collapseos/kernel/sms/pad.asm
Virgil Dupras 74de1c92cf sms/pad: implement character selection mechanism
Still a bit rough around the edges, but still, works rather well.
2019-07-02 13:12:52 -04:00

167 lines
3.6 KiB
NASM

; pad - read input from MD controller
;
; Conveniently expose an API to read the status of a MD pad A. Moreover,
; implement a mechanism to input arbitrary characters from it. It goes as
; follow:
;
; * Direction pad select characters. Up/Down move by one, Left/Right move by 5\
; * Start acts like Return
; * A acts like Backspace
; * B changes "character class": lowercase, uppercase, numbers, special chars.
; The space character is the first among special chars.
; * C confirms letter selection
;
; *** Consts ***
;
.equ PAD_CTLPORT 0x3f
.equ PAD_D1PORT 0xdc
.equ PAD_UP 0
.equ PAD_DOWN 1
.equ PAD_LEFT 2
.equ PAD_RIGHT 3
.equ PAD_BUTB 4
.equ PAD_BUTC 5
.equ PAD_BUTA 6
.equ PAD_START 7
; *** Variables ***
;
; Button status of last padUpdateSel call. Used for debouncing.
.equ PAD_SELSTAT PAD_RAMSTART
; Button status of last padGetC call.
.equ PAD_GETCSTAT PAD_SELSTAT+1
; Current selection "class". 0 = lowcase, 1 = upcase, 2 = num, 3 = symbols
.equ PAD_SELCLASS PAD_GETCSTAT+1
; Current selected character
.equ PAD_SELCHR PAD_SELCLASS+1
; Whether current sel is "new", that is, that its value has never been fetched
; though padUpdateSel. This flag is set when "avancing" in GetC and also on
; module init.
.equ PAD_SELNEW PAD_SELCHR+1
.equ PAD_RAMEND PAD_SELNEW+1
; *** Code ***
padInit:
ld a, 0xff
ld (PAD_SELSTAT), a
ld (PAD_GETCSTAT), a
ld (PAD_SELNEW), a
xor a
ld (PAD_SELCLASS), a
ld a, 'a'
ld (PAD_SELCHR), a
ret
; Put status for port A in register A. Bits, from MSB to LSB:
; Start - A - C - B - Right - Left - Down - Up
; Each bit is high when button is unpressed and low if button is pressed. For
; example, when no button is pressed, 0xff is returned.
padStatus:
; This logic below is for the Genesis controller, which is modal. TH is
; an output pin that swiches the meaning of TL and TR. When TH is high
; (unselected), TL = Button B and TR = Button C. When TH is low
; (selected), TL = Button A and TR = Start.
push bc
ld a, 0b11111101 ; TH output, unselected
out (PAD_CTLPORT), a
in a, (PAD_D1PORT)
and 0x3f ; low 6 bits are good
ld b, a ; let's store them
; Start and A are returned when TH is selected, in bits 5 and 4. Well
; get them, left-shift them and integrate them to B.
ld a, 0b11011101 ; TH output, selected
out (PAD_CTLPORT), a
in a, (PAD_D1PORT)
and 0b00110000
sla a
sla a
or b
pop bc
ret
; From a pad status in A, update current char selection and return it.
; Returns the same Z as padStatus: set if unchanged, unset if changed
padUpdateSel:
; special case: when selnew is set, always return current sel and
; disable selnew
ld a, (PAD_SELNEW)
or a
jr z, .notnew
; selection is new, return it
xor a
ld (PAD_SELNEW), a
ld a, (PAD_SELCHR)
jp unsetZ
.notnew:
call padStatus
push hl
ld hl, PAD_SELSTAT
cp (hl)
ld (hl), a
pop hl
jr z, .nothing ; nothing changed
bit PAD_UP, a
jr z, .up
bit PAD_DOWN, a
jr z, .down
bit PAD_LEFT, a
jr z, .left
bit PAD_RIGHT, a
jr z, .right
jr .nothing
.up:
ld a, (PAD_SELCHR)
inc a
jr .setchr
.down:
ld a, (PAD_SELCHR)
dec a
jr .setchr
.left:
ld a, (PAD_SELCHR)
dec a \ dec a \ dec a \ dec a \ dec a
jr .setchr
.right:
ld a, (PAD_SELCHR)
inc a \ inc a \ inc a \ inc a \ inc a
jr .setchr
.setchr:
ld (PAD_SELCHR), a
jp unsetZ
.nothing:
cp a ; ensure Z
ld a, (PAD_SELCHR)
ret
padGetC:
call padStatus
push hl
ld hl, PAD_GETCSTAT
cp (hl)
ld (hl), a
pop hl
jp z, unsetZ ; nothing changed
bit PAD_BUTC, a
jr z, .advance
bit PAD_BUTA, a
jr z, .backspace
bit PAD_START, a
jr z, .return
jp unsetZ
.advance:
ld a, 1
ld (PAD_SELNEW), a
ld a, (PAD_SELCHR)
cp a
ret
.backspace:
ld a, ASCII_BS
cp a
ret
.return:
ld a, ASCII_LF
cp a
ret