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Makes a genuine attempt at real line counting.

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No output yet though.
This commit is contained in:
Thomas Harte 2021-06-15 18:57:14 -04:00
parent 90b8163d54
commit 60cf8486bb
2 changed files with 67 additions and 2 deletions
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60
Machines/Enterprise/Nick.cpp
View File

@ -36,8 +36,13 @@ void Nick::write(uint16_t address, uint8_t value) {
// Still a mystery to me: the exact meaning of the top two bits here. For now
// just treat a 0 -> 1 transition of the MSB as a forced frame restart.
if((value^line_parameter_control_) & value & 0x80) {
// TODO: restart frame.
printf("Should restart frame from %04x\n", line_parameter_base_);
// For now: just force this to be the final line of this mode block.
// I'm unclear whether I should also reset the horizontal counter
// (i.e. completely abandon current video phase).
lines_remaining_ = 0xff;
line_parameters_[1] |= 1;
}
line_parameter_control_ = value & 0xc0;
break;
@ -48,7 +53,58 @@ uint8_t Nick::read([[maybe_unused]] uint16_t address) {
return 0xff;
}
void Nick::run_for(HalfCycles) {
void Nick::run_for(HalfCycles duration) {
constexpr int line_length = 912;
int clocks_remaining = duration.as<int>();
while(clocks_remaining) {
// Determine how many cycles are left this line.
const int clocks_this_line = std::min(clocks_remaining, line_length - horizontal_counter_);
// Convert that into a [start/current] and end window.
int window = horizontal_counter_ >> 4;
const int end_window = (horizontal_counter_ + clocks_this_line) >> 4;
// Advance the line counters.
clocks_remaining -= clocks_this_line;
horizontal_counter_ = (horizontal_counter_ + clocks_this_line) % line_length;
// Do nothing if a window boundary isn't crossed.
if(window == end_window) continue;
// If this is within the first 8 cycles of the line, [possibly] fetch
// the relevant part of the line parameters.
if(should_reload_line_parameters_ && window < 8) {
int fetch_spot = window;
while(fetch_spot < end_window && fetch_spot < 8) {
line_parameters_[(fetch_spot << 1)] = ram_[line_parameter_pointer_];
line_parameters_[(fetch_spot << 1) + 1] = ram_[line_parameter_pointer_ + 1];
line_parameter_pointer_ += 2;
++fetch_spot;
}
// If all parameters have been loaded, set appropriate fields.
if(fetch_spot == 8) {
should_reload_line_parameters_ = false;
// Set length of mode line.
lines_remaining_ = line_parameters_[0];
}
}
// Check for end of line.
if(!horizontal_counter_) {
++lines_remaining_;
if(!lines_remaining_) {
should_reload_line_parameters_ = true;
// Check for end-of-frame.
if(line_parameters_[1] & 1) {
line_parameter_pointer_ = line_parameter_base_;
}
}
}
}
}
// MARK: - CRT passthroughs.

9
Machines/Enterprise/Nick.hpp
View File

@ -31,9 +31,18 @@ class Nick {
Outputs::CRT::CRT crt_;
const uint8_t *const ram_;
// CPU-provided state.
uint8_t line_parameter_control_ = 0xc0;
uint16_t line_parameter_base_ = 0x0000;
// Ephemerals, related to current video position.
int horizontal_counter_ = 0;
uint16_t line_parameter_pointer_ = 0x0000;
uint8_t line_parameters_[16];
bool should_reload_line_parameters_ = false;
// Current mode line parameters.
uint8_t lines_remaining_ = 0x00;
};