fmtx: do allow the output to go high when not in use

Do allow the output to go high when end of data is reached.

USBCAS/fmrx.c

@@ -98,7 +98,7 @@ void fmrx_set_speed(uint32_t baudrate)
 #define CAS_BLOCK_LEN    (1+2+253+1+2) /* type+num+data+ETX+checksum */
 
 /* Finish a bit due to clock edge or timeout */
-static void finish_bit(void)
+static inline ATTR_ALWAYS_INLINE void finish_bit(void)
 {
 	if (!started)
 		return;

USBCAS/fmtx.c

@@ -10,11 +10,16 @@
 
 #include "fmpat.h"
 
-static uint8_t parity = 0;
-static uint8_t tx_idle;
 #define TX_BUSY	0
 #define TX_IDLE (1 << TXC1)
 
+static inline ATTR_ALWAYS_INLINE void fmtx_disable(void)
+{
+	UCSR1B &= ~(1 << UDRIE1);
+}
+
+static uint8_t parity;
+
 /*
  * Send stuff if we have anything to send
  */
@@ -30,29 +35,27 @@ ISR(USART1_UDRE_vect)
 		if (nd < 0) {
 			/*
 			 * Nothing to send. Disable the interrupt and
-			 * send out an idle zero to make sure the output
-			 * is low when not used; otherwise the motor
-			 * detect won't work. Unfortunately we have to
-			 * keep doing so and can't simply disable the
-			 * interrupt routine.
+			 * send out one last edge. Afterwards, the hardware
+			 * will drive the line high.
 			 */
-			if (!tx_idle)
-				UCSR1A = tx_idle = TX_IDLE;
-			UDR1    = parity = 0;
+			fmtx_disable();
+
+			UCSR1A = TX_IDLE;
+			UDR1 = parity; /* One last edge before going high */
+			parity = 0;
 			return;
 		}
 		data = nd;
 		left = 8;
 	}
 
-	tx_idle = TX_BUSY;
-
-	pattern = fm_pat[data & PATTERN_BIT_MASK] ^ parity;
+	pattern = fm_pat[data & PATTERN_BIT_MASK] ^ ~parity;
 
+	UCSR1A = TX_IDLE;
 	UDR1 = pattern;
 	data >>= BITS_PER_PATTERN_BYTE;
 	left -= BITS_PER_PATTERN_BYTE;
-	parity = -((int8_t)pattern < 0);
+	parity = -((int8_t)pattern >= 0);
 }
 
 /*
@@ -61,7 +64,7 @@ ISR(USART1_UDRE_vect)
 void fmtx_drain(void)
 {
 	/* Wait until input queue is idle and we have had at least one output */
-	while (!(UCSR1A & tx_idle))
+	while ((UCSR1B & (1 << UDRIE1)) || !(UCSR1A & TX_IDLE))
 		do_usb_task();
 }
 
@@ -88,11 +91,13 @@ uint32_t fmtx_real_baudrate(uint32_t baudrate)
 
 void fmtx_init_speed(uint32_t baudrate)
 {
+	parity = 0;		/* We start out with a high idle */
+
 	UCSR1B = 0;		/* Disable transmitter and ISR */
 	UCSR1A = (1 << TXC1);	/* Clear TXC bit */
 
-	DDRD |= 0x28; /* PD3 = outdata, PD5 = XCK/TXLED */
-	PORTD = (PORTD & ~0x28) | 0x20;
+	DDRD  |= 0x28; /* PD3 = outdata, PD5 = XCK/TXLED */
+	PORTD |= 0x28; /* Drive data and clock high while idle */
 
 	/*
 	 * SPI master mode, mode 1, LSB first
@@ -114,5 +119,5 @@ void fmtx_init_speed(uint32_t baudrate)
 	 * Enable transmitter ISR (which probably will immediately
 	 * go to idle...)
 	 */
-	UCSR1B |= (1 << UDRIE1);
+	fmtx_enable();
 }

USBCAS/usbcas.c

@@ -41,9 +41,9 @@
 /*
  * Input and output ring buffers
  */
-static RingBuffer_t u2c_ringbuf;	/* USB -> CDC */
-static uint8_t      u2c_buffer[128];
-static RingBuffer_t c2u_ringbuf;	/* CDC -> USB */
+static RingBuffer_t u2c_ringbuf;	/* USB -> CAS */
+static uint8_t      u2c_buffer[512];
+static RingBuffer_t c2u_ringbuf;	/* CAS -> USB */
 static uint8_t      c2u_buffer[128];
 
 /**
@@ -143,10 +143,10 @@ ISR(TIMER3_CAPT_vect)
 static void update_modem_status(USB_ClassInfo_CDC_Device_t * const cii,
 				bool forced)
 {
-	uint16_t lines = CDC_CONTROL_LINE_IN_DSR;
+	uint16_t lines = 0;
 
 	if (motor_relay) /* Cassette relay active */
-		lines |= CDC_CONTROL_LINE_IN_DCD;
+		lines |= CDC_CONTROL_LINE_IN_DCD | CDC_CONTROL_LINE_IN_DSR;
 
 	if (forced || cii->State.ControlLineStates.DeviceToHost != lines) {
 		cii->State.ControlLineStates.DeviceToHost = lines;
@@ -186,6 +186,68 @@ static bool usb_send_next_byte(void)
 	return false;
 }
 
+static void usb_recv_data(void)
+{
+	int byte;
+
+	/*
+	 * Only try to read in bytes from the CDC interface if
+	 * the transmit buffer is not full
+	 */
+	if (RingBuffer_IsFull(&u2c_ringbuf))
+		return;
+
+	byte = CDC_Device_ReceiveByte(&vcpif);
+	if (byte < 0)
+		return;		/* No data */
+
+	/*
+	 * Store received byte into the transmit buffer, then
+	 * enable the transmit ISR if disabled
+	 */
+	RingBuffer_Insert(&u2c_ringbuf, byte);
+	if (motor_relay)
+		fmtx_enable();
+}
+
+static void usb_send_data(void)
+{
+	uint16_t outbytes = RingBuffer_GetCount(&c2u_ringbuf);
+
+	if (!outbytes)
+		return;
+
+	Endpoint_SelectEndpoint(vcpif.Config.DataINEndpoint.Address);
+
+	/*
+	 * Check if a packet is already enqueued to
+	 * the host - if so, we shouldn't try to send
+	 * more data until it completes as there is a
+	 * chance nothing is listening and a lengthy
+	 * timeout could occur
+	 */
+	if (!Endpoint_IsINReady())
+		return;
+
+	/*
+	 * Never send more than one bank size
+	 * less one byte to the host at a
+	 * time, so that we don't block while
+	 * a Zero Length Packet (ZLP) to
+	 * terminate the transfer is sent if
+	 * the host isn't listening */
+	outbytes = MIN(outbytes, (CDC_TXRX_EPSIZE - 1));
+
+	/*
+	 * Transfer output bytes to the USB
+	 * endpoint. Abort without dequeuing if
+	 * there is an error.
+	 */
+	while (outbytes--)
+		if (usb_send_next_byte())
+			break;
+}
+
 /*
  * Main program entry point. This routine contains the overall program
  * flow, including initial setup of
@@ -203,58 +265,8 @@ int main(void)
 
 	for (;;)
 	{
-		/*
-		 * Only try to read in bytes from the CDC interface if
-		 * the transmit buffer is not full
-		*/
-		if (!(RingBuffer_IsFull(&u2c_ringbuf))) {
-			int byte;
-
-			byte = CDC_Device_ReceiveByte(&vcpif);
-
-			/*
-			 * Store received byte into the transmit buffer, then
-			 * enable the transmit ISR if disabled
-			 */
-			if (byte >= 0) {
-				RingBuffer_Insert(&u2c_ringbuf, byte);
-				if (motor_relay)
-					fmtx_enable();
-			}
-		}
-
-		uint16_t outbytes = RingBuffer_GetCount(&c2u_ringbuf);
-		if (outbytes) {
-			Endpoint_SelectEndpoint(vcpif.Config.DataINEndpoint.Address);
-
-			/*
-			 * Check if a packet is already enqueued to
-			 * the host - if so, we shouldn't try to send
-			 * more data until it completes as there is a
-			 * chance nothing is listening and a lengthy
-			 * timeout could occur
-			 */
-			if (Endpoint_IsINReady()) {
-				/*
-				 * Never send more than one bank size
-				 * less one byte to the host at a
-				 * time, so that we don't block while
-				 * a Zero Length Packet (ZLP) to
-				 * terminate the transfer is sent if
-				 * the host isn't listening */
-				outbytes = MIN(outbytes, (CDC_TXRX_EPSIZE - 1));
-
-				/*
-				 * Transfer output bytes to the USB
-				 * endpoint. Abort without dequeuing if
-				 * there is an error.
-				 */
-				while (outbytes--)
-					if (usb_send_next_byte())
-						break;
-			}
-		}
-
+		usb_recv_data();
+		usb_send_data();
 		do_usb_task();
 	}
 }
@@ -421,4 +433,5 @@ void EVENT_CDC_Device_LineEncodingChanged(USB_ClassInfo_CDC_Device_t* const cii)
  */
 void EVENT_CDC_Device_ControLineStateChanged(USB_ClassInfo_CDC_Device_t* const cii)
 {
+	/* Currently not used */
 }

USBCAS/usbcas.h

@@ -68,7 +68,7 @@ uint32_t fmtx_real_baudrate(uint32_t baudrate);
 void fmtx_init_speed(uint32_t baudrate);
 /* Enable the TX ISR which enables sending data */
 static inline ATTR_ALWAYS_INLINE void fmtx_enable(void) {
-	/* UCSR1B |= (1 << UDRIE1); */
+	UCSR1B |= (1 << UDRIE1);
 }
 extern bool motor_relay;