diff options
Diffstat (limited to 'src/keybuf.s')
| -rw-r--r-- | src/keybuf.s | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/src/keybuf.s b/src/keybuf.s new file mode 100644 index 0000000..cf24e77 --- /dev/null +++ b/src/keybuf.s @@ -0,0 +1,94 @@ + .fopt compiler,"cc65 v 2.12.9" + .setcpu "6502" + .smart on + .autoimport on + .case on + .debuginfo off + .importzp sp, sreg, regsave, regbank, tmp1, ptr1, ptr2 + .export _keybuf_init, _keybuf_poll_kbd, _keybuf_cgetc + +NO_KEY = $FF +max_buf_len = 12 ; aka buffer size + +BUFFER_BASE = $F0 + +keybuf_head = BUFFER_BASE +keybuf_tail = BUFFER_BASE+1 +keybuf = BUFFER_BASE+2 +keybuf_end = keybuf + max_buf_len + +CH = $02FC + + .segment "CODE" + +; void __fastcall__ keybuf_init(void) +_keybuf_init: + lda #keybuf + sta keybuf_head + sta keybuf_tail + rts + +; void __fastcall__ keybuf_poll_kbd(void) +_keybuf_poll_kbd: + lda CH + cmp #NO_KEY + beq kbpoll_done + + ; got a key, see if room in buffer + ldx keybuf_tail + cpx #keybuf_end+1 + bcs kbpoll_done + + ; buffer not full, so store key in buffer + sta 0,x + inc keybuf_tail + + ; clear keyboard register + lda #NO_KEY + sta CH + +kbpoll_done: + rts + + +; char __fastcall__ keybuf_is_empty(void) +_keybuf_is_empty: + ldx #0 + sec + lda keybuf_tail + sbc keybuf_head + rts + + +; char __fastcall__ keybuf_cgetc(void) + +; Note: 0 means "no key pressed", which means we +; can't return character code 0 (not a big deal). +; If this is a problem, we could change the return +; type to int, and return -1 instead. + +_keybuf_cgetc: + ldx keybuf_head + cpx keybuf_tail + beq check_ch + + ; got a key, stuff it in CH + lda 0,x + sta CH + inc keybuf_head + +call_cgetc: + ; ...and return the ASCII code + jmp _fuji_cgetc + +check_ch: + jsr _keybuf_init + + ldx CH + cpx #NO_KEY + bne call_cgetc + + inx ; was $FF, now 0 + txa ; aka return(0) + rts + |