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Ensures delayed loading isn't interrupted by blank, hsync.

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This commit is contained in:
Thomas Harte 2019-12-12 23:20:28 -05:00
parent f6f2b4b90f
commit 4bcf217324
2 changed files with 37 additions and 15 deletions
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46
Machines/Atari/ST/Video.cpp
View File

@ -169,6 +169,28 @@ void Video::run_for(HalfCycles duration) {
const int run_length = std::min(integer_duration, next_event - x_);
const bool display_enable = vertical_.enable && horizontal_.enable;
// Ensure proper fetching irrespective of the output.
if(load_) {
const int since_load = x_ - load_base_;
// There will be pixels this line, subject to the shifter pipeline.
// Divide into 8-[half-]cycle windows; at the start of each window fetch a word,
// and during the rest of the window, shift out.
int start_column = since_load >> 3;
const int end_column = (since_load + run_length) >> 3;
while(start_column != end_column) {
data_latch_[data_latch_position_] = ram_[current_address_ & 262143];
data_latch_position_ = (data_latch_position_ + 1) & 127;
++current_address_;
++start_column;
}
}
// TODO: if I'm asserting that sync and blank override the shifter (but, presumably,
// the shifter keeps shifting), then output_sync and output_blank need to have an effect
// inside the shifter on the temporary register values.
if(horizontal_.sync || vertical_.sync) {
shifter_.output_sync(run_length);
} else if(horizontal_.blank || vertical_.blank) {
@ -198,14 +220,14 @@ void Video::run_for(HalfCycles duration) {
// If at least one column boundary is crossed, complete this column.
shifter_.output_pixels(8 - (since_load & 7), output_bpp_);
++start_column; // This starts a new column, so latch a new word.
latch_word();
push_latched_data();
}
// Run for all columns that have their starts in this time period.
int complete_columns = end_column - start_column;
while(complete_columns--) {
shifter_.output_pixels(8, output_bpp_);
latch_word();
push_latched_data();
}
// Output the start of the next column, if necessary.
@ -295,23 +317,21 @@ void Video::run_for(HalfCycles duration) {
}
}
void Video::latch_word() {
data_latch_[data_latch_position_] = ram_[current_address_ & 262143];
++current_address_;
++data_latch_position_;
if(data_latch_position_ == 4) {
data_latch_position_ = 0;
void Video::push_latched_data() {
data_latch_read_position_ = (data_latch_read_position_ + 1) & 127;
if(!(data_latch_read_position_ & 3)) {
shifter_.load(
(uint64_t(data_latch_[0]) << 48) |
(uint64_t(data_latch_[1]) << 32) |
(uint64_t(data_latch_[2]) << 16) |
uint64_t(data_latch_[3])
(uint64_t(data_latch_[(data_latch_read_position_ - 4) & 127]) << 48) |
(uint64_t(data_latch_[(data_latch_read_position_ - 3) & 127]) << 32) |
(uint64_t(data_latch_[(data_latch_read_position_ - 2) & 127]) << 16) |
uint64_t(data_latch_[(data_latch_read_position_ - 1) & 127])
);
}
}
void Video::reset_fifo() {
data_latch_position_ = 0;
data_latch_read_position_ = data_latch_position_ = 0;
}
bool Video::hsync() {

6
Machines/Atari/ST/Video.hpp
View File

@ -151,8 +151,10 @@ class Video {
int line_length_ = 1024;
int data_latch_position_ = 0;
uint16_t data_latch_[4] = {0, 0, 0, 0};
void latch_word();
int data_latch_read_position_ = 0;
uint16_t data_latch_[128];
void push_latched_data();
void reset_fifo();
class Shifter {