mirror of
https://github.com/nippur72/apple1-videocard-lib.git
synced 2024-12-23 04:29:46 +00:00
127 lines
4.6 KiB
C
127 lines
4.6 KiB
C
#include <utils.h>
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#include <apple1.h>
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#pragma start_address(0x3000)
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byte *const HEX1L = 0x24; // End address of dump block
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byte *const HEX1H = 0x25; //
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byte *const HEX2L = 0x26; // Begin address of dump block
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byte *const HEX2H = 0x27; //
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byte *const LASTSTATE = 0x29; // Last input state
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byte *const NUMPULSES = 0x30; // Number of long pulses to sync at the header
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byte *const TAPEIN = 0xC081; // Tape input
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byte *const DSP = 0xD012; // display data port
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void load_from_tape(word start_address, word end_address)
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{
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*((word *)HEX1L) = end_address;
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*((word *)HEX2L) = start_address;
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asm {
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// synchronizes with the short header
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syncstart: lda #24 // 24 cycles (3 bytes of $ff)
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sta NUMPULSES // count 24 cycles pulses
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jsr fullcycle // skip the first full cycle (when looping)
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nextsync: ldy #58 // full cycle duration
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jsr fullcycle // read a full cycle
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bcc syncstart // if short cycle found (c=0), redo from start
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dec NUMPULSES // else long cycle found, decrease count
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bne nextsync // if not 24 cycles, get next cycle
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// else read bit start and 32 bytes of data normally
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// the following routine was copied directly from the ACI ROM
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notstart: ldy #31 // try to detect the much shorter start bit
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jsr cmplevel //
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bcs notstart // start bit not detected yet!
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jsr cmplevel // wait for 2nd phase of start bit
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ldy #58 // set threshold value in middle
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rdbyte: ldx #8 // receiver 8 bits
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rdbit: pha
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jsr fullcycle // detect a full cycle
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pla
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rol // roll new bit into result
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ldy #57 // set threshold value in middle
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dex // decrement bit counter
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bne rdbit // read next bit!
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sta ($26,x) // save new byte *** same as "STA (HEX2L,X)" see KickC bug #756 https://gitlab.com/camelot/kickc/-/issues/756
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jsr incaddr // increment address
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ldy #53 // compensate threshold with workload
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bcc rdbyte // do next byte if not done yet!
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bcs restidx // always taken! restore parse index
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fullcycle: jsr cmplevel // wait for two level changes
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cmplevel: dey // decrement time counter
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lda TAPEIN // get tape in data
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cmp LASTSTATE // same as before?
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beq cmplevel // yes!
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sta LASTSTATE // save new data
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cpy #128 // compare threshold
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rts
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// [...]
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incaddr: lda HEX2L // compare current address with
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cmp HEX1L // end address
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lda HEX2H
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sbc HEX1H
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inc HEX2L // and increment current address
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bne nocarry // no carry to msb!
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inc HEX2H
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nocarry: rts
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// end of read routine "restidx" is the exit point
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restidx: rts
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}
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}
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// converts the hexadecimal string argument to 16 bit word
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word xtow(byte *str) {
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word res=0;
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byte c;
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for(byte i=0; c=str[i]; ++i) {
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res = res << 4;
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if(c<'A') res += (c-'0');
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else res += (c-'A');
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}
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return res;
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}
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byte keybuf[32];
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void main() {
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woz_puts("\r\rTAPE ALTERNATE LOAD\r");
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word start_address;
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word end_address;
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woz_puts("\rSTART ADDRESS: "); apple1_input_line(keybuf, 32); start_address = xtow(keybuf);
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woz_puts("\rEND ADDRESS: "); apple1_input_line(keybuf, 32); end_address = xtow(keybuf);
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end_address += 1; // include checksum byte
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while(1) {
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woz_puts("\r\rPRESS PLAY ON TAPE\r\r");
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load_from_tape(start_address, end_address);
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// calculate checksum
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byte chk = 0xFF;
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for(byte *t=start_address; t<end_address; t++) {
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chk ^= *t;
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}
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if(chk == 0) {
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woz_puts("OK\r");
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break;
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}
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woz_puts("?LOAD ERROR\r\r");
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woz_puts("RETRY ? (Y/N) ");
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if(apple1_getkey()!='Y') break;
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}
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woz_mon();
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}
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