Avoid underruns as much as possible

USBCAS/fmrx.c

@@ -6,12 +6,12 @@
 
 static inline void fmrx_led_on(void)
 {
-	PORTB &= ~(1 << 0);
+  //PORTB &= ~(1 << 0);
 }
 
 static inline void fmrx_led_off(void)
 {
-	PORTB |= (1 << 0);
+  //	PORTB |= (1 << 0);
 }
 
 void fmrx_init(void)

USBCAS/fmtx.c

@@ -16,6 +16,7 @@
 static inline ATTR_ALWAYS_INLINE void fmtx_disable(void)
 {
 	UCSR1B &= ~(1 << UDRIE1);
+	PORTB |= (1 << 0);
 }
 
 static uint8_t parity;
@@ -31,20 +32,17 @@ ISR(USART1_UDRE_vect)
 	if (!left) {
 		/* Fetch a new byte if there is one, unless motor is off */
 		int nd;
-		nd = motor_relay ? fmtx_next_byte() : -1;
-		if (nd < 0) {
+		if (!motor_relay() || (nd = fmtx_next_byte()) < 0) {
 			/*
 			 * Nothing to send.  Hold the line for some
 			 * number of byte-times in case we suffered an
 			 * underrun. Afterwards, the hardware will
 			 * drive the line high.
 			 */
-			if (++gap) {
-				UCSR1A = TX_IDLE;
-				UCSR1A = parity;
-			} else {
+			UCSR1A = TX_IDLE;
+			UCSR1A = parity;
+			if (!++gap)
 				fmtx_disable();
-			}
 			return;
 		}
 		data = nd;
@@ -68,7 +66,7 @@ void fmtx_drain(void)
 {
 	/* Wait until input queue is idle and we have had at least one output */
 	while ((UCSR1B & (1 << UDRIE1)) || !(UCSR1A & TX_IDLE))
-		do_usb_task();
+		do_usb_tasks();
 }
 
 /*
@@ -96,12 +94,11 @@ void fmtx_init_speed(uint32_t baudrate)
 {
 	parity = 0xff;		/* 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 |= 0x28; /* Drive data and clock high while idle */
 
+	UCSR1B = 0;		/* Disable transmitter and ISR */
+
 	/*
 	 * SPI master mode, mode 1, LSB first
 	 * UCPHA doesn't matter, but have UCPOL=1 to that the clock

USBCAS/usbcas.c

@@ -109,20 +109,30 @@ static void motor_sense_init(void)
 	TCCR3B = (3 << WGM32)|(2 << CS30); /* fosc/8, CTC mode, TOP=ICR3 */
 }
 
-bool motor_relay;
+bool _motor_relay;
+
+static inline ATTR_ALWAYS_INLINE void motor_led_on(void)
+{
+  //PORTB &= ~(1 << 0);
+}
+
+static inline ATTR_ALWAYS_INLINE void motor_led_off(void)
+{
+  //PORTB |= (1 << 0);
+}
 
 ISR(TIMER3_CAPT_vect)
 {
 	static uint8_t relay_ctr;
-	bool relay;
 
-	if (!(PORTD & 2) || (EIFR & 2)) {
+	if (!(PIND & 1) || (EIFR & 2)) {
 		/* Relay active */
 		EIFR = 2;	/* Clear edge detect */
 		if (relay_ctr < 16) {
 			relay_ctr++;
-		} else if (!motor_relay) {
-			motor_relay = true;
+		} else if (!_motor_relay) {
+			_motor_relay = true;
+			motor_led_on();
 			fmtx_enable();
 		}
 	} else {
@@ -130,7 +140,8 @@ ISR(TIMER3_CAPT_vect)
 		if (relay_ctr) {
 			relay_ctr--;
 		} else {
-			motor_relay = false;
+			_motor_relay = false;
+			motor_led_off();
 		}
 	}
 }
@@ -145,7 +156,7 @@ static void update_modem_status(USB_ClassInfo_CDC_Device_t * const cii,
 {
 	uint16_t lines = 0;
 
-	if (motor_relay) /* Cassette relay active */
+	if (motor_relay()) /* Cassette relay active */
 		lines |= CDC_CONTROL_LINE_IN_DCD | CDC_CONTROL_LINE_IN_DSR;
 
 	if (forced || cii->State.ControlLineStates.DeviceToHost != lines) {
@@ -158,7 +169,7 @@ static void update_modem_status(USB_ClassInfo_CDC_Device_t * const cii,
  * This is called in the main loop, but also any time we are busy-waiting
  * on something.
  */
-void do_usb_task(void)
+static void usb_run_stack(void)
 {
 	/* Update modem flags if needed */
 	update_modem_status(&vcpif, false);
@@ -189,25 +200,27 @@ static bool usb_send_next_byte(void)
 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)
+	uint8_t nbytes = CDC_TXRX_EPSIZE - 1; /* Max bytes to receive */
+
+	while (nbytes--) {
+		/*
+		 * 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);
 		fmtx_enable();
+	}
 }
 
 static void usb_send_data(void)
@@ -248,6 +261,13 @@ static void usb_send_data(void)
 			break;
 }
 
+void do_usb_tasks(void)
+{
+	usb_recv_data();
+	usb_send_data();
+	usb_run_stack();
+}
+
 /*
  * Main program entry point. This routine contains the overall program
  * flow, including initial setup of
@@ -263,11 +283,8 @@ int main(void)
 
 	GlobalInterruptEnable();
 
-	for (;;)
-	{
-		usb_recv_data();
-		usb_send_data();
-		do_usb_task();
+	while (1) {
+		do_usb_tasks();
 	}
 }
 
@@ -305,7 +322,7 @@ void SetupHardware(void)
 
 	/*
 	 * PORT C:
-	 *   PC6 - NC
+	 *   PC6 - DIN pin 3 (ABC800 data out)
 	 *   PC7 - NP
 	 */
 	DDRC  = 0x80;
@@ -313,7 +330,7 @@ void SetupHardware(void)
 
 	/*
 	 * PORT D:
-	 *   PD0 - data in (alt)
+	 *   PD0 - motor sense unused (GND)
 	 *   PD1 - motor sense#
 	 *   PD2 - NC
 	 *   PD3 - data out
@@ -340,7 +357,7 @@ void SetupHardware(void)
 	 *   PF4 - NC
 	 *   PF5 - NC
 	 *   PF6 - NC
-	 *   PF7 - NC
+	 *   PF7 - DIN pin 4 (ABC800 motor sense#)
 	 */
 	DDRF  = 0x03;
 	PORTF = 0xf0;
@@ -353,7 +370,7 @@ void SetupHardware(void)
 
 	/* Initialize receiver and transmitter */
 	fmrx_init();
-	current_baudrate = fmtx_real_baudrate(0);
+	current_baudrate = fmtx_real_baudrate(CAS_BAUDRATE_ABC80);
 	fmrx_set_speed(current_baudrate);
 	fmtx_init_speed(current_baudrate);
 }
@@ -415,8 +432,7 @@ void EVENT_CDC_Device_LineEncodingChanged(USB_ClassInfo_CDC_Device_t* const cii)
 	uint32_t baudrate = cii->State.LineEncoding.BaudRateBPS;
 
 	/* This is a hack to give a sensible default */
-	if (baudrate == 9600)
-		baudrate = CAS_BAUDRATE_ABC80;
+	baudrate = CAS_BAUDRATE_ABC80;
 
 	baudrate = fmtx_real_baudrate(baudrate);
 

USBCAS/usbcas.h

@@ -52,7 +52,7 @@
 
 /* Function Prototypes: */
 void SetupHardware(void);
-void do_usb_task(void);
+void do_usb_tasks(void);
 
 void EVENT_USB_Device_Connect(void);
 void EVENT_USB_Device_Disconnect(void);
@@ -67,10 +67,17 @@ void fmtx_drain(void);
 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) {
+static inline ATTR_ALWAYS_INLINE void fmtx_enable(void)
+{
 	UCSR1B |= (1 << UDRIE1);
+	PORTB &= ~(1 << 0);
+}
+extern bool _motor_relay;
+
+static inline ATTR_ALWAYS_INLINE bool motor_relay(void)
+{
+	return _motor_relay;
 }
-extern bool motor_relay;
 
 void fmrx_init(void);
 void fmrx_set_speed(uint32_t baudrate);