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https://github.com/mauiaaron/apple2.git
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Refactor various codepaths for clarity #3
This commit is contained in:
Aaron Culliney
parent
a5854a20f6
commit
ce7596754b
132
src/disk.c
132
src/disk.c
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@ -116,31 +116,65 @@ static bool is_po(const char * const name) {
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return false;
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}
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#define NUM_SIXBIT_NIBS 342
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#define SIXBIT_MASK 0x3F // 111111
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#define SIXBIT_EXTRA_BYTES 0x56 // 86
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#define SIXBIT_EXTRA_WRAP 0x53 // 86 + 86 + 83 == 255
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#define SIXBIT_OFF_BEGIN (SIXBIT_EXTRA_BYTES<<1) // 0xAC
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#define NUM_SIXBIT_NIBS (0x100 + SIXBIT_EXTRA_BYTES) // 256 + 86 == 342
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static void nibblize_sector(const uint8_t * const src, uint8_t *out) {
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#if DISK_TRACING
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#define _DISK_TRACE_SIXBITNIBS() \
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if (test_write_fp) { \
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fprintf(test_write_fp, "SIXBITNIBS:\n"); \
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for (unsigned int i=0; i<NUM_SIXBIT_NIBS+1; 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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#define _DISK_TRACE_XORNIBS() \
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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_buf[i]); \
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} \
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fprintf(test_write_fp, "\n"); \
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}
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#define _DISK_TRACE_SECDATA() \
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if (test_write_fp) { \
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fprintf(test_write_fp, "SECTOR:\n"); \
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for (unsigned int i = 0; i < 256; i++) { \
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fprintf(test_write_fp, "%02X", out[i]); \
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} \
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fprintf(test_write_fp, "%s", "\n"); \
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}
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#else
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#define _DISK_TRACE_SIXBITNIBS()
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#define _DISK_TRACE_XORNIBS()
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#define _DISK_TRACE_SECDATA()
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#endif
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static void nibblize_sector(const uint8_t * const src, uint8_t * const out) {
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SCOPE_TRACE_DISK("nibblize_sector");
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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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unsigned int counter = 0;
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uint8_t offset = 0xAC;
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uint8_t offset = SIXBIT_OFF_BEGIN;
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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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uint8_t value = ((src[offset] & 0x01) << 1) | ((src[offset] & 0x02) >> 1);
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offset -= SIXBIT_EXTRA_BYTES;
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value = (value << 2) | ((src[offset] & 0x01) << 1) | ((src[offset] & 0x02) >> 1);
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offset -= SIXBIT_EXTRA_BYTES;
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value = (value << 2) | ((src[offset] & 0x01) << 1) | ((src[offset] & 0x02) >> 1);
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offset -= SIXBIT_EXTRA_WRAP;
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work_buf[counter] = 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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work_buf[counter-2] &= SIXBIT_MASK;
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work_buf[counter-1] &= SIXBIT_MASK;
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memcpy(&work_buf[counter], 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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uint8_t savedval = 0;
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@ -154,11 +188,11 @@ static void nibblize_sector(const uint8_t * const src, uint8_t *out) {
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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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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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out[i] = 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 * const src, uint8_t *out) {
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static void denibblize_sector(const uint8_t * const src, uint8_t * const 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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@ -167,16 +201,7 @@ static void denibblize_sector(const uint8_t * const src, uint8_t *out) {
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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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if (test_write_fp) {
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fprintf(test_write_fp, "SIXBITNIBS:\n");
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for (unsigned int i=0; i<NUM_SIXBIT_NIBS+1; 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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_DISK_TRACE_SIXBITNIBS();
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// XOR the entire data block with itself offset by one byte to undo checksumming
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uint8_t savedval = 0;
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@ -184,51 +209,30 @@ static void denibblize_sector(const uint8_t * const src, uint8_t *out) {
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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_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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_DISK_TRACE_XORNIBS();
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// Convert 342 6-bit bytes into 256 8-bit bytes
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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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uint8_t *sectorbase = work_buf+SIXBIT_EXTRA_BYTES;
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uint8_t offset = SIXBIT_OFF_BEGIN;
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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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for (unsigned int i=0; i<SIXBIT_EXTRA_BYTES; i++) {
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if (offset >= SIXBIT_OFF_BEGIN) {
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out[offset] = (sectorbase[offset] & 0xFC) | ((lowbitsptr[i] & 0x80) >> 7) | ((lowbitsptr[i] & 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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offset -= SIXBIT_EXTRA_BYTES;
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out[offset] = (sectorbase[offset] & 0xFC) | ((lowbitsptr[i] & 0x20) >> 5) | ((lowbitsptr[i] & 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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offset -= SIXBIT_EXTRA_BYTES;
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out[offset] = (sectorbase[offset] & 0xFC) | ((lowbitsptr[i] & 0x08) >> 3) | ((lowbitsptr[i] & 0x04) >> 1);
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++counter;
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offset -= 0x53;
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++lowbitsptr;
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offset -= SIXBIT_EXTRA_WRAP;
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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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fprintf(test_write_fp, "SECTOR:\n");
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for (unsigned int i = 0; i < 256; i++) {
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fprintf(test_write_fp, "%02X", out[i]);
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}
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fprintf(test_write_fp, "%s", "\n");
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}
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#endif
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assert(counter == 0x100 && "invalid bytes count");
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assert(offset == 2 && "invalid bytes count");
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_DISK_TRACE_SECDATA();
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}
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#define CODE44A(a) ((((a)>> 1) & 0x55) | 0xAA)
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@ -238,7 +242,7 @@ static unsigned long nibblize_track(uint8_t *buf, int drive) {
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SCOPE_TRACE_DISK("nibblize_track");
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uint8_t *output = disk6.disk[drive].track_image;
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#if CONFORMANT_TRACKS
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// Write track-beginning gap containing 48 self-sync bytes
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for (unsigned int i=0; i<48; i++) {
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@ -324,7 +328,7 @@ static unsigned long nibblize_track(uint8_t *buf, int drive) {
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return output-disk6.disk[drive].track_image;
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}
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static void denibblize_track(int drive, uint8_t *dst) {
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static void denibblize_track(int drive, uint8_t * const dst) {
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SCOPE_TRACE_DISK("denibblize_track");
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// Searches through the track data for each sector and decodes it
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