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Speeds up byte decoding within sectors for the ahead-of-time MFM parser.

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Thomas Harte 2017-09-16 20:28:24 -04:00
parent 5fbea625ae
commit 44a56724cb
1 changed files with 10 additions and 2 deletions
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12
Storage/Disk/Encodings/MFM.cpp
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@ -221,7 +221,7 @@ std::shared_ptr<Storage::Disk::Track> Storage::Encodings::MFM::GetMFMTrackWithSe
22, 0x4e,
12,
(sector_gap_length != DefaultSectorGapLength) ? sector_gap_length : 54, 0xff,
12500); // unintelligently: double the single-density bytes/rotation (or: 500kps @ 300 rpm)
12500); // unintelligently: double the single-density bytes/rotation (or: 500kbps @ 300 rpm)
}
std::unique_ptr<Encoder> Storage::Encodings::MFM::GetMFMEncoder(std::vector<uint8_t> &target) {
@ -337,7 +337,15 @@ uint8_t Parser::get_byte_for_shift_value(uint16_t value) {
uint8_t Parser::get_next_byte() {
bit_count_ = 0;
while(bit_count_ < 16) run_for(Cycles(1));
// Archetypal MFM is 500,000 bps given that the drive has an RPM of 300. Clock rate was
// specified at 4,000,000. So that's an idealised 8 cycles per bit, Jump ahead 14
// times that...
run_for(Cycles(14 * 8));
// ... and proceed at half-idealised-bit intervals to get the next bit. Then proceed very gingerly indeed.
while(bit_count_ < 15) run_for(Cycles(4));
while(bit_count_ < 16) run_for(Cycles(2));
uint8_t byte = get_byte_for_shift_value((uint16_t)shift_register_);
crc_generator_.add(byte);
return byte;