mirror of
https://github.com/dpeckett/arduino-appleii.git
synced 2024-08-31 17:29:01 +00:00
169 lines
4.9 KiB
Arduino
169 lines
4.9 KiB
Arduino
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// Share speaker pin for output
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#define CASSETTE_READ_PIN A5
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#define SPEAKER_PIN 5
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#ifndef cbi
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#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
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#endif
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#ifndef sbi
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#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
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#endif
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void cassette_header(unsigned short periods) {
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// Header Tone
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for(int i = 0; i < periods*128; ++i) {
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds(650);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds(650);
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}
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// Sync pulse, one half cycle at 2500hz and then 2000hz
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// 2500 hz
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds(200);
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// 2000 hz
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds(250);
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}
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void cassette_write_byte(unsigned char val) {
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// Shift it out, MSB first
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x80) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x80) ? 500 : 250);
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//bit 6
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x40) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x40) ? 500 : 250);
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//bit 5
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x20) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x20) ? 500 : 250);
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//bit 4
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x10) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x10) ? 500 : 250);
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//bit 3
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x08) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x08) ? 500 : 250);
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//bit 2
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x04) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x04) ? 500 : 250);
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//bit 1
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x02) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x02) ? 500 : 250);
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//bit 0
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digitalWrite(SPEAKER_PIN, HIGH);
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delayMicroseconds((val&0x01) ? 500 : 250);
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digitalWrite(SPEAKER_PIN, LOW);
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delayMicroseconds((val&0x01) ? 500 : 250);
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}
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void cassette_write_block(unsigned short A1, unsigned short A2) {
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unsigned char checksum = 0xFF, val = 0;
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for(unsigned short addr = A1; addr <= A2; ++addr) {
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val = read8(addr);
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cassette_write_byte(val);
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checksum ^= val;
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}
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cassette_write_byte(checksum);
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// High idle for a little while, make sure all bits cleared
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digitalWrite(SPEAKER_PIN, HIGH);
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delay(10);
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digitalWrite(SPEAKER_PIN, LOW);
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}
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// Used to track center voltage
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float cassette_center_voltage = 512;
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// implement zero crossing detector
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boolean cassette_read_state() {
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static boolean zerocross_state = false;
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// get value
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short adc = (analogRead(CASSETTE_READ_PIN) - (short)cassette_center_voltage);
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// bias drift correction
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cassette_center_voltage += adc*0.05f;
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// ~7mv hysteresis
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if(zerocross_state && adc < -7) zerocross_state = false;
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else if(!zerocross_state && adc > 7) zerocross_state = true;
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return zerocross_state;
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}
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// figure out the duration of zero crossing
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short cassette_read_transition() {
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unsigned long start_time;
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static boolean last = false;
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boolean cur = last;
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// loop until state transition
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for(start_time = micros();cur == last;) cur = cassette_read_state();
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// update transition tracking
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last = cur;
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//return duration of transition us
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return micros() - start_time;
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}
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// Based loosely on steve wozniaks original algorithm
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boolean cassette_read_block(unsigned short A1, unsigned short A2) {
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short bitperiod;
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unsigned char val, checksum = 0xFF, datachecksum = 0x00;
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// Calibrate the zero crossing detector
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for(short i = 0; i < 10000; ++i) cassette_read_state();
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// find tape in edge
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cassette_read_transition();
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cassette_read_transition();
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// Small delay to allow things to settle
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delay(500);
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//wait for sync bit, short zero
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while(cassette_read_transition() > 300);
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// skip second cycle of sync bit
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cassette_read_transition();
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// start reading data
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for(unsigned short addr = A1; addr <= A2; ++addr) {
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// zero our byte of memory
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val = 0;
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for(unsigned char i = 8; i != 0; --i) {
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bitperiod = (cassette_read_transition() + cassette_read_transition()) / 2;
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if(bitperiod > 300) val |= _BV(i-1);
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}
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// write byte to memory
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write8(addr, val);
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// update checksum
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checksum ^= val;
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}
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// Read checksum
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for(unsigned char i = 8; i != 0; --i) {
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bitperiod = (cassette_read_transition() + cassette_read_transition()) / 2;
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if(bitperiod > 300) datachecksum |= _BV(i-1);
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}
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//return whether the data passes error checking
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return (datachecksum == checksum);
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}
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void cassette_begin() {
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// ADC prescale, 77khz
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sbi(ADCSRA,ADPS2);
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cbi(ADCSRA,ADPS1);
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cbi(ADCSRA,ADPS0);
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// internal pullup on analog pin
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digitalWrite(CASSETTE_READ_PIN, HIGH);
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// use 1.1v internal analog reference
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analogReference(INTERNAL);
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}
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