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Refactor playback ISR thanks to @matsstaff (#45)
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* TAP play ISR refactor

* comment updates
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@sweetlilmre
sweetlilmre authored Feb 10, 2022
1 parent 3d5378c commit af871e6
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Showing 2 changed files with 49 additions and 71 deletions.
118 changes: 48 additions & 70 deletions tapuino.c
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Original file line number Diff line number Diff line change
Expand Up @@ -180,10 +180,13 @@ ISR(TIMER1_OVF_vect){
}
}


// timer1 is running at 2MHz or 0.5 uS per tick.
// signal values are measured in uS, so OCR1A is set to the value from the TAP file (converted into uS) for each signal half
// for v0 and v1 TAP files that means that we will use the same signal value twice (1 for each half of the wave)
// i.e. TAP value converted to uS * 2 == full signal length
// for v2 TAP files we will read the 2nd half of the signal from the TAP file for the 2nd half of the wave
//
// Thanks to @matsstaff for his contributions on refactoring this code
ISR(TIMER1_COMPA_vect) {
uint32_t tap_data;

Expand All @@ -194,93 +197,66 @@ ISR(TIMER1_COMPA_vect) {
if (MOTOR_IS_OFF() || g_is_paused) {
return;
}

if (g_signal_2nd_half) { // 2nd half of the signal
if (g_pulse_length > 0xFFFF) { // check to see if its bigger than 16 bits
g_pulse_length -= 0xFFFF;
OCR1A = 0xFFFF;
} else {
OCR1A = (unsigned short) g_pulse_length;
g_pulse_length = 0; // clear this, for 1st half check so that the next data is loaded
g_signal_2nd_half = 0; // next time round switch to 1st half
}
if (g_invert_signal) {
TAPE_READ_LOW(); // set the signal high
} else {
TAPE_READ_HIGH(); // set the signal high
}
} else { // 1st half of the signal
if (g_pulse_length) { // do we have any pulse left?
if (g_pulse_length > 0xFFFF) { // check to see if its bigger than 16 bits
g_pulse_length -= 0xFFFF;
OCR1A = 0xFFFF;
} else {
OCR1A = (unsigned short) g_pulse_length;
g_pulse_length = g_pulse_length_save; // restore pulse length for the 2nd half of the signal
g_signal_2nd_half = 1; // next time round switch to 2nd half
}
} else {

if (g_pulse_length == 0) { // If this is the first time in, or the current pulse time has elapsed, then
if (g_pulse_length_save != 0) { // if g_pulse_length_save > 0 then we have a non v2 format, so restore the pulse value and count down again for the 2nd half
g_pulse_length = g_pulse_length_save;
g_pulse_length_save = 0; // making sure to clear g_pulse_length_save!
} else { // otherwise load a new pulse value from the TAP file
g_total_timer_count = 0;
if (g_tap_file_pos >= g_tap_info.length) {

if (g_tap_file_pos >= g_tap_info.length) { // basic sanity check to see if we have any TAP data left!
g_tap_file_complete = 1;
return; // reached the end of the TAP file so don't process any more!
return; // reached the end of the TAP file so don't process any more!
}
tap_data = (unsigned long) g_fat_buffer[g_read_index++];
g_tap_file_pos++;

// code for format 0 handling
tap_data = (uint32_t) g_fat_buffer[g_read_index++];

// code for v0 TAP handling, a zero in a v0 file indicates an overflow, we replace by 256
if (g_tap_info.version == 0 && tap_data == 0) {
tap_data = 256;
}

// if tap_data != 0 then this is a simple 8 bit pulse
if (tap_data != 0) {
g_pulse_length = tap_data * g_cycle_mult_8;
} else {
g_pulse_length = (unsigned long) g_fat_buffer[g_read_index++];
g_pulse_length |= ((unsigned long) g_fat_buffer[g_read_index++]) << 8;
g_pulse_length |= ((unsigned long) g_fat_buffer[g_read_index++]) << 16;
g_tap_file_pos++;
} else { // otherwise we have a 24 bit pulse value, read it from the buffer
g_pulse_length = (uint32_t) g_fat_buffer[g_read_index++];
g_pulse_length |= ((uint32_t) g_fat_buffer[g_read_index++]) << 8;
g_pulse_length |= ((uint32_t) g_fat_buffer[g_read_index++]) << 16;
g_pulse_length *= g_cycle_mult_raw;
g_tap_file_pos += 3;
}

if (g_tap_info.version != 2) {
g_pulse_length_save = g_pulse_length; // save this for the 2nd half of the wave
} else {
// format 2 is half-wave and timer is running at 2Mhz so double
g_pulse_length <<= 1;
// now read second half-wave for C16 / Plus4 format
tap_data = (unsigned long) g_fat_buffer[g_read_index++];
g_tap_file_pos++;
if (tap_data != 0) {
g_pulse_length_save = tap_data * g_cycle_mult_8;
} else {
g_pulse_length_save = (unsigned long) g_fat_buffer[g_read_index++];
g_pulse_length_save |= ((unsigned long) g_fat_buffer[g_read_index++]) << 8;
g_pulse_length_save |= ((unsigned long) g_fat_buffer[g_read_index++]) << 16;
g_pulse_length_save *= g_cycle_mult_raw;
g_tap_file_pos += 3;
}
// format 2 is half-wave and timer is running at 2Mhz so double
g_pulse_length_save <<= 1;
}

if (g_pulse_length > 0xFFFF) { // check to see if its bigger than 16 bits
g_pulse_length -= 0xFFFF;
OCR1A = 0xFFFF;
if (g_tap_info.version == 2) {
g_pulse_length <<= 1; // TAP v2 format is half-wave and the timer is running at 2Mhz so double the value
} else {
OCR1A = (unsigned short) g_pulse_length;
g_pulse_length = g_pulse_length_save; // restore pulse length for the 2nd half of the signal
g_signal_2nd_half = 1; // next time round switch to 2nd half
}
if (g_invert_signal) {
TAPE_READ_HIGH(); // set the signal high
} else {
TAPE_READ_LOW(); // set the signal high
g_pulse_length_save = g_pulse_length; // otherwise save the pulse length for the 2nd half of a v0 or v1 wave
}
}
}

// Set output signal. The wave transition is HIGH->LOW for the 1st half of the signal, LOW->HIGH for the 2nd half of the signal
// if the signal is inverted we have the opposite condition
//
if (g_invert_signal ^ g_signal_2nd_half) {
TAPE_READ_HIGH(); // set the signal high
} else {
TAPE_READ_LOW(); // set the signal low
}

// Set timer
if (g_pulse_length > 0xFFFF) { // check to see if its bigger than 16 bits
g_pulse_length -= 0xFFFF;
OCR1A = 0xFFFF;
} else {
OCR1A = (unsigned short) g_pulse_length;
g_pulse_length = 0;
g_signal_2nd_half = !g_signal_2nd_half; // Flag that we will be processing the 2nd half of the signal next time the interrupt occurs
}
}


ISR(TIMER2_COMPA_vect) {
disk_timerproc(); // Drive timer procedure for FatFs low level disk I/O module
input_callback();
Expand Down Expand Up @@ -390,7 +366,7 @@ int play_file(FILINFO* pfile_info)
return 0;
}

// br is tested by verify_tap() to be at least FAT_BUF_SIZE (we've read at least FAT_BUF_SIZE from the TAP file)
// verify_tap() has read the full buffer (FAT_BUF_SIZE) into g_fat_buffer (or failed).
UINT br = FAT_BUF_SIZE;

// setup all start conditions
Expand All @@ -399,6 +375,8 @@ int play_file(FILINFO* pfile_info)
g_tap_file_pos = 0;
g_signal_2nd_half = 0;
g_is_paused = 0;
g_pulse_length = 0;
g_pulse_length_save = 0;

lcd_title_P(S_LOADING);

Expand Down
2 changes: 1 addition & 1 deletion version.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
#define VERSION_H

#define TAPUINO_MAJOR_VERSION 2
#define TAPUINO_MINOR_VERSION 9
#define TAPUINO_MINOR_VERSION 10
#define TAPUINO_BUILD_VERSION 0

#endif

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