forked from Apple-2-HW/arduino-appleii
42 lines
1.3 KiB
C++
42 lines
1.3 KiB
C++
// squash all the modes for this demo
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unsigned char appleToGhettoVGA(unsigned char apple) {
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if(apple >= 0xC0) return apple-0x40;
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else return apple&0x7F;
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}
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// Squash into normal mode
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unsigned char ghettoVGAToApple(unsigned char ghettoVga) {
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if(ghettoVga >= 0x40 && ghettoVga <= 0x7f) return ghettoVga;
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else return ghettoVga|0x80;
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}
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// Extract row, column addressing from woz's interlacing mode
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static unsigned char g_row = 0, g_col = 0;
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void decodeScreenAddress(unsigned short address) {
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unsigned char block_of_lines = (address>>7) - 0x08;
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unsigned char block_offset = (address&0x00FF) - ((block_of_lines&0x01) ? 0x80 : 0x00);
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if(block_offset < 0x28) {
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g_row = block_of_lines;
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g_col = block_offset;
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} else if(block_offset < 0x50) {
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g_row = block_of_lines + 8;
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g_col = block_offset-0x28;
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} else {
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g_row = block_of_lines + 16;
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g_col = block_offset-0x50;
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}
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}
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unsigned char screenRead(unsigned short address) {
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//Find our row/column
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decodeScreenAddress(address);
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return ghettoVGAToApple(readCharacter(g_row, g_col));
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}
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void screenWrite(unsigned short address, unsigned char value) {
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//Find our row/column
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decodeScreenAddress(address);
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// If not bell character
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if(value != 0x87) writeCharacter(g_row, g_col, appleToGhettoVGA(value));
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}
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