1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
|
; =============================================================================
; 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_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 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
|
