247 lines
7.6 KiB
Java
247 lines
7.6 KiB
Java
package com.bytezone.diskbrowser.applefile;
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import com.bytezone.diskbrowser.utilities.CPU;
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// -----------------------------------------------------------------------------------//
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public class DoubleScrunchCPU extends CPU
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// -----------------------------------------------------------------------------------//
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{
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private byte mem_71D0; // varies 1/0/1/0 ...
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private byte mem_71D2; // column index * 2 (00-4F) increments every C0 bytes
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private byte mem_71D3; // byte to repeat
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private byte mem_71D4; // repetition counter
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private int src; // base address of packed buffer
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private int dst; // base address of main/aux memory
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private byte zp_00; // input buffer offset
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private byte zp_01;
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private byte zp_26; // output buffer offset
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private byte zp_27;
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private byte zp_E6; // hi-res page ($20 or $40)
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final byte[][] memory = new byte[2][0x2000];
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private byte[] packedBuffer;
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private int count;
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// ---------------------------------------------------------------------------------//
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void unscrunch (byte[] buffer)
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// ---------------------------------------------------------------------------------//
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{
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packedBuffer = buffer;
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src = 0x4000; // packed picture data
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dst = 0x2000; // main/aux picture data
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zp_00 = 0x00; // load address of packed buffer
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zp_01 = 0x40;
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zp_E6 = 0x20; // hi-res page 1
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lda (zp_E6);
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ora ((byte) 0x04);
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zp_27 = sta ();
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ldx ((byte) 0x01);
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mem_71D0 = stx (); // X and 71D0 are both set to 1
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ldy ((byte) 0x00);
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mem_71D2 = sty (); // column index = 0
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zp_26 = sty (); // output index = 0
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while (true)
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{
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// get the repetition counter (hi-bit is a flag to indicate copy/repeat)
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lda (packedBuffer, indirectY (src, zp_00, zp_01)); // LDA ($00),Y)
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php ();
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// increment address to get next transfer byte (done in copy/repeat routine)
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zp_00 = inc (zp_00);
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if (zero)
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zp_01 = inc (zp_01);
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and ((byte) 0x7F); // remove copy/repeat flag
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mem_71D4 = sta (); // save repetition counter (RC)
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plp ();
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// copy or repeat RC bytes
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if (negative ? copyBytes () : repeatBytes ())
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break;
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// increment address to get next repetition counter
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zp_00 = inc (zp_00);
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if (zero)
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zp_01 = inc (zp_01);
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}
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}
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// copy a single byte RC times
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// ---------------------------------------------------------------------------------//
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private boolean repeatBytes ()
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// ---------------------------------------------------------------------------------//
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{
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// get the byte to store
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lda (packedBuffer, indirectY (src, zp_00, zp_01)); // LDA ($00),Y)
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mem_71D3 = sta ();
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while (true)
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{
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lda (mem_71D3); // get the byte to store
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storeByte (); // store it and decrement repetition counter
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calculateScreenColumn ();
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if (carry)
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return true; // completely finished
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calculateNextScreenAddress ();
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ldy (mem_71D4); // check the repetition counter
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if (zero)
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return false; // not finished
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}
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}
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// copy the next RC bytes
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// ---------------------------------------------------------------------------------//
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private boolean copyBytes ()
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// ---------------------------------------------------------------------------------//
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{
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while (true)
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{
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// get the byte to store
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ldy ((byte) 0x00);
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lda (packedBuffer, indirectY (src, zp_00, zp_01)); // LDA ($00),Y)
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storeByte (); // store it and decrement repetition counter
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calculateScreenColumn ();
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if (carry)
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return true; // completely finished
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calculateNextScreenAddress ();
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ldy (mem_71D4); // check the repetition counter
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if (zero)
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return false; // not finished
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// prepare address for next read
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zp_00 = inc (zp_00);
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if (zero)
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zp_01 = inc (zp_01);
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}
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}
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// store the byte currently in Acc
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// ---------------------------------------------------------------------------------//
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private void storeByte ()
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// ---------------------------------------------------------------------------------//
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{
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mem_71D4 = dec (mem_71D4); // decrement repetition counter (RC)
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ldy (mem_71D2); // column index (times 2)
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php ();
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// sei ();
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pha ();
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tya ();
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lsr (); // divide by 2, put odd/even value in carry (bank)
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tay ();
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pla ();
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if (false)
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System.out.printf (
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"%04X D0: %02X D2: %02X xReg: %02X bank: %d %02X -> %02X %02X + %02X%n",
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count++, mem_71D0, mem_71D2, stx (), carry ? 0 : 1, sta (), zp_27, zp_26,
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sty ());
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// store byte
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sta (memory[carry ? 1 : 0], indirectY (dst, zp_26, zp_27));
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plp ();
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}
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// $71B1
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// ---------------------------------------------------------------------------------//
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private void calculateScreenColumn ()
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// ---------------------------------------------------------------------------------//
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{
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// increment X by 2 - X varies 01, 03, 05 -> BF, then 00, 02, 04 -> BE
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inx ();
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inx ();
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cpx ((byte) 0xC0); // # screen lines
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if (!carry) // X < $C0
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return; // continue current phase
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// carry is now set, current phase is finished
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// change phase
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mem_71D0 = dec (mem_71D0); // either 1 -> 0, or 0 -> -1
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if (!negative) //
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{
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assert mem_71D0 == 0;
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// start second phase of screen column
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ldx ((byte) 0x00); // start X at 0
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// mem_71D0 = stx (); // phase 2 (not necessary, was already 0)
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clc ();
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return; // start phase 2
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}
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// start a new screen column (and start phase 1)
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mem_71D2 = inc (mem_71D2); // increment column index
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ldy (mem_71D2);
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cpy ((byte) 0x50); // test for end of line (2 x 0x28)
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if (carry) // Y >= $50
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return; // program finished
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ldx ((byte) 0x01); // start X at 1
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mem_71D0 = stx (); // start phase 1
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clc ();
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}
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// set locations $26-27 (address of first location in screen line)
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// ---------------------------------------------------------------------------------//
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private void calculateNextScreenAddress ()
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// ---------------------------------------------------------------------------------//
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{
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txa ();
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and ((byte) 0xC0); // get 2 hi bits - 00/40/80
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zp_26 = sta ();
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lsr ();
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lsr ();
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ora (zp_26); // graphics page ($20 or $40)
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zp_26 = sta ();
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txa ();
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zp_27 = sta ();
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asl ();
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asl ();
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asl ();
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zp_27 = rol (zp_27);
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asl ();
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zp_27 = rol (zp_27);
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asl ();
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zp_26 = ror (zp_26);
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lda (zp_27);
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and ((byte) 0x1F); // clear bits 7-5
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ora (zp_E6); // graphics page ($20 or $40)
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zp_27 = sta ();
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}
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// ---------------------------------------------------------------------------------//
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@Override
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protected String debugString ()
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// ---------------------------------------------------------------------------------//
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{
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return String.format ("0: %02X %02X 26: %02X %02X %02X %02X %02X %02X", zp_00,
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zp_01, zp_26, zp_27, mem_71D0, mem_71D2, mem_71D3, mem_71D4);
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}
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}
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