emul/hw/rc2014: implement blk write in sdc

All of that should help me implement sdc support much faster in
Forth.

emul/hw/rc2014/sdc.c

@@ -20,6 +20,7 @@ void sdc_init(SDC *sdc)
     sdc->resp = 0xff;
     sdc->fp = NULL;
     sdc->cmd17bytes = -1;
+    sdc->cmd24bytes = -2;
 }
 
 void sdc_cslow(SDC *sdc)
@@ -64,6 +65,47 @@ void sdc_spi_wr(SDC *sdc, uint8_t val)
         }
         return;
     }
+    if (sdc->cmd24bytes == -1) {
+        if (val == 0xff) {
+            // it's ok to receive idle bytes before the data token.
+            return;
+        }
+        if (val == 0xfe) {
+            // data token, good
+            sdc->cmd24bytes = 0;
+        } else {
+            // something is wrong, cancel cmd24
+            sdc->cmd24bytes = -2;
+        }
+        return;
+    }
+    if (sdc->cmd24bytes >= 0) {
+        if (sdc->cmd24bytes < 512) {
+            if (sdc->fp) {
+                putc(val, sdc->fp);
+            }
+            sdc->crc16 = crc16(sdc->crc16, val);
+        } else if (sdc->cmd24bytes == 512) {
+            // CRC MSB
+            if (val == (sdc->crc16>>8)) {
+                fprintf(stderr, "Good CRC16 MSB\n");
+            } else {
+                fprintf(stderr, "Bad CRC16 MSB\n");
+            }
+        } else {
+            if (val == (sdc->crc16&0xff)) {
+                fprintf(stderr, "Good CRC16 LSB\n");
+            } else {
+                fprintf(stderr, "Bad CRC16 LSB\n");
+            }
+            // valid response for CMD24
+            sdc->sendbuf[4] = 0x05;
+            sdc->sendidx = 4;
+            sdc->cmd24bytes = -3;
+        }
+        sdc->cmd24bytes++;
+        return;
+    }
     if ((sdc->recvidx == 0) && ((val > 0x7f) || (val < 0x40))) {
         // not a command
         return;
@@ -139,6 +181,17 @@ void sdc_spi_wr(SDC *sdc, uint8_t val)
         sdc->crc16 = 0;
         return;
     }
+    if (cmd == 24) {
+        fprintf(stderr, "cmd24\n");
+        if (sdc->fp) {
+            fseek(sdc->fp, arg2*512, SEEK_SET);
+        }
+        sdc->sendbuf[4] = 0x00;
+        sdc->sendidx = 4;
+        sdc->cmd24bytes = -1;
+        sdc->crc16 = 0;
+        return;
+    }
     // Simulate success for any unknown command.
     sdc->sendbuf[4] = 0x00;
     sdc->sendidx = 4;

emul/hw/rc2014/sdc.h

@@ -23,6 +23,9 @@ typedef struct {
     FILE *fp;
     // number of bytes read into the current CMD17. -1 means no CMD17 active.
     int cmd17bytes;
+    // number of bytes received for the current CMD24. -2 means no CMD24 active.
+    // -1 means we're still waiting for the data token.
+    int cmd24bytes;
     // running crc16 during read and write operations.
     uint16_t crc16;
 } SDC;