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CLK/Storage/Tape/Formats/TapePRG.cpp
2018-05-13 15:43:03 -04:00

211 lines
6.1 KiB
C++

//
// TapePRG.cpp
// Clock Signal
//
// Created by Thomas Harte on 14/08/2016.
// Copyright 2016 Thomas Harte. All rights reserved.
//
#include "TapePRG.hpp"
/*
My interpretation of Commodore's tape format is such that a PRG is encoded as:
[long block of lead-in tone]
[short block of lead-in tone]
[count down][header; 192 bytes fixed length]
[short block of lead-in tone]
[count down][copy of header; 192 bytes fixed length]
[gap]
[short block of lead-in tone]
[count down][data; length as in file]
[short block of lead-in tone]
[count down][copy of data]
... and repeat ...
Individual bytes are composed of:
word marker
least significant bit
...
most significant bit
parity bit
Both the header and data blocks additionally end with an end-of-block marker.
Encoding is via square-wave cycles of four lengths, in ascending order: lead-in, zero, one, marker.
Lead-in tone is always just repetitions of the lead-in wave.
A word marker is a marker wave followed by a one wave.
An end-of-block marker is a marker wave followed by a zero wave.
A zero bit is a zero wave followed by a one wave.
A one bit is a one wave followed by a zero wave.
Parity is 1 if there are an even number of bits in the byte; 0 otherwise.
*/
#include <sys/stat.h>
using namespace Storage::Tape;
PRG::PRG(const std::string &file_name) :
file_(file_name)
{
// There's really no way to validate other than that if this file is larger than 64kb,
// of if load address + length > 65536 then it's broken.
if(file_.stats().st_size >= 65538 || file_.stats().st_size < 3)
throw ErrorBadFormat;
load_address_ = file_.get16le();
length_ = static_cast<uint16_t>(file_.stats().st_size - 2);
if (load_address_ + length_ >= 65536)
throw ErrorBadFormat;
}
Storage::Tape::Tape::Pulse PRG::virtual_get_next_pulse() {
// these are all microseconds per pole
static const unsigned int leader_zero_length = 179;
static const unsigned int zero_length = 169;
static const unsigned int one_length = 247;
static const unsigned int marker_length = 328;
bit_phase_ = (bit_phase_+1)&3;
if(!bit_phase_) get_next_output_token();
Tape::Pulse pulse;
pulse.length.clock_rate = 1000000;
pulse.type = (bit_phase_&1) ? Tape::Pulse::High : Tape::Pulse::Low;
switch(output_token_) {
case Leader: pulse.length.length = leader_zero_length; break;
case Zero: pulse.length.length = (bit_phase_&2) ? one_length : zero_length; break;
case One: pulse.length.length = (bit_phase_&2) ? zero_length : one_length; break;
case WordMarker: pulse.length.length = (bit_phase_&2) ? one_length : marker_length; break;
case EndOfBlock: pulse.length.length = (bit_phase_&2) ? zero_length : marker_length; break;
case Silence: pulse.type = Tape::Pulse::Zero; pulse.length.length = 5000; break;
}
return pulse;
}
void PRG::virtual_reset() {
bit_phase_ = 3;
file_.seek(2, SEEK_SET);
file_phase_ = FilePhaseLeadIn;
phase_offset_ = 0;
copy_mask_ = 0x80;
}
bool PRG::is_at_end() {
return file_phase_ == FilePhaseAtEnd;
}
void PRG::get_next_output_token() {
static const int block_length = 192; // not counting the checksum
static const int countdown_bytes = 9;
static const int leadin_length = 20000;
static const int block_leadin_length = 5000;
if(file_phase_ == FilePhaseHeaderDataGap || file_phase_ == FilePhaseAtEnd) {
output_token_ = Silence;
if(file_phase_ != FilePhaseAtEnd) file_phase_ = FilePhaseData;
return;
}
// the lead-in is 20,000 instances of the lead-in pair; every other phase begins with 5000
// before doing whatever it should be doing
if(file_phase_ == FilePhaseLeadIn || phase_offset_ < block_leadin_length) {
output_token_ = Leader;
phase_offset_++;
if(file_phase_ == FilePhaseLeadIn && phase_offset_ == leadin_length) {
phase_offset_ = 0;
file_phase_ = (file_phase_ == FilePhaseLeadIn) ? FilePhaseHeader : FilePhaseData;
}
return;
}
// determine whether a new byte needs to be queued up
int block_offset = phase_offset_ - block_leadin_length;
int bit_offset = block_offset % 10;
int byte_offset = block_offset / 10;
phase_offset_++;
if(!bit_offset &&
(
(file_phase_ == FilePhaseHeader && byte_offset == block_length + countdown_bytes + 1) ||
file_.eof()
)
) {
output_token_ = EndOfBlock;
phase_offset_ = 0;
switch(file_phase_) {
default: break;
case FilePhaseHeader:
copy_mask_ ^= 0x80;
if(copy_mask_) file_phase_ = FilePhaseHeaderDataGap;
break;
case FilePhaseData:
copy_mask_ ^= 0x80;
file_.seek(2, SEEK_SET);
if(copy_mask_) file_phase_ = FilePhaseAtEnd;
break;
}
return;
}
if(bit_offset == 0) {
// the first nine bytes are countdown; the high bit is set if this is a header
if(byte_offset < countdown_bytes) {
output_byte_ = static_cast<uint8_t>(countdown_bytes - byte_offset) | copy_mask_;
} else {
if(file_phase_ == FilePhaseHeader) {
if(byte_offset == countdown_bytes + block_length) {
output_byte_ = check_digit_;
} else {
if(byte_offset == countdown_bytes) check_digit_ = 0;
if(file_phase_ == FilePhaseHeader) {
switch(byte_offset - countdown_bytes) {
case 0: output_byte_ = 0x03; break;
case 1: output_byte_ = load_address_ & 0xff; break;
case 2: output_byte_ = (load_address_ >> 8)&0xff; break;
case 3: output_byte_ = (load_address_ + length_) & 0xff; break;
case 4: output_byte_ = ((load_address_ + length_) >> 8) & 0xff; break;
case 5: output_byte_ = 0x50; break; // P
case 6: output_byte_ = 0x52; break; // R
case 7: output_byte_ = 0x47; break; // G
default:
output_byte_ = 0x20;
break;
}
}
}
} else {
output_byte_ = file_.get8();
if(file_.eof()) {
output_byte_ = check_digit_;
}
}
check_digit_ ^= output_byte_;
}
}
switch(bit_offset) {
case 0:
output_token_ = WordMarker;
break;
default: // i.e. 1-8
output_token_ = (output_byte_ & (1 << (bit_offset - 1))) ? One : Zero;
break;
case 9: {
uint8_t parity = output_byte_;
parity ^= (parity >> 4);
parity ^= (parity >> 2);
parity ^= (parity >> 1);
output_token_ = (parity&1) ? Zero : One;
}
break;
}
}