Make software USART used in the XPLAINBridge project directly check and store...

Make software USART used in the XPLAINBridge project directly check and store into the ring buffers, rather than polling from the main program loop to avoid added latency.

Projects/XPLAINBridge/Lib/LightweightRingBuff.h

@@ -53,6 +53,7 @@
 			RingBuff_Data_t  Buffer[BUFFER_SIZE];
 			RingBuff_Data_t* In;
 			RingBuff_Data_t* Out;
+			uint8_t          Count;
 		} RingBuff_t;
 	
 	/* Inline Functions: */
@@ -60,6 +61,7 @@
 		{
 			Buffer->In  = Buffer->Buffer;
 			Buffer->Out = Buffer->Buffer;
+			Buffer->Count = 0;
 		}
 		
 		static inline void RingBuffer_Insert(RingBuff_t* const Buffer, RingBuff_Data_t Data)
@@ -68,6 +70,8 @@
 		
 			if (++Buffer->In == &Buffer->Buffer[BUFFER_SIZE])
 			  Buffer->In = Buffer->Buffer;
+			  
+			Buffer->Count++;
 		}
 
 		static inline RingBuff_Data_t RingBuffer_Remove(RingBuff_t* const Buffer)
@@ -77,12 +81,9 @@
 			if (++Buffer->Out == &Buffer->Buffer[BUFFER_SIZE])
 			  Buffer->Out = Buffer->Buffer;
 			  
-			return Data;
-		}
+			Buffer->Count--;
 
-		static inline bool RingBuffer_Empty(RingBuff_t* const Buffer)
-		{
-			return (Buffer->In == Buffer->Out);
+			return Data;
 		}
 
 #endif

Projects/XPLAINBridge/Lib/SoftUART.c

@@ -30,27 +30,16 @@
   this software.
 */
 
-#include "SoftUART.h"
-
-volatile bool    srx_done;
-volatile uint8_t stx_count;
-static   uint8_t srx_data, srx_mask, srx_tmp, stx_data;
-
-void SoftUART_TxByte(uint8_t Byte)
-{
-	while (stx_count);
+/** \file
+ *
+ *  Software UART for both data transmission and reception. This
+ *  code continuously monitors the ring buffers set up by the main
+ *  project source file and reads/writes data as it becomes available.
+ */
 
-	stx_data  = ~Byte;
-	stx_count = 10;
-}
-
-uint8_t SoftUART_RxByte(void)
-{
-	while (!(srx_done));
-	srx_done = false;
+#include "SoftUART.h"
 
-	return srx_data;
-}
+static uint8_t TX_BitsRemaining, TX_Data, RX_BitMask, RX_Data;
 
 void SoftUART_Init(void)
 {
@@ -61,8 +50,7 @@ void SoftUART_Init(void)
 	EICRA  = (1 << ISC01);					// -ve edge
 	EIMSK  = (1 << INT0);					// enable INT0 interrupt
 
-	stx_count = 0;							// nothing to send
-	srx_done  = false;						// nothing received
+	TX_BitsRemaining = 0;					// nothing to send
 	STXPORT |= (1 << STX);					// TX output
 	STXDDR  |= (1 << STX);					// TX output
 	SRXPORT |= (1 << SRX);					// pullup on INT0
@@ -73,8 +61,8 @@ ISR(INT0_vect)
 {
 	OCR2A = TCNT2 + (BIT_TIME / 8 * 3 / 2);	// scan 1.5 bits after start
 
-	srx_tmp  = 0;							// clear bit storage
-	srx_mask = 1;							// bit mask
+	RX_Data    = 0;							// clear bit storage
+	RX_BitMask = (1 << 0);					// bit mask
 
 	TIFR2 = (1 << OCF2A);					// clear pending interrupt
 
@@ -88,19 +76,19 @@ ISR(INT0_vect)
 /* ISR to manage the reception of bits to the transmitter. */
 ISR(TIMER2_COMPA_vect)
 {
-	if (srx_mask)
+	if (RX_BitMask)
 	{
 		if (SRXPIN & (1 << SRX))
-		  srx_tmp |= srx_mask;
+		  RX_Data |= RX_BitMask;
 
-		srx_mask <<= 1;
+		RX_BitMask <<= 1;
 
 		OCR2A += BIT_TIME / 8;				// next bit slice
 	}
 	else
 	{
-		srx_done  = true;					// mark rx data valid
-		srx_data  = srx_tmp;				// store rx data
+		RingBuffer_Insert(&UARTtoUSB_Buffer, RX_Data);
+
 		TIMSK2    = (1 << OCIE2B);			// enable tx and wait for start
 		EIMSK    |= (1 << INT0);			// enable START irq
 		EIFR      = (1 << INTF0);			// clear any pending
@@ -112,20 +100,25 @@ ISR(TIMER2_COMPB_vect)
 {
 	OCR2B += BIT_TIME / 8;					// next bit slice
 
-	if (stx_count)
+	if (TX_BitsRemaining)
 	{
-		if (--stx_count != 9)				// no start bit
+		if (--TX_BitsRemaining != 9)		// no start bit
 		{
-			if (!(stx_data & 1))			// test inverted data
-			  TCCR2A = (1 << COM2B1) | (1 << COM2B0);
-			else
+			if (TX_Data & (1 << 0))			// test inverted data
 			  TCCR2A = (1 << COM2B1);
+			else
+			  TCCR2A = (1 << COM2B1) | (1 << COM2B0);
 
-			stx_data >>= 1;					// shift zero in from left
+			TX_Data >>= 1;					// shift zero in from left
 		}
 		else
 		{
 			TCCR2A = (1 << COM2B1);			// START bit
 		}
 	}
+	else if (USBtoUART_Buffer.Count)
+	{
+		TX_Data = ~RingBuffer_Remove(&USBtoUART_Buffer);
+		TX_BitsRemaining = 10;
+	}
 } 

Projects/XPLAINBridge/Lib/SoftUART.h

@@ -38,6 +38,9 @@
 		#include <avr/interrupt.h>
 		#include <stdbool.h>
 		
+		#include "../XPLAINBridge.h"
+		#include "LightweightRingBuff.h"
+
 	/* Macros: */
 		#define BAUD       9600
 		#define BIT_TIME   (uint16_t)((F_CPU + (BAUD / 2)) / BAUD)
@@ -50,24 +53,7 @@
 		#define STXPORT    PORTD
 		#define STXDDR     DDRD
 
-	/* External Variables: */
-		extern volatile bool    srx_done;
-		extern volatile uint8_t stx_count;
-
-	/* Inline Functions: */
-		static inline bool SoftUART_IsReady(void)
-		{
-			return !(stx_count);
-		}
-
-		static inline bool SoftUART_IsReceived(void)
-		{
-			return srx_done;
-		}
-
 	/* Function Prototypes: */
-		void    SoftUART_TxByte(uint8_t c);
-		uint8_t SoftUART_RxByte(void);
 		void    SoftUART_Init(void);
 
 #endif
\ No newline at end of file

Projects/XPLAINBridge/XPLAINBridge.c

@@ -125,17 +125,9 @@ void USARTBridge_Task(void)
 	  RingBuffer_Insert(&USBtoUART_Buffer, CDC_Device_ReceiveByte(&VirtualSerial_CDC_Interface));
 	
 	/* Read bytes from the UART receive buffer into the USB IN endpoint */
-	if (!(RingBuffer_Empty(&UARTtoUSB_Buffer)))
+	if (UARTtoUSB_Buffer.Count)
 	  CDC_Device_SendByte(&VirtualSerial_CDC_Interface, RingBuffer_Remove(&UARTtoUSB_Buffer));
 	  
-	/* Load bytes from the UART transmit buffer into the UART */
-	if (!(RingBuffer_Empty(&USBtoUART_Buffer)) && SoftUART_IsReady())
-	  SoftUART_TxByte(RingBuffer_Remove(&USBtoUART_Buffer));
-	
-	/* Load bytes from the UART into the UART receive buffer */
-	if (SoftUART_IsReceived())
-	  RingBuffer_Insert(&UARTtoUSB_Buffer, SoftUART_RxByte());
-
 	CDC_Device_USBTask(&VirtualSerial_CDC_Interface);
 }
 

Projects/XPLAINBridge/XPLAINBridge.h

@@ -78,6 +78,8 @@
 
 	/* External Variables: */
 		extern bool       CurrentFirmwareMode;
+		extern RingBuff_t UARTtoUSB_Buffer;
+		extern RingBuff_t USBtoUART_Buffer;
 		
 	/* Function Prototypes: */
 		void SetupHardware(void);