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Eliminated false register aliasing, restricted register sizes and locked out reading and writing where appropriate.

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This commit is contained in:
Thomas Harte 2017-08-10 11:22:30 -04:00
parent b1dbd7833a
commit be8e7a4144
1 changed files with 10 additions and 3 deletions
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13
Components/6845/CRTC6845.hpp
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@ -138,7 +138,7 @@ template <class T> class CRTC6845 {
} }
void select_register(uint8_t r) { void select_register(uint8_t r) {
selected_register_ = (int)r & 15; selected_register_ = r;
} }
uint8_t get_status() { uint8_t get_status() {
@ -146,18 +146,25 @@ template <class T> class CRTC6845 {
} }
uint8_t get_register() { uint8_t get_register() {
if(selected_register_ < 12 || selected_register_ > 17) return 0xff;
return registers_[selected_register_]; return registers_[selected_register_];
} }
void set_register(uint8_t value) { void set_register(uint8_t value) {
registers_[selected_register_] = value; static uint8_t masks[] = {
0xff, 0xff, 0xff, 0xff, 0x7f, 0x1f, 0x7f, 0x7f,
0xff, 0x1f, 0x7f, 0x1f, 0x3f, 0xff, 0x3f, 0xff
};
if(selected_register_ < 16)
registers_[selected_register_] = value & masks[selected_register_];
} }
private: private:
T &bus_handler_; T &bus_handler_;
BusState bus_state_; BusState bus_state_;
uint8_t registers_[16]; uint8_t registers_[18];
int selected_register_; int selected_register_;
uint8_t character_counter_; uint8_t character_counter_;