Initial disassembly

This commit is contained in:
Joshua Bell 2017-11-24 15:47:28 -08:00
commit a445735244
2 changed files with 152 additions and 0 deletions

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Makefile Normal file
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CC65 = ~/dev/cc65/bin
CAFLAGS = --target apple2enh --list-bytes 0
CCFLAGS = --config apple2-asm.cfg
TARGETS = cricket.SYS
.PHONY: clean all
all: $(TARGETS)
HEADERS = $(wildcard *.inc)
clean:
rm -f *.o
rm -f $(TARGETS)
%.o: %.s $(HEADERS)
$(CC65)/ca65 $(CAFLAGS) --listing $(basename $@).list -o $@ $<
%.SYS: %.o
$(CC65)/ld65 $(CCFLAGS) -o $@ $<

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cricket.s Normal file
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;;; The Cricket Clock Driver
;;; Adapted from /CRICKET/PRODOS.MOD
;;; Original: Street Electronics Corporation (C) 1984
.setcpu "6502"
.include "apple2.inc"
;; TODO:
;; * Move ORG to $2000
;; * Exit installer with MLI QUIT call
.org $300
;; ProDOS System Global Page
DATETIME := $BF06 ; CLOCK CALENDAR ROUTINE.
DATELO := $BF90 ; BITS 15-9=YR, 8-5=MO, 4-0=DAY
TIMELO := $BF92 ; BITS 12-8=HR, 5-0=MIN; LOW-HI FORMAT.
;; SSC I/O Registers (for Slot 2)
TDREG := $C088 + $20 ; ACIA Transmit Register (write)
RDREG := $C088 + $20 ; ACIA Receive Register (read)
STATUS := $C089 + $20 ; ACIA Status/Reset Register
COMMAND := $C08A + $20 ; ACIA Command Register (read/write)
CONTROL := $C08B + $20 ; ACIA Control Register (read/write)
.proc install
ptr := $42
lda DATETIME+1
sta ptr
lda DATETIME+2
sta ptr+1
lda #$4C ; JMP opcode
sta DATETIME
lda ROMIN
lda ROMIN
ldy #sizeof_driver-1
loop: lda driver,y
sta (ptr),y
dey
bpl loop
rts ; TODO: Replace with MLI QUIT call
.endproc
.proc driver
scratch := $3A ; ZP scratch location
;; Initialize
php
sei
lda COMMAND ; save status of command register
pha
;; Configure SSC
lda #%00001011
sta COMMAND
lda #%10011110 ; 9600 baud, 8 data bits, 1 stop bit
sta CONTROL
: lda STATUS
and #(1 << 4) ; transmit register empty? (bit 4)
beq :- ; nope, keep waiting
;; Send command
lda #('@' | $80)
sta TDREG
read_len := 7 ; read 7 bytes (?/M/D/Y/h/m/?)
;; Read response, pushing to stack
ldy #(read_len-1)
rloop: ldx #0 ; x = retry loop counter low byte
lda #3 ; scratch = retry loop counter high byte
sta scratch ; ($300 iterations total)
check: lda STATUS ; did we get it?
and #(1 << 3) ; receive register full? (bit 3)
bne ready ; yes, we read the value
inx ; not yet, so keep trying
bne check ; until counter runs out
dec scratch
bne check
;; Read failed - restore stack and exit
reset: cpy #(read_len-1) ; anything left to restore?
beq done ; nope, exit
pla ; yep, clear it off the stack
iny
bne reset
;; Read succeeded - stuff it on the stack and continue
ready: lda RDREG
pha
dey
bpl rloop
;; Convert pushed response to ProDOS time field
pla ; ???
pla ; minute
sta TIMELO ; -- stored as-is (TIMELO 5-0)
pla ; hour
sta TIMELO+1 ; -- stored as-is (TIMELO 12-8)
pla ; year
sta DATELO+1 ; -- will be shifted up by 1 (DATELO 15-9)
pla ; day
and #%00011111 ; -- masked, stored as is (DATELO 4-0)
sta DATELO
pla ; month
asl a ; -- shifted up (DATELO 8-5)
asl a
asl a
asl a
asl a
ora DATELO ; -- merge low 5 bits
sta DATELO
rol DATELO+1
pla ; ???
;; Restore prior state
done: pla ; restore saved command state
sta COMMAND
plp
rts
.endproc
sizeof_driver := .sizeof(driver)