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I'm starting to make a little headway, I think: this performs lead-ins and countdowns, though with no actual data or anything as helpful as that.

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This commit is contained in:
Thomas Harte 2016-08-15 22:10:53 -04:00
parent 7e2b4554ea
commit 7994148f55
2 changed files with 57 additions and 4 deletions
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54
Storage/Tape/Formats/TapePRG.cpp
View File

@ -12,7 +12,7 @@
using namespace Storage;
TapePRG::TapePRG(const char *file_name) : _file(nullptr), _bitPhase(3)
TapePRG::TapePRG(const char *file_name) : _file(nullptr), _bitPhase(3), _filePhase(FilePhaseLeadIn), _phaseOffset(0)
{
struct stat file_stats;
stat(file_name, &file_stats);
@ -64,9 +64,59 @@ void TapePRG::reset()
{
_bitPhase = 3;
fseek(_file, 2, SEEK_SET);
_filePhase = FilePhaseLeadIn;
_phaseOffset = 0;
}
void TapePRG::get_next_output_token()
{
_outputToken = Leader;
// 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(_filePhase == FilePhaseLeadIn || _phaseOffset < 5000)
{
_outputToken = Leader;
_phaseOffset++;
if(_filePhase == FilePhaseLeadIn && _phaseOffset == 20000)
{
_phaseOffset = 0;
_filePhase = FilePhaseHeader;
}
return;
}
// determine whether a new byte needs to be queued up
int block_offset = _phaseOffset - 5000;
int bit_offset = block_offset % 10;
int byte_offset = block_offset / 10;
if(bit_offset == 0)
{
// the first nine bytes are countdown; the high bit is set if this is a header
if(byte_offset < 9)
{
_output_byte = (uint8_t)(9 - block_offset) | 0x80;
}
else
{
}
}
switch(bit_offset)
{
case 0:
_outputToken = WordMarker;
break;
default:
_outputToken = (_output_byte & (1 << (bit_offset - 1))) ? One : Zero;
break;
case 1:
{
uint8_t parity = _outputToken;
parity ^= (parity >> 4);
parity ^= (parity >> 2);
parity ^= (parity >> 1);
_outputToken = (parity&1) ? One : Zero;
}
break;
}
}

7
Storage/Tape/Formats/TapePRG.hpp
View File

@ -42,17 +42,20 @@ class TapePRG: public Tape {
enum FilePhase {
FilePhaseLeadIn,
FilePhaseHeader
FilePhaseHeader,
FilePhaseData,
} _filePhase;
int _phaseOffset;
int _bitPhase;
enum OutputToken {
Leader,
Zero,
One,
WordMarker
WordMarker,
} _outputToken;
void get_next_output_token();
uint8_t _output_byte;
};
}