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Refactors the 6845 more clearly to break out the acts of ending a line and ending a frame, changing the way the memory address is altered — the end-of-line value is provisionally stored and then used if necessary — in order to do so.

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This commit is contained in:
Thomas Harte 2017-08-22 21:54:48 -04:00
parent 8afd83b91f
commit e956740c56
1 changed files with 105 additions and 100 deletions
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205
Components/6845/CRTC6845.hpp
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@ -44,106 +44,6 @@ template <class T> class CRTC6845 {
CRTC6845(Personality p, T &bus_handler) :
personality_(p), bus_handler_(bus_handler) {}
void run_for(Cycles cycles) {
int cyles_remaining = cycles.as_int();
while(cyles_remaining--) {
// check for end of horizontal sync
if(hsync_down_counter_) {
hsync_down_counter_--;
if(!hsync_down_counter_) {
bus_state_.hsync = false;
}
}
// check for end of line
bool is_end_of_line = character_counter_ == registers_[0];
// increment counter
character_counter_++;
// check for start of horizontal sync
if(character_counter_ == registers_[2]) {
hsync_down_counter_ = registers_[3] & 15;
if(hsync_down_counter_) bus_state_.hsync = true;
}
// update refresh address
if(character_is_visible_) {
bus_state_.refresh_address++;
}
// check for end of visible characters
if(character_counter_ == registers_[1]) {
character_is_visible_ = false;
}
// check for end-of-line
if(is_end_of_line) {
// check for end of vertical sync
if(vsync_down_counter_) {
vsync_down_counter_--;
if(!vsync_down_counter_) {
bus_state_.vsync = false;
}
}
if(is_in_adjustment_period_) {
line_counter_++;
if(line_counter_ == registers_[5]) {
line_counter_ = 0;
is_in_adjustment_period_ = false;
line_is_visible_ = true;
line_address_ = (uint16_t)((registers_[12] << 8) | registers_[13]);
bus_state_.refresh_address = line_address_;
}
} else {
// advance vertical counter
if(bus_state_.row_address == registers_[9]) {
if(!character_is_visible_)
line_address_ = bus_state_.refresh_address;
bus_state_.row_address = 0;
bool is_at_end_of_frame = line_counter_ == registers_[4];
line_counter_ = (line_counter_ + 1) & 0x7f;
// check for end of visible lines
if(line_counter_ == registers_[6]) {
line_is_visible_ = false;
}
// check for start of vertical sync
if(line_counter_ == registers_[7]) {
bus_state_.vsync = true;
vsync_down_counter_ = registers_[3] >> 4;
if(!vsync_down_counter_) vsync_down_counter_ = 16;
}
// check for entry into the overflow area
if(is_at_end_of_frame) {
if(registers_[5]) {
is_in_adjustment_period_ = true;
} else {
line_is_visible_ = true;
line_address_ = (uint16_t)((registers_[12] << 8) | registers_[13]);
bus_state_.refresh_address = line_address_;
}
bus_state_.row_address = 0;
line_counter_ = 0;
}
} else {
bus_state_.row_address = (bus_state_.row_address + 1) & 0x1f;
}
bus_state_.refresh_address = line_address_;
}
character_counter_ = 0;
character_is_visible_ = (registers_[1] != 0);
}
perform_bus_cycle();
}
}
void select_register(uint8_t r) {
selected_register_ = r;
}
@ -172,6 +72,48 @@ template <class T> class CRTC6845 {
registers_[16] = bus_state_.refresh_address >> 8;
}
void run_for(Cycles cycles) {
static int c = 0;
c++;
int cyles_remaining = cycles.as_int();
while(cyles_remaining--) {
// check for end of horizontal sync
if(hsync_down_counter_) {
hsync_down_counter_--;
if(!hsync_down_counter_) {
bus_state_.hsync = false;
}
}
// check for start of horizontal sync
if(character_counter_ == registers_[2]) {
hsync_down_counter_ = registers_[3] & 15;
if(hsync_down_counter_) bus_state_.hsync = true;
}
// check for end of visible characters
if(character_counter_ == registers_[1]) {
// TODO: consider skew in character_is_visible_. Or maybe defer until perform_bus_cycle?
character_is_visible_ = false;
end_of_line_address_ = bus_state_.refresh_address;
}
perform_bus_cycle();
bus_state_.refresh_address++;
// check for end-of-line
if(character_counter_ == registers_[0]) {
character_counter_ = 0;
do_end_of_line();
character_is_visible_ = true;
} else {
// increment counter
character_counter_++;
}
}
}
private:
inline void perform_bus_cycle() {
bus_state_.display_enable = character_is_visible_ && line_is_visible_;
@ -179,6 +121,67 @@ template <class T> class CRTC6845 {
bus_handler_.perform_bus_cycle(bus_state_);
}
inline void do_end_of_line() {
// check for end of vertical sync
if(vsync_down_counter_) {
vsync_down_counter_--;
if(!vsync_down_counter_) {
bus_state_.vsync = false;
}
}
if(is_in_adjustment_period_) {
line_counter_++;
if(line_counter_ == registers_[5]) {
is_in_adjustment_period_ = false;
do_end_of_frame();
}
} else {
// advance vertical counter
if(bus_state_.row_address == registers_[9]) {
bus_state_.row_address = 0;
line_address_ = end_of_line_address_;
// check for entry into the overflow area
if(line_counter_ == registers_[4]) {
if(registers_[5]) {
line_counter_ = 0;
is_in_adjustment_period_ = true;
} else {
do_end_of_frame();
}
} else {
line_counter_ = (line_counter_ + 1) & 0x7f;
// check for end of visible lines
if(line_counter_ == registers_[6]) {
line_is_visible_ = false;
}
// check for start of vertical sync
if(line_counter_ == registers_[7]) {
bus_state_.vsync = true;
vsync_down_counter_ = registers_[3] >> 4;
if(!vsync_down_counter_) vsync_down_counter_ = 16;
}
}
} else {
bus_state_.row_address = (bus_state_.row_address + 1) & 0x1f;
}
}
bus_state_.refresh_address = line_address_;
character_counter_ = 0;
character_is_visible_ = (registers_[1] != 0);
}
inline void do_end_of_frame() {
line_counter_ = 0;
line_is_visible_ = true;
line_address_ = (uint16_t)((registers_[12] << 8) | registers_[13]);
bus_state_.refresh_address = line_address_;
}
Personality personality_;
T &bus_handler_;
BusState bus_state_;
@ -194,7 +197,9 @@ template <class T> class CRTC6845 {
int hsync_down_counter_;
int vsync_down_counter_;
bool is_in_adjustment_period_;
uint16_t line_address_;
uint16_t end_of_line_address_;
};
}