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https://github.com/mauiaaron/apple2.git
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Refactor various codepaths for clarity #2
This commit is contained in:
Aaron Culliney
parent
7a0255ff8b
commit
a5854a20f6
215
src/disk.c
215
src/disk.c
@ -74,10 +74,8 @@ static uint8_t rev_translate_table_6[0x80] = { 0 };
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__attribute__((constructor(CTOR_PRIORITY_LATE)))
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static void _initialize_reverse_translate(void) {
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unsigned int loop = 0;
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while (loop < 0x40) {
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rev_translate_table_6[translate_table_6[loop]-0x80] = loop << 2;
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loop++;
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for (unsigned int i=0; i<0x40; i++) {
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rev_translate_table_6[translate_table_6[i]-0x80] = i << 2;
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}
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}
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@ -120,73 +118,54 @@ static bool is_po(const char * const name) {
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#define NUM_SIXBIT_NIBS 342
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static void nibblize_sector(const uint8_t *src, uint8_t *out) {
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static void nibblize_sector(const uint8_t * const src, uint8_t *out) {
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SCOPE_TRACE_DISK("nibblize_sector");
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uint8_t work_buf[NUM_SIXBIT_NIBS];
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uint8_t work_buf[NUM_SIXBIT_NIBS+1];
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uint8_t *nib = work_buf;
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// Convert 256 8-bit bytes into 342 6-bit bytes
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{
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unsigned int counter = 0;
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uint8_t offset = 0xAC;
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while (offset != 0x02) {
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uint8_t value = (( (*(src+offset)) & 0x01) << 1) | (( (*(src+offset)) & 0x02) >> 1);
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offset -= 0x56;
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value = (value << 2) | (( (*(src+offset)) & 0x01) << 1) | (( (*(src+offset)) & 0x02) >> 1);
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offset -= 0x56;
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value = (value << 2) | (( (*(src+offset)) & 0x01) << 1) | (( (*(src+offset)) & 0x02) >> 1);
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offset -= 0x53;
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*(nib++) = value << 2;
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++counter;
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}
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*(nib-2) &= 0x3F;
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*(nib-1) &= 0x3F;
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assert((counter == NUM_SIXBIT_NIBS-0x100) && "nibblizing counter about to overflow");
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memcpy(nib, src, 0x100);
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unsigned int counter = 0;
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uint8_t offset = 0xAC;
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while (offset != 0x02) {
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uint8_t value = (( (*(src+offset)) & 0x01) << 1) | (( (*(src+offset)) & 0x02) >> 1);
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offset -= 0x56;
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value = (value << 2) | (( (*(src+offset)) & 0x01) << 1) | (( (*(src+offset)) & 0x02) >> 1);
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offset -= 0x56;
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value = (value << 2) | (( (*(src+offset)) & 0x01) << 1) | (( (*(src+offset)) & 0x02) >> 1);
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offset -= 0x53;
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*(nib++) = value << 2;
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++counter;
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}
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src = work_buf;
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uint8_t work_buf2[NUM_SIXBIT_NIBS+1];
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nib = work_buf2;
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*(nib-2) &= 0x3F;
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*(nib-1) &= 0x3F;
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assert((counter == NUM_SIXBIT_NIBS-0x100) && "nibblizing counter about to overflow");
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memcpy(nib, src, 0x100);
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// XOR the entire data block with itself offset by one byte, creating a final checksum byte
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{
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uint8_t savedval = 0;
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int loop = NUM_SIXBIT_NIBS;
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while (loop--) {
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*(nib++) = savedval ^ *src;
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savedval = *(src++);
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}
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*nib = savedval;
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uint8_t savedval = 0;
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for (unsigned int i=0; i<NUM_SIXBIT_NIBS; i++) {
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uint8_t prevsaved = savedval ^ work_buf[i];
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savedval = work_buf[i];
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work_buf[i] = prevsaved;
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}
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src = work_buf2;
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nib = NULL;
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work_buf[NUM_SIXBIT_NIBS] = savedval;
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// Convert the 6-bit bytes into disk bytes using a lookup table. A valid disk byte is a byte that has the high bit
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// set, at least two adjacent bits set (excluding the high bit), and at most one pair of consecutive zero bits.
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{
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int loop = NUM_SIXBIT_NIBS+1;
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while (loop--) {
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*(out++) = translate_table_6[(*(src++)) >> 2];
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}
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for (unsigned int i=0; i<NUM_SIXBIT_NIBS+1; i++) {
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*(out++) = translate_table_6[work_buf[i] >> 2];
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}
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}
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static void denibblize_sector(const uint8_t *src, uint8_t *out) {
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static void denibblize_sector(const uint8_t * const src, uint8_t *out) {
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SCOPE_TRACE_DISK("denibblize_sector");
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uint8_t work_buf[NUM_SIXBIT_NIBS+1];
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uint8_t *dsk = work_buf;
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// Convert disk bytes into 6-bit bytes
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{
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unsigned int loop = NUM_SIXBIT_NIBS+1;
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while (loop--) {
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*(dsk++) = rev_translate_table_6[*(src++) & 0x7F];
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}
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for (unsigned int i=0; i<(NUM_SIXBIT_NIBS+1); i++) {
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work_buf[i] = rev_translate_table_6[src[i] & 0x7F];
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}
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#if DISK_TRACING
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@ -199,56 +178,47 @@ static void denibblize_sector(const uint8_t *src, uint8_t *out) {
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}
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#endif
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src = work_buf;
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uint8_t work_buf2[NUM_SIXBIT_NIBS];
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dsk = work_buf2;
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// XOR the entire data block with itself offset by one byte to undo checksumming
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{
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uint8_t savedval = 0;
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unsigned int loop = NUM_SIXBIT_NIBS;
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while (loop--) {
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*dsk = savedval ^ *(src++);
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savedval = *(dsk++);
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}
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uint8_t savedval = 0;
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for (unsigned int i=0; i<NUM_SIXBIT_NIBS; i++) {
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work_buf[i] = savedval ^ work_buf[i];
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savedval = work_buf[i];
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}
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#if DISK_TRACING
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if (test_write_fp) {
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fprintf(test_write_fp, "XORNIBS:\n");
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for (unsigned int i=0; i<NUM_SIXBIT_NIBS; i++) {
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fprintf(test_write_fp, "%02X", work_buf2[i]);
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fprintf(test_write_fp, "%02X", work_buf[i]);
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}
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fprintf(test_write_fp, "\n");
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}
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#endif
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// Convert 342 6-bit bytes into 256 8-bit bytes
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{
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uint8_t *lowbitsptr = work_buf2;
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uint8_t *sectorbase = work_buf2+0x56;
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uint8_t offset = 0xAC;
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unsigned int counter = 0;
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while (offset != 0x02) {
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assert(counter < 256 && "denibblizing counter overflow");
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if (offset >= 0xAC) {
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*(out+offset) = (*(sectorbase+offset) & 0xFC) | (((*lowbitsptr) & 0x80) >> 7) | (((*lowbitsptr) & 0x40) >> 5);
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++counter;
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}
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offset -= 0x56;
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*(out+offset) = (*(sectorbase+offset) & 0xFC) | (((*lowbitsptr) & 0x20) >> 5) | (((*lowbitsptr) & 0x10) >> 3);
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uint8_t *lowbitsptr = work_buf;
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uint8_t *sectorbase = work_buf+0x56;
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uint8_t offset = 0xAC;
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unsigned int counter = 0;
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while (offset != 0x02) {
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assert(counter < 256 && "denibblizing counter overflow");
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if (offset >= 0xAC) {
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*(out+offset) = (*(sectorbase+offset) & 0xFC) | (((*lowbitsptr) & 0x80) >> 7) | (((*lowbitsptr) & 0x40) >> 5);
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++counter;
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offset -= 0x56;
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*(out+offset) = (*(sectorbase+offset) & 0xFC) | (((*lowbitsptr) & 0x08) >> 3) | (((*lowbitsptr) & 0x04) >> 1);
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++counter;
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offset -= 0x53;
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++lowbitsptr;
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}
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assert(counter == 256 && "invalid bytes count");
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offset -= 0x56;
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*(out+offset) = (*(sectorbase+offset) & 0xFC) | (((*lowbitsptr) & 0x20) >> 5) | (((*lowbitsptr) & 0x10) >> 3);
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++counter;
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offset -= 0x56;
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*(out+offset) = (*(sectorbase+offset) & 0xFC) | (((*lowbitsptr) & 0x08) >> 3) | (((*lowbitsptr) & 0x04) >> 1);
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++counter;
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offset -= 0x53;
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++lowbitsptr;
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}
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assert(counter == 256 && "invalid bytes count");
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#ifdef DISK_TRACING
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if (test_write_fp) {
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@ -370,47 +340,60 @@ static void denibblize_track(int drive, uint8_t *dst) {
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unsigned int offset = 0;
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int sector = -1;
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// iterate over 2x sector count (header and data sections)
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// iterate over 2x sectors (accounting for header and data sections)
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for (unsigned int sct2=0; sct2<(NUM_SECTORS<<1)+1; sct2++) {
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uint8_t prologue[3] = {0,0,0}; // D5AA..
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// Find a prologue
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unsigned int count = 0;
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unsigned int loop = NIB_TRACK_SIZE;
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while (loop && (count < 3)) {
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--loop;
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if (count || (*(trackimage+offset) == 0xD5)) {
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prologue[count] = *(trackimage+offset);
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++count;
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// Find the beginning of a header or data prologue
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for (unsigned int i=0, idx=0; i<NIB_TRACK_SIZE; i++) { // FIXME: probably can change this to NIB_SEC_SIZE*2 ...
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uint8_t byte = trackimage[offset];
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if (idx || (byte == 0xD5)) {
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prologue[idx] = byte;
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++idx;
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}
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++offset;
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if (offset >= disk6.disk[drive].track_width) {
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offset = 0;
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}
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}
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if ((count == 3) && (prologue[1] == 0xAA)) {
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#define DATA_BYTES_LEN (256+128)
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#define SCTOFF_HI 0x4
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#define SCTOFF_LO 0x5
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unsigned int tmpoff = offset;
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uint8_t work_buf[DATA_BYTES_LEN] = { 0 };
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for (unsigned int i=0; i<DATA_BYTES_LEN; i++) {
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work_buf[i] = *(trackimage+tmpoff);
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++tmpoff;
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if (tmpoff >= disk6.disk[drive].track_width) {
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tmpoff = 0;
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}
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}
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if (prologue[2] == 0x96) { // header
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sector = ((work_buf[SCTOFF_HI] & 0x55) << 1) | (work_buf[SCTOFF_LO] & 0x55);
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} else if (prologue[2] == 0xAD) { // data
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int sec_off = 256 * disk6.disk[drive].skew_table[ sector ];
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denibblize_sector(work_buf, dst+sec_off);
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sector = -1;
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if (idx >= 3) {
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break;
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}
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}
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if (prologue[1] != 0xAA) {
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continue;
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}
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#define SCTOFF 0x4
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if (prologue[2] == 0x96) {
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// found header prologue : extract sector
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offset += SCTOFF;
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if (offset >= disk6.disk[drive].track_width) {
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RELEASE_LOG("WRAPPING PROLOGUE ...");
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offset -= disk6.disk[drive].track_width;
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}
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sector = ((trackimage[offset++] & 0x55) << 1);
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sector |= (trackimage[offset++] & 0x55);
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continue;
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}
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if (UNLIKELY(prologue[2] != 0xAD)) {
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RELEASE_LOG("OMG, found mid-track 0xD5 byte...");
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continue;
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}
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// found data prologue : copy and write data to sector
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uint8_t work_buf[NUM_SIXBIT_NIBS+1];
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for (unsigned int idx=0; idx<(NUM_SIXBIT_NIBS+1); idx++) {
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work_buf[idx] = trackimage[offset];
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++offset;
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if (offset >= disk6.disk[drive].track_width) {
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offset = 0;
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}
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}
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int sec_off = 256 * disk6.disk[drive].skew_table[ sector ];
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denibblize_sector(work_buf, dst+sec_off);
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sector = -1;
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}
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}
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