fmtx: add &P command to explicitly insert a pause

Add a command to explicitly generate an interblock space, if needed.

USBCAS/fmtx.c

@@ -42,7 +42,6 @@ static uint8_t parity;
 ISR(USART1_UDRE_vect)
 {
 	static uint8_t tx_data, tx_bits;
-	static unsigned int tx_offset; /* Offset into current buffer */
 	static struct cas_block *blk = &block[0];
 	uint8_t pattern;
 
@@ -56,8 +55,9 @@ ISR(USART1_UDRE_vect)
 		} else if (blk->divisor) {
 			fmtx_set_speed(blk->divisor);
 			blk->divisor = 0;
-		} else if (tx_offset < sizeof blk->data) {
-			tx_data = ((const uint8_t *)&blk->data)[tx_offset++];
+			return;
+		} else if (blk->offset < sizeof blk->data) {
+			tx_data = ((const uint8_t *)&blk->data)[blk->offset++];
 			tx_bits = 8;
 		} else if (blk->pause) {
 			/* Interblock silence; hold the line */
@@ -68,7 +68,6 @@ ISR(USART1_UDRE_vect)
 		} else {
 			blk->ready = false; /* Free buffer */
 			blk = blk->next;
-			tx_offset = 0;
 		}
 	}
 
@@ -204,6 +203,9 @@ static enum rx_state setup_block(unsigned int blkno)
 	rx_blk->data.csum = 0x03  /* ETX is part of the checksum */
 		+ blktype + (uint8_t)blkno + (uint8_t)(blkno >> 8);
 
+	/* Start at beginning of data */
+	rx_blk->offset = 0;
+
 	return rx_data;
 }
 
@@ -249,19 +251,18 @@ static enum rx_state do_cmd(uint8_t cmd, const uint16_t *arg)
 
 	case 'F':
 	{
-		uint8_t divisor;
-
 		/* Send file */
 		/* &F filename,blocks[,divisor] */
+
+		uint8_t divisor = arg[1];
+		if (divisor == CAS_DIVISOR_ABC80)
+			divisor = 0;
+
 		setup_block(-1);
 
 		rx_blk_cnt = arg[0];
 		rx_blk->divisor = CAS_DIVISOR_ABC80; /* Header always slow */
 
-		divisor = arg[1];
-		if (divisor == CAS_DIVISOR_ABC80)
-			divisor = 0;
-
 		rx_blk->data.hdr.divisor = divisor;
 		memset(rx_blk->data.hdr.zero, 0, sizeof rx_blk->data.hdr.zero);
 		rx_blk->data.hdr.nblocks = rx_blk_cnt;
@@ -285,6 +286,17 @@ static enum rx_state do_cmd(uint8_t cmd, const uint16_t *arg)
 		return rx_data;
 	}
 
+	case 'P':
+		/* Pause (produce silence) */
+		/* &P byte_times */
+		if (arg[0]) {
+			fmtx_wait_for_free_buffer();
+			rx_blk->pause = arg[0] << BIT_PATTERN_LEN_LG2;
+			rx_blk->offset = sizeof rx_blk->data; /* No data */
+			rx_blk->ready = true;
+		}
+		return rx_idle;
+
 	default:
 		return rx_idle;	/* Unknown/unimplemented command */
 	}

USBCAS/usbcas.h

@@ -78,6 +78,7 @@ struct cas_block {
 	volatile bool ready;	/* Filled with data */
 	uint8_t divisor;	/* Transmission divisor (0 = unchanged) */
 	unsigned int pause;	/* Post-block delay */
+	unsigned int offset;	/* Offset into data buffer */
 	struct cas_block *next;	/* Next block pointer */
 	struct cas_block_data data;
 };