X-Git-Url: http://git.linex4red.de/pub/USBasp.git/blobdiff_plain/4f74075fad7f1e7a35d04ff534d9d6a57d2b97fc..24f730fce3f2022762011d795c3feada5ef874b3:/Projects/AVRISP/Lib/PDITarget.c

diff --git a/Projects/AVRISP/Lib/PDITarget.c b/Projects/AVRISP/Lib/PDITarget.c
index 1bbb4d577..29bb33985 100644
--- a/Projects/AVRISP/Lib/PDITarget.c
+++ b/Projects/AVRISP/Lib/PDITarget.c
@@ -39,14 +39,15 @@
 #if defined(ENABLE_PDI_PROTOCOL) || defined(__DOXYGEN__)
 
 /** Flag to indicate if the USART is currently in Tx or Rx mode. */
-volatile bool     IsSending;
+volatile bool               IsSending;
 
 #if !defined(PDI_VIA_HARDWARE_USART)
 /** Software USART raw frame bits for transmission/reception. */
-volatile uint16_t SoftUSART_Data;
+volatile uint16_t           SoftUSART_Data;
 
 /** Bits remaining to be sent or received via the software USART - set as a GPIOR for speed. */
-#define SoftUSART_BitCount   GPIOR2
+#define SoftUSART_BitCount  GPIOR2
+
 
 /** ISR to manage the software USART when bit-banged USART mode is selected. */
 ISR(TIMER1_COMPA_vect, ISR_BLOCK)
@@ -69,8 +70,10 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
 		if ((SoftUSART_BitCount == BITS_IN_FRAME) && (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK))
 		  return;
 	
+		/* Shift in the bit one less than the frame size in position, so that the start bit will eventually
+		 * be discarded leaving the data to be byte-aligned for quick access */
 		if (BITBANG_PDIDATA_PIN & BITBANG_PDIDATA_MASK)
-		  SoftUSART_Data |= (1 << BITS_IN_FRAME);
+		  SoftUSART_Data |= (1 << (BITS_IN_FRAME - 1));
 
 		SoftUSART_Data >>= 1;
 		SoftUSART_BitCount--;
@@ -81,6 +84,7 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
 		if (!IsSending)
 		  return;
 
+		/* Set the data line to the next bit value */
 		if (SoftUSART_Data & 0x01)
 		  BITBANG_PDIDATA_PORT |=  BITBANG_PDIDATA_MASK;
 		else
@@ -163,7 +167,7 @@ void PDITarget_DisableTargetPDI(void)
  *
  *  \param[in] Byte  Byte to send through the USART
  */
-void PDITarget_SendByte(uint8_t Byte)
+void PDITarget_SendByte(const uint8_t Byte)
 {
 #if defined(PDI_VIA_HARDWARE_USART)
 	/* Switch to Tx mode if currently in Rx mode */
@@ -192,20 +196,22 @@ void PDITarget_SendByte(uint8_t Byte)
 		IsSending = true;
 	}
 
-	bool    EvenParityBit = false;
-	uint8_t ParityData    = Byte;
+	/* Calculate the new USART frame data here while while we wait for a previous byte (if any) to finish sending */
+	uint16_t NewUSARTData = ((1 << 11) | (1 << 10) | (0 << 9) | ((uint16_t)Byte << 1) | (0 << 0));
 
-	/* Compute Even parity bit */
-	for (uint8_t i = 0; i < 8; i++)
+	/* Compute Even parity - while a bit is still set, chop off lowest bit and toggle parity bit */
+	uint8_t ParityData    = Byte;
+	while (ParityData)
 	{
-		EvenParityBit ^= ParityData & 0x01;
-		ParityData    >>= 1;
+		NewUSARTData ^= (1 << 9);
+		ParityData   &= (ParityData - 1);
 	}
 
+	/* Wait until transmitter is idle before writing new data */
 	while (SoftUSART_BitCount);
 
 	/* Data shifted out LSB first, START DATA PARITY STOP STOP */
-	SoftUSART_Data     = ((uint16_t)EvenParityBit << 9) | ((uint16_t)Byte << 1) | (1 << 10) | (1 << 11);
+	SoftUSART_Data     = NewUSARTData;
 	SoftUSART_BitCount = BITS_IN_FRAME;
 #endif
 }
@@ -251,8 +257,8 @@ uint8_t PDITarget_ReceiveByte(void)
 	SoftUSART_BitCount = BITS_IN_FRAME;
 	while (SoftUSART_BitCount);
 	
-	/* Throw away the start, parity and stop bits to leave only the data */
-	return (uint8_t)(SoftUSART_Data >> 1);
+	/* Throw away the parity and stop bits to leave only the data (start bit is already discarded) */
+	return (uint8_t)SoftUSART_Data;
 #endif
 }
 
@@ -273,7 +279,7 @@ void PDITarget_SendBreak(void)
 	}
 
 	/* Need to do nothing for a full frame to send a BREAK */
-	for (uint8_t i = 0; i <= BITS_IN_FRAME; i++)
+	for (uint8_t i = 0; i < BITS_IN_FRAME; i++)
 	{
 		/* Wait for a full cycle of the clock */
 		while (PIND & (1 << 5));
@@ -305,14 +311,23 @@ void PDITarget_SendBreak(void)
 bool PDITarget_WaitWhileNVMBusBusy(void)
 {
 	TCNT0 = 0;
-
+	TIFR0 = (1 << OCF1A);
+			
+	uint8_t TimeoutMS = PDI_NVM_TIMEOUT_MS;
+	
 	/* Poll the STATUS register to check to see if NVM access has been enabled */
-	while (TCNT0 < PDI_NVM_TIMEOUT_MS)
+	while (TimeoutMS)
 	{
 		/* Send the LDCS command to read the PDI STATUS register to see the NVM bus is active */
 		PDITarget_SendByte(PDI_CMD_LDCS | PDI_STATUS_REG);
 		if (PDITarget_ReceiveByte() & PDI_STATUS_NVM)
 		  return true;
+
+		if (TIFR0 & (1 << OCF1A))
+		{
+			TIFR0 = (1 << OCF1A);
+			TimeoutMS--;
+		}
 	}
 	
 	return false;