROM0). Index = program id. Entry: bank (2) + entry addr (2).
; -----------------------------------------------------------------------------
SECTION "progtab", ROM0
ProgramTable::
db LOW(BANK(ProgWorker)), HIGH(BANK(ProgWorker))
dw ProgWorker
db LOW(BANK(ProgSh)), HIGH(BANK(ProgSh))
dw ProgSh
db LOW(BANK(ProgHello)), HIGH(BANK(ProgHello))
dw ProgHello
db LOW(BANK(ProgChello)), HIGH(BANK(ProgChello))
dw ProgChello
|
