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Adds elementary decoding of VDP accesses.
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@ -27,8 +27,95 @@ void TMS9918::run_for(const Cycles cycles) {
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}
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void TMS9918::set_register(int address, uint8_t value) {
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// Writes to address 0 are writes to the video RAM. Store
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// the value and return.
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if(!(address & 1)) {
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write_phase_ = false;
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read_ahead_buffer_ = value;
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ram_[ram_pointer_ & 16383] = value;
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ram_pointer_++;
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return;
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}
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// Writes to address 1 are performed in pairs; if this is the
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// low byte of a value, store it and wait for the high byte.
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if(!write_phase_) {
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low_write_ = value;
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write_phase_ = true;
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return;
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}
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write_phase_ = false;
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if(value & 0x80) {
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// This is a write to a register.
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switch(value & 7) {
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case 0:
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screen_mode_ = (screen_mode_ & 6) | ((low_write_ & 2) >> 1);
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break;
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case 1:
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blank_screen_ = !!(low_write_ & 0x40);
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generate_interrupts_ = !!(low_write_ & 0x20);
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screen_mode_ = (screen_mode_ & 1) | ((low_write_ & 0x18) >> 3);
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sprites_16x16_ = !!(low_write_ & 0x02);
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sprites_magnified_ = !!(low_write_ & 0x01);
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reevaluate_interrupts();
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break;
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case 2:
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pattern_name_address_ = (low_write_ & 0xf) << 10;
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break;
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case 3:
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colour_table_address_ = low_write_ << 6;
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break;
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case 4:
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pattern_generator_table_address_ = (low_write_ & 0x07) << 11;
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break;
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case 5:
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sprite_attribute_table_address_ = (low_write_ & 0x7f) << 7;
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break;
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case 6:
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sprite_generator_table_address_ = (low_write_ & 0x07) << 11;
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break;
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case 7:
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text_colour_ = low_write_ >> 4;
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background_colour_ = low_write_ & 0xf;
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break;
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}
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} else {
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// This is a write to the RAM pointer.
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ram_pointer_ = static_cast<uint16_t>(low_write_ | (value << 8));
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if(!(value & 0x40)) {
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// Officially a 'read' set, so perform lookahead.
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read_ahead_buffer_ = ram_[ram_pointer_ & 16383];
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ram_pointer_++;
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}
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}
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}
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uint8_t TMS9918::get_register(int address) {
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return 0;
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write_phase_ = false;
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// Reads from address 0 read video RAM, via the read-ahead buffer.
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if(!(address & 1)) {
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uint8_t result = read_ahead_buffer_;
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read_ahead_buffer_ = ram_[ram_pointer_ & 16383];
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ram_pointer_++;
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return result;
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}
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// Reads from address 1 get the status register;
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uint8_t result = status_;
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status_ &= ~(0x80 | 0x20);
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reevaluate_interrupts();
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return result;
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}
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void TMS9918::reevaluate_interrupts() {
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}
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@ -41,6 +41,32 @@ class TMS9918 {
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private:
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std::shared_ptr<Outputs::CRT::CRT> crt_;
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uint16_t ram_[16384];
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uint16_t ram_pointer_ = 0;
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uint8_t read_ahead_buffer_ = 0;
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uint8_t status_ = 0;
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bool write_phase_ = false;
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uint8_t low_write_ = 0;
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// The various register flags.
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int screen_mode_ = 0;
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bool blank_screen_ = true;
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bool sprites_16x16_ = false;
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bool sprites_magnified_ = false;
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bool generate_interrupts_ = false;
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uint16_t pattern_name_address_ = 0;
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uint16_t colour_table_address_ = 0;
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uint16_t pattern_generator_table_address_ = 0;
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uint16_t sprite_attribute_table_address_ = 0;
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uint16_t sprite_generator_table_address_ = 0;
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uint8_t text_colour_ = 0;
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uint8_t background_colour_ = 0;
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void reevaluate_interrupts();
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};
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};
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@ -102,7 +102,6 @@ class ConcreteMachine:
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case CPU::Z80::PartialMachineCycle::Output:
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switch(address & 0xff) {
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case 0x98: case 0x99:
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printf("VDP %d %02x\n", address&1, *cycle.value);
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vdp_->set_register(address, *cycle.value);
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break;
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