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Ensured that the final bit of a tape isn't dropped even if the tape ends exactly after it, by not posting a false pulse, being less restrictive about what can cap a bit, and in any case using a long gap as the end-of-file bookend.

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This commit is contained in:
Thomas Harte 2017-07-22 15:41:33 -04:00
parent 456fdda6c2
commit 313b36944f
1 changed files with 7 additions and 12 deletions
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19
Storage/Tape/Parsers/ZX8081.cpp
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@ -45,10 +45,8 @@ void Parser::post_pulse() {
}
void Parser::mark_end() {
// Push the last thing detected, and post an 'unrecognised' to ensure
// the queue empties out.
post_pulse();
push_wave(WaveType::Unrecognised);
// Post a long gap to cap any bit that's in the process of recognition.
push_wave(WaveType::LongGap);
}
void Parser::inspect_waves(const std::vector<WaveType> &waves) {
@ -76,14 +74,11 @@ void Parser::inspect_waves(const std::vector<WaveType> &waves) {
number_of_pulses++;
}
// If those pulses were followed by a gap then they might be
// a recognised symbol.
if(number_of_pulses + wave_offset < waves.size() &&
(waves[number_of_pulses + wave_offset] == WaveType::LongGap || waves[number_of_pulses + wave_offset] == WaveType::Gap)) {
// A 1 is 18 up/down waves, a 0 is 8. But the final down will be indistinguishable from
// the gap that follows the bit due to the simplified "high is high, everything else is low"
// logic applied to pulse detection. So those two things will merge. Meaning we're looking for
// 17 and/or 7 pulses.
// If those pulses were followed by something not recognised as a pulse, check for a bit
if(number_of_pulses + wave_offset < waves.size()) {
// A 1 is 9 waves, a 0 is 4. Counting upward zero transitions, the first in either group will
// act simply to terminate the gap beforehand and won't be logged as a pulse. So counts to
// check are 8 and 3.
size_t gaps_to_swallow = wave_offset + ((waves[number_of_pulses + wave_offset] == WaveType::Gap) ? 1 : 0);
switch(number_of_pulses) {
case 8: push_symbol(SymbolType::One, (int)(number_of_pulses + gaps_to_swallow)); break;