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Took a first, incorrect, shot at TZX chunk 0x19, the generalised data block.

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This commit is contained in:
Thomas Harte 2017-07-16 22:40:38 -04:00
parent 7327da6350
commit b63971caf7
2 changed files with 89 additions and 1 deletions
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87
Storage/Tape/Formats/TZX.cpp
View File

@ -10,6 +10,10 @@
using namespace Storage::Tape;
namespace {
const unsigned int StandardTZXClock = 3500000;
}
TZX::TZX(const char *file_name) :
Storage::FileHolder(file_name),
is_high_(false) {
@ -31,8 +35,89 @@ TZX::TZX(const char *file_name) :
void TZX::virtual_reset() {
clear();
fseek(file_, SEEK_SET, 0x0a);
fseek(file_, 0x0a, SEEK_SET);
}
void TZX::get_next_pulses() {
while(empty()) {
uint8_t chunk_id = (uint8_t)fgetc(file_);
if(feof(file_)) {
set_is_at_end(true);
return;
}
switch(chunk_id) {
case 0x19: get_generalised_data_block(); break;
case 0x30: {
// Text description. Ripe for ignoring.
int length = fgetc(file_);
fseek(file_, length, SEEK_CUR);
} break;
default:
// In TZX each chunk has a different way of stating or implying its length,
// so there is no route past an unimplemented chunk.
printf("!!Unknown %02x!!", chunk_id);
set_is_at_end(true);
return;
}
}
}
void TZX::get_generalised_data_block() {
uint32_t block_length = fgetc32le();
uint16_t pause_after_block = fgetc16le();
uint32_t total_pilot_symbols = fgetc32le();
uint8_t maximum_pulses_per_pilot_symbol = (uint8_t)fgetc(file_);
uint8_t symbols_in_pilot_table = (uint8_t)fgetc(file_);
uint32_t total_data_symbols = fgetc32le();
uint8_t maximum_pulses_per_data_symbol = (uint8_t)fgetc(file_);
uint8_t symbols_in_data_table = (uint8_t)fgetc(file_);
get_generalised_segment(total_pilot_symbols, maximum_pulses_per_pilot_symbol, symbols_in_pilot_table);
get_generalised_segment(total_data_symbols, maximum_pulses_per_data_symbol, symbols_in_data_table);
emplace_back(Tape::Pulse::Zero, Storage::Time((unsigned int)pause_after_block, 1000u));
}
void TZX::get_generalised_segment(uint32_t output_symbols, uint8_t max_pulses_per_symbol, uint8_t number_of_symbols) {
if(!output_symbols) return;
// Construct the symbol table.
struct Symbol {
uint8_t flags;
std::vector<uint16_t> pulse_lengths;
};
std::vector<Symbol> symbol_table;
for(int c = 0; c < number_of_symbols; c++) {
Symbol symbol;
symbol.flags = (uint8_t)fgetc(file_);
for(int ic = 0; ic < max_pulses_per_symbol; ic++) {
symbol.pulse_lengths.push_back(fgetc16le());
}
}
// Hence produce the output.
for(int c = 0; c < output_symbols; c++) {
uint8_t symbol_value = (uint8_t)fgetc(file_);
Symbol &symbol = symbol_table[symbol_value];
// Mutate initial output level.
switch(symbol.flags & 3) {
case 0: break;
case 1: is_high_ ^= true; break;
case 2: is_high_ = true; break;
case 3: is_high_ = false; break;
}
// Output waves.
for(auto length : symbol.pulse_lengths) {
if(!length) break;
is_high_ ^= true;
emplace_back(is_high_ ? Tape::Pulse::High : Tape::Pulse::Low, Storage::Time((unsigned int)length, StandardTZXClock));
}
}
}

3
Storage/Tape/Formats/TZX.hpp
View File

@ -36,6 +36,9 @@ class TZX: public PulseQueuedTape, public Storage::FileHolder {
void get_next_pulses();
bool is_high_;
void get_generalised_data_block();
void get_generalised_segment(uint32_t output_symbols, uint8_t max_pulses_per_symbol, uint8_t number_of_symbols);
};
}