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Started making some formal admissions that different CRTC models exist. Plenty yet to do.

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This commit is contained in:
Thomas Harte 2017-08-27 18:10:07 -04:00
parent 0ced7866fc
commit 113349d272
1 changed files with 41 additions and 9 deletions
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46
Components/6845/CRTC6845.hpp
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@ -44,27 +44,38 @@ class BusHandler {
};
enum Personality {
HD6845S, //
UM6845R, //
MC6845, //
AMS40226 //
HD6845S, // Type 0 in CPC parlance. Zero-width HSYNC available, no status, programmable VSYNC length.
UM6845R, // Type 1 in CPC parlance. Status register, fixed-length VSYNC.
MC6845, // Type 2. No status register, fixed-length VSYNC, no zero-length HSYNC.
AMS40226 // Type 3. Status is get register, fixed-length VSYNC, no zero-length HSYNC.
};
// TODO UM6845R and R12/R13; see http://www.cpcwiki.eu/index.php/CRTC#CRTC_Differences
template <class T> class CRTC6845 {
public:
CRTC6845(Personality p, T &bus_handler) noexcept :
personality_(p), bus_handler_(bus_handler) {}
personality_(p), bus_handler_(bus_handler), status_(0) {}
void select_register(uint8_t r) {
selected_register_ = r;
}
uint8_t get_status() const {
switch(personality_) {
case UM6845R: return status_ | (bus_state_.vsync ? 0x20 : 0x00);
case AMS40226: return get_register();
default: return 0xff;
}
return 0xff;
}
uint8_t get_register() const {
if(selected_register_ == 31) status_ &= ~0x80;
if(selected_register_ == 16 || selected_register_ == 17) status_ &= ~0x40;
if(personality_ == UM6845R && selected_register_ == 31) return dummy_register_;
if(selected_register_ < 12 || selected_register_ > 17) return 0xff;
return registers_[selected_register_];
}
@ -78,11 +89,15 @@ template <class T> class CRTC6845 {
if(selected_register_ < 16) {
registers_[selected_register_] = value & masks[selected_register_];
}
if(selected_register_ == 31 && personality_ == UM6845R) {
dummy_register_ = value;
}
}
void trigger_light_pen() {
registers_[17] = bus_state_.refresh_address & 0xff;
registers_[16] = bus_state_.refresh_address >> 8;
status_ |= 0x40;
}
void run_for(Cycles cycles) {
@ -117,8 +132,17 @@ template <class T> class CRTC6845 {
// check for end of horizontal sync; note that a sync time of zero will result in an immediate
// cancellation of the plan to perform sync
if(bus_state_.hsync) {
switch(personality_) {
case HD6845S:
case UM6845R:
bus_state_.hsync = hsync_counter_ != (registers_[3] & 15);
hsync_counter_ = (hsync_counter_ + 1) & 15;
break;
default:
hsync_counter_ = (hsync_counter_ + 1) & 15;
bus_state_.hsync = hsync_counter_ != (registers_[3] & 15);
break;
}
}
perform_bus_cycle_phase2();
@ -144,8 +168,14 @@ template <class T> class CRTC6845 {
// check for end of vertical sync
if(bus_state_.vsync) {
vsync_counter_ = (vsync_counter_ + 1) & 15;
if(vsync_counter_ == (registers_[3] >> 4)) {
bus_state_.vsync = false;
switch(personality_) {
case HD6845S:
case AMS40226:
bus_state_.vsync = vsync_counter_ != (registers_[3] >> 4);
break;
default:
bus_state_.vsync = vsync_counter_ != 0;
break;
}
}
@ -205,6 +235,7 @@ template <class T> class CRTC6845 {
BusState bus_state_;
uint8_t registers_[18];
uint8_t dummy_register_;
int selected_register_;
uint8_t character_counter_;
@ -218,6 +249,7 @@ template <class T> class CRTC6845 {
uint16_t line_address_;
uint16_t end_of_line_address_;
uint8_t status_;
};
}