fmtx: be smarter about speed changes

USBCAS/fmtx.c

@@ -46,13 +46,16 @@ ISR(USART1_UDRE_vect)
 	static struct cas_block *blk = &block[0];
 	uint8_t pattern;
 
-	if (!tx_bits) {
+	while (!tx_bits) {
 		if (!blk->ready || !motor_relay()) {
 			/* Hold the line for one pattern time, then idle */
 			UCSR1A = TX_IDLE;
 			UDR1   = parity;
 			fmtx_disable(); /* Nothing left to do */
 			return;
+		} 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++];
 			tx_bits = 8;
@@ -63,14 +66,9 @@ ISR(USART1_UDRE_vect)
 			blk->pause--;
 			return;
 		} else {
-			if (blk->data.blktype == 0xff &&
-			    blk->data.hdr.divisor) {
-				fmtx_set_speed(blk->data.hdr.divisor);
-			}
-			blk->ready = false; /* Free to use */
+			blk->ready = false; /* Free buffer */
 			blk = blk->next;
 			tx_offset = 0;
-			return;	/* Will probably re-trigger immediately */
 		}
 	}
 
@@ -186,18 +184,21 @@ bool fmtx_full(void)
 	return rx_blk->ready;
 }
 
-static enum rx_state setup_block(unsigned int divisor, unsigned int blkno)
+static void fmtx_wait_for_free_buffer(void)
 {
-	uint8_t blktype;
+	while (rx_blk->ready)
+		do_usb_tasks();
+}
 
-	fmtx_drain();
-	fmtx_set_speed(divisor);
+static enum rx_state setup_block(unsigned int blkno)
+{
+	uint8_t blktype;
 
 	rx_blk->data.blkno = blkno;
 	blktype = -(blkno == -1U);
 	rx_blk->data.blktype = blktype;
 
-	rx_blk->pause = block_pause(blktype, divisor);
+	rx_blk->pause = block_pause(blktype, rx_blk->divisor);
 
 	/* Initialize checksum */
 	rx_blk->data.csum = 0x03  /* ETX is part of the checksum */
@@ -230,28 +231,38 @@ static enum rx_state do_cmd(uint8_t cmd, const uint16_t *arg)
 	case 'R':
 		/* Set receive baudrate divisor */
 		/* &R divisor */
-		fmrx_set_speed(arg[0]);
+		fmtx_wait_for_free_buffer();
+		rx_blk->divisor = arg[0];
 		return rx_idle;
 
 	case 'H':
 		/* Send header block */
-		/* &H divisor */
+		/* &H */
 		rx_blk_cnt = 1;
-		return setup_block(arg[0], -1);
+		return setup_block(-1);
 
 	case 'D':
 		/* Send data block */
-		/* &D divisor,blocknr */
+		/* &D blocknr */
 		rx_blk_cnt = 1;
-		return setup_block(arg[0], arg[1]);
+		return setup_block(arg[0]);
 
 	case 'F':
+	{
+		uint8_t divisor;
+
 		/* Send file */
 		/* &F filename,blocks[,divisor] */
+		setup_block(-1);
+
 		rx_blk_cnt = arg[0];
-		setup_block(arg[1], -1);
-		rx_blk->data.hdr.divisor =
-			(arg[1] == CAS_DIVISOR_ABC80) ? 0 : arg[1];
+		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;
 
@@ -262,7 +273,17 @@ static enum rx_state do_cmd(uint8_t cmd, const uint16_t *arg)
 
 		rx_blk->ready = true;
 		rx_blk = rx_blk->next;
-		return rx_blk_cnt ? rx_data : rx_idle;
+
+		if (!rx_blk_cnt)
+			return rx_idle;
+
+		if (divisor) {
+			fmtx_wait_for_free_buffer();
+			rx_blk->divisor = divisor;
+		}
+
+		return rx_data;
+	}
 
 	default:
 		return rx_idle;	/* Unknown/unimplemented command */
@@ -280,6 +301,7 @@ void fmtx_recv_byte(uint8_t byte)
 		if (byte == '&')
 			rx_state = rx_cmd;
 		break;
+
 	case rx_cmd:
 		ctr = 0;
 		memset(arg, 0, sizeof arg);
@@ -293,6 +315,7 @@ void fmtx_recv_byte(uint8_t byte)
 		else
 			rx_state = rx_idle;
 		break;
+
 	case rx_filename:
 		switch (byte) {
 		case '\n':
@@ -318,6 +341,7 @@ void fmtx_recv_byte(uint8_t byte)
 			break;
 		}
 		break;
+
 	case rx_num:
 		if (byte == '\n') {
 			ctr = 0;
@@ -331,16 +355,21 @@ void fmtx_recv_byte(uint8_t byte)
 				arg[ctr] = arg[ctr]*10 + byte;
 		}
 		break;
+
 	case rx_data:
 		rx_blk->data.data[ctr++] = byte;
 		rx_blk->data.csum += byte;
-		if (ctr == 253) {
+		if (ctr >= 253) {
+			uint16_t nextblk = rx_blk->data.blkno + 1;
 			rx_blk->ready = true;
 			rx_blk = rx_blk->next;
-			if (!--rx_blk_cnt) {
+			fmtx_enable();
+			if (--rx_blk_cnt) {
+				fmtx_wait_for_free_buffer();
+				setup_block(nextblk);
+			} else {
 				rx_state = rx_idle;
 			}
-			fmtx_enable();
 		}
 		break;
 	}

USBCAS/usbcas.h

@@ -76,6 +76,7 @@ struct cas_block_data {
 /* Cassette block plus metadata */
 struct cas_block {
 	volatile bool ready;	/* Filled with data */
+	uint8_t divisor;	/* Transmission divisor (0 = unchanged) */
 	unsigned int pause;	/* Post-block delay */
 	struct cas_block *next;	/* Next block pointer */
 	struct cas_block_data data;