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Correct video address generation.

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This commit is contained in:
Thomas Harte
2025-09-17 21:26:13 -04:00
parent 41196a862d
commit 7bba0b82ef
1 changed files with 34 additions and 19 deletions
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53
Machines/Acorn/BBCMicro/BBCMicro.cpp
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@@ -26,6 +26,7 @@
#include "Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
#include "Concurrency/AsyncTaskQueue.hpp"
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
@@ -91,9 +92,9 @@ struct VideoBaseAddress {
void set_video_base(const uint8_t code) {
switch(code) {
case 0b00: video_base_ = 0x4000; break;
case 0b01: video_base_ = 0x5800; break;
case 0b10: video_base_ = 0x6000; break;
case 0b11: video_base_ = 0x3000; break;
case 0b01: video_base_ = 0x6000; break;
case 0b10: video_base_ = 0x3000; break;
case 0b11: video_base_ = 0x5800; break;
}
}
@@ -341,24 +342,38 @@ public:
pixel_pointer_ = pixel_data_ = crt_.begin_data(320, 8);
}
if(pixel_pointer_) {
// Hard coded for Mode 0!
auto address = uint16_t(
(state.refresh_address << 3) |
state.row_address
);
if(address & 0x8000) {
address = (video_base_ + address) & 0x7fff;
uint16_t address;
if(state.refresh_address & (1 << 13)) {
// Teletext address generation mode.
address = uint16_t(
0x3c00 |
((state.refresh_address & 0x800) << 3) |
(state.refresh_address & 0x3ff)
);
// TODO: wraparound?
} else {
address = uint16_t((state.refresh_address << 3) | (state.row_address & 7));
if(address & 0x8000) {
address = (address + video_base_) & 0x7fff;
}
}
// Hard coded from here for Mode 0!
if(state.row_address & 8) {
std::fill(pixel_pointer_, pixel_pointer_+8, 0);
} else {
const auto source = ram_[address];
pixel_pointer_[0] = (source & 0x80) ? 0xff : 0x00;
pixel_pointer_[1] = (source & 0x40) ? 0xff : 0x00;
pixel_pointer_[2] = (source & 0x20) ? 0xff : 0x00;
pixel_pointer_[3] = (source & 0x10) ? 0xff : 0x00;
pixel_pointer_[4] = (source & 0x08) ? 0xff : 0x00;
pixel_pointer_[5] = (source & 0x04) ? 0xff : 0x00;
pixel_pointer_[6] = (source & 0x02) ? 0xff : 0x00;
pixel_pointer_[7] = (source & 0x01) ? 0xff : 0x00;
}
const auto source = ram_[address];
pixel_pointer_[0] = (source & 0x80) ? 0xff : 0x00;
pixel_pointer_[1] = (source & 0x40) ? 0xff : 0x00;
pixel_pointer_[2] = (source & 0x20) ? 0xff : 0x00;
pixel_pointer_[3] = (source & 0x10) ? 0xff : 0x00;
pixel_pointer_[4] = (source & 0x08) ? 0xff : 0x00;
pixel_pointer_[5] = (source & 0x04) ? 0xff : 0x00;
pixel_pointer_[6] = (source & 0x02) ? 0xff : 0x00;
pixel_pointer_[7] = (source & 0x01) ? 0xff : 0x00;
pixel_pointer_ += 8;
pixels_ += 8;