apple1-videocard-lib/demos/tapemon/tapeload.c

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2022-01-18 14:17:58 +00:00
#include <utils.h>
#include <apple1.h>
#pragma start_address(0x3000)
byte *const HEX1L = 0x24; // End address of dump block
byte *const HEX1H = 0x25; //
byte *const HEX2L = 0x26; // Begin address of dump block
byte *const HEX2H = 0x27; //
byte *const LASTSTATE = 0x29; // Last input state
byte *const NUMPULSES = 0x30; // Number of long pulses to sync at the header
byte *const TAPEIN = 0xC081; // Tape input
byte *const DSP = 0xD012; // display data port
void load_from_tape(word start_address, word end_address)
{
*((word *)HEX1L) = end_address;
*((word *)HEX2L) = start_address;
asm {
// synchronizes with the short header
syncstart: lda #24 // 24 cycles (3 bytes of $ff)
sta NUMPULSES // count 24 cycles pulses
jsr fullcycle // skip the first full cycle (when looping)
nextsync: ldy #58 // full cycle duration
jsr fullcycle // read a full cycle
bcc syncstart // if short cycle found (c=0), redo from start
dec NUMPULSES // else long cycle found, decrease count
bne nextsync // if not 24 cycles, get next cycle
// else read bit start and 32 bytes of data normally
// the following routine was copied directly from the ACI ROM
notstart: ldy #31 // try to detect the much shorter start bit
jsr cmplevel //
bcs notstart // start bit not detected yet!
jsr cmplevel // wait for 2nd phase of start bit
ldy #58 // set threshold value in middle
rdbyte: ldx #8 // receiver 8 bits
rdbit: pha
jsr fullcycle // detect a full cycle
pla
rol // roll new bit into result
ldy #57 // set threshold value in middle
dex // decrement bit counter
bne rdbit // read next bit!
sta ($26,x) // save new byte *** same as "STA (HEX2L,X)" see KickC bug #756 https://gitlab.com/camelot/kickc/-/issues/756
jsr incaddr // increment address
ldy #53 // compensate threshold with workload
bcc rdbyte // do next byte if not done yet!
bcs restidx // always taken! restore parse index
fullcycle: jsr cmplevel // wait for two level changes
cmplevel: dey // decrement time counter
lda TAPEIN // get tape in data
cmp LASTSTATE // same as before?
beq cmplevel // yes!
sta LASTSTATE // save new data
cpy #128 // compare threshold
rts
// [...]
incaddr: lda HEX2L // compare current address with
cmp HEX1L // end address
lda HEX2H
sbc HEX1H
inc HEX2L // and increment current address
bne nocarry // no carry to msb!
inc HEX2H
nocarry: rts
// end of read routine "restidx" is the exit point
restidx: rts
}
}
// converts the hexadecimal string argument to 16 bit word
word xtow(byte *str) {
word res=0;
byte c;
for(byte i=0; c=str[i]; ++i) {
res = res << 4;
if(c<'A') res += (c-'0');
else res += (c-'A');
}
return res;
}
byte keybuf[32];
void main() {
woz_puts("\r\rTAPE ALTERNATE LOAD\r");
word start_address;
word end_address;
woz_puts("\rSTART ADDRESS: "); apple1_input_line(keybuf, 32); start_address = xtow(keybuf);
woz_puts("\rEND ADDRESS: "); apple1_input_line(keybuf, 32); end_address = xtow(keybuf);
end_address += 1; // include checksum byte
while(1) {
woz_puts("\r\rPRESS PLAY ON TAPE\r\r");
load_from_tape(start_address, end_address);
// calculate checksum
byte chk = 0xFF;
for(byte *t=start_address; t<end_address; t++) {
chk ^= *t;
}
if(chk == 0) {
woz_puts("OK\r");
break;
}
woz_puts("?LOAD ERROR\r\r");
woz_puts("RETRY ? (Y/N) ");
if(apple1_getkey()!='Y') break;
}
woz_mon();
}