Use the PDI REPEAT instruction in the PDI programmer code to reduce protocol overhead and greatly improve transfer throughput. Switch bit-bang USART in the AVRISP project to Timer 1, so that Timer 0 can be used for hardware timeouts while waiting for the NVM bus or controller to become ready.

Projects/AVRISP/Lib/NVMTarget.c

@@ -40,8 +40,10 @@
 
 void NVMTarget_SendNVMRegAddress(uint8_t Register)
 {
+	/* Determine the absolute register address from the NVM base memory address and the NVM register address */
 	uint32_t Address = XPROG_Param_NVMBase | Register;
 
+	/* Send the calculated 32-bit address to the target, LSB first */
 	PDITarget_SendByte(Address &  0xFF);
 	PDITarget_SendByte(Address >> 8);
 	PDITarget_SendByte(Address >> 16);
@@ -50,38 +52,30 @@ void NVMTarget_SendNVMRegAddress(uint8_t Register)
 
 void NVMTarget_SendAddress(uint32_t AbsoluteAddress)
 {
+	/* Send the given 32-bit address to the target, LSB first */
 	PDITarget_SendByte(AbsoluteAddress &  0xFF);
 	PDITarget_SendByte(AbsoluteAddress >> 8);
 	PDITarget_SendByte(AbsoluteAddress >> 16);
 	PDITarget_SendByte(AbsoluteAddress >> 24);
 }
 
-bool NVMTarget_WaitWhileNVMBusBusy(void)
+bool NVMTarget_WaitWhileNVMControllerBusy(void)
 {
-	uint8_t AttemptsRemaining = 255;
+	TCNT0 = 0;
 
-	/* Poll the STATUS register to check to see if NVM access has been enabled */
-	while (AttemptsRemaining--)
-	{
-		PDITarget_SendByte(PDI_CMD_LDCS | PDI_STATUS_REG);
-		if (PDITarget_ReceiveByte() & PDI_STATUS_NVM)
-		  return true;
-	}
-	
-	return false;
-}
-
-void NVMTarget_WaitWhileNVMControllerBusy(void)
-{
 	/* Poll the NVM STATUS register while the NVM controller is busy */
-	for (;;)
+	while (TCNT0 < NVM_BUSY_TIMEOUT_MS)
 	{
+		/* Send a LDS command to read the NVM STATUS register to check the BUSY flag */
 		PDITarget_SendByte(PDI_CMD_LDS | (PDI_DATSIZE_4BYTES << 2));
 		NVMTarget_SendNVMRegAddress(NVM_REG_STATUS);
 		
+		/* Check to see if the BUSY flag is still set */
 		if (!(PDITarget_ReceiveByte() & (1 << 7)))
-		  return;
+		  return true;
 	}
+	
+	return false;
 }
 
 uint32_t NVMTarget_GetMemoryCRC(uint8_t MemoryCommand)
@@ -101,18 +95,20 @@ uint32_t NVMTarget_GetMemoryCRC(uint8_t MemoryCommand)
 	PDITarget_SendByte(1 << 0);
 
 	/* Wait until the NVM bus and controller is no longer busy */
-	NVMTarget_WaitWhileNVMBusBusy();
+	PDITarget_WaitWhileNVMBusBusy();
 	NVMTarget_WaitWhileNVMControllerBusy();
 	
-	/* Read the three bytes generated CRC value */
+	/* Read the first generated CRC byte value */
 	PDITarget_SendByte(PDI_CMD_LDS | (PDI_DATSIZE_4BYTES << 2));
 	NVMTarget_SendNVMRegAddress(NVM_REG_DAT0);
 	MemoryCRC  = PDITarget_ReceiveByte();
 
+	/* Read the second generated CRC byte value */
 	PDITarget_SendByte(PDI_CMD_LDS | (PDI_DATSIZE_4BYTES << 2));
 	NVMTarget_SendNVMRegAddress(NVM_REG_DAT1);
 	MemoryCRC |= ((uint16_t)PDITarget_ReceiveByte() << 8);
 
+	/* Read the third generated CRC byte value */
 	PDITarget_SendByte(PDI_CMD_LDS | (PDI_DATSIZE_4BYTES << 2));
 	NVMTarget_SendNVMRegAddress(NVM_REG_DAT2);
 	MemoryCRC |= ((uint32_t)PDITarget_ReceiveByte() << 16);
@@ -124,15 +120,31 @@ void NVMTarget_ReadMemory(uint32_t ReadAddress, uint8_t* ReadBuffer, uint16_t Re
 {
 	NVMTarget_WaitWhileNVMControllerBusy();
 	
+	/* Send the READNVM command to the NVM controller for reading of an aribtrary location */
 	PDITarget_SendByte(PDI_CMD_STS | (PDI_DATSIZE_4BYTES << 2));
 	NVMTarget_SendNVMRegAddress(NVM_REG_CMD);
 	PDITarget_SendByte(NVM_CMD_READNVM);
 
-	/* TODO: Optimize via REPEAT and buffer orientated commands */
+	/* Send the address of the first location to read from - this also primes the internal address
-	for (uint16_t i = 0; i < ReadSize; i++)
+	 * counters so that we can use the REPEAT command later to save on overhead for multiple bytes */
-	{
 	PDITarget_SendByte(PDI_CMD_LDS | (PDI_DATSIZE_4BYTES << 2));
-		NVMTarget_SendAddress(ReadAddress++);
+	NVMTarget_SendAddress(ReadAddress);
+	*(ReadBuffer++) = PDITarget_ReceiveByte();
+
+	/* Check to see if we are reading more than a single byte */
+	if (ReadSize > 1)
+	{
+		/* Decrement the ReadSize counter as we have already read once byte of memory */
+		ReadSize--;
+	
+		/* Send the REPEAT command with the specified number of bytes remaining to read */
+		PDITarget_SendByte(PDI_CMD_REPEAT | PDI_DATSIZE_2BYTES);
+		PDITarget_SendByte(ReadSize &  0xFF);
+		PDITarget_SendByte(ReadSize >> 8);
+		
+		/* Send a LD command with indirect access and postincrement to read out the remaining bytes */
+		PDITarget_SendByte(PDI_CMD_LD | (PDI_POINTER_INDIRECT_PI << 2) | PDI_DATSIZE_1BYTE);
+		for (uint16_t i = 1; i < ReadSize; i++)
 		  *(ReadBuffer++) = PDITarget_ReceiveByte();
 	}
 }
@@ -145,6 +157,7 @@ void NVMTarget_EraseMemory(uint8_t EraseCommand, uint32_t Address)
 	NVMTarget_SendNVMRegAddress(NVM_REG_CMD);
 	PDITarget_SendByte(EraseCommand);
 	
+	/* Chip erase is handled seperately, since it's procedure is different to other erase types */
 	if (EraseCommand == NVM_CMD_CHIPERASE)
 	{
 		/* Set CMDEX bit in NVM CTRLA register to start the chip erase */
@@ -160,7 +173,8 @@ void NVMTarget_EraseMemory(uint8_t EraseCommand, uint32_t Address)
 		PDITarget_SendByte(0x00);
 	}
 	
-	NVMTarget_WaitWhileNVMBusBusy();
+	/* Wait until both the NVM bus and NVM controller are ready again */
+	PDITarget_WaitWhileNVMBusBusy();
 	NVMTarget_WaitWhileNVMControllerBusy();
 }
 

Projects/AVRISP/Lib/NVMTarget.h

@@ -56,12 +56,7 @@
 		#endif
 
 	/* Defines: */
-		#define FLASH_BASE                     0x00800000
+		#define NVM_BUSY_TIMEOUT_MS            200
-		#define EPPROM_BASE                    0x008C0000
-		#define FUSE_BASE                      0x008F0020
-		#define DATAMEM_BASE                   0x01000000
-		#define PROD_SIGNATURE_BASE            0x008E0200
-		#define USER_SIGNATURE_BASE            0x008E0400
 		
 		#define NVM_REG_ADDR0                  0x00
 		#define NVM_REG_ADDR1                  0x01
@@ -113,8 +108,7 @@
 	/* Function Prototypes: */
 		void     NVMTarget_SendNVMRegAddress(uint8_t Register);
 		void     NVMTarget_SendAddress(uint32_t AbsoluteAddress);
-		bool     NVMTarget_WaitWhileNVMBusBusy(void);
+		bool     NVMTarget_WaitWhileNVMControllerBusy(void);
-		void     NVMTarget_WaitWhileNVMControllerBusy(void);
 		uint32_t NVMTarget_GetMemoryCRC(uint8_t MemoryCommand);
 		void     NVMTarget_ReadMemory(uint32_t ReadAddress, uint8_t* ReadBuffer, uint16_t ReadSize);
 		void     NVMTarget_EraseMemory(uint8_t EraseCommand, uint32_t Address);

Projects/AVRISP/Lib/PDIProtocol.c

@@ -114,7 +114,7 @@ static void PDIProtocol_EnterXPROGMode(void)
 	  PDITarget_SendByte(PDI_NVMENABLE_KEY[i - 1]);
 
 	/* Wait until the NVM bus becomes active */
-	bool NVMBusEnabled = NVMTarget_WaitWhileNVMBusBusy();
+	bool NVMBusEnabled = PDITarget_WaitWhileNVMBusBusy();
 	
 	Endpoint_Write_Byte(CMD_XPROG);
 	Endpoint_Write_Byte(XPRG_CMD_ENTER_PROGMODE);

Projects/AVRISP/Lib/PDITarget.c

@@ -44,7 +44,7 @@ volatile bool     IsSending;
 volatile uint16_t SoftUSART_Data;
 volatile uint8_t  SoftUSART_BitCount;
 
-ISR(TIMER0_COMPA_vect, ISR_BLOCK)
+ISR(TIMER1_COMPA_vect, ISR_BLOCK)
 {
 	/* Toggle CLOCK pin in a single cycle (see AVR datasheet) */
 	BITBANG_PDICLOCK_PIN |= BITBANG_PDICLOCK_MASK;
@@ -112,11 +112,10 @@ void PDITarget_EnableTargetPDI(void)
 	asm volatile ("NOP"::);
 	asm volatile ("NOP"::);
 
-	/* Fire timer compare ISR every 50 cycles to manage the software USART */
+	/* Fire timer compare ISR every 100 cycles to manage the software USART */
-	OCR0A   = 50;
+	OCR1A   = 100;
-	TCCR0A  = (1 << WGM01);
+	TCCR1B  = (1 << WGM12) | (1 << CS10);
-	TCCR0B  = (1 << CS00);
+	TIMSK1  = (1 << OCIE1A);
-	TIMSK0  = (1 << OCIE0A);
 	
 	PDITarget_SendBreak();
 	PDITarget_SendBreak();
@@ -275,4 +274,20 @@ void PDITarget_SendBreak(void)
 #endif
 }
 
+bool PDITarget_WaitWhileNVMBusBusy(void)
+{
+	TCNT0 = 0;
+
+	/* Poll the STATUS register to check to see if NVM access has been enabled */
+	while (TCNT0 < PDI_NVM_TIMEOUT_MS)
+	{
+		/* 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;
+	}
+	
+	return false;
+}
+
 #endif

Projects/AVRISP/Lib/PDITarget.h

@@ -69,6 +69,8 @@
 		
 		#define BITS_IN_FRAME            12
 		
+		#define PDI_NVM_TIMEOUT_MS       200
+		
 		#define PDI_CMD_LDS              0x00
 		#define PDI_CMD_LD               0x20
 		#define PDI_CMD_STS              0x40
@@ -102,5 +104,6 @@
 		void    PDITarget_SendByte(uint8_t Byte);
 		uint8_t PDITarget_ReceiveByte(void);
 		void    PDITarget_SendBreak(void);
+		bool    PDITarget_WaitWhileNVMBusBusy(void);
 
 #endif