Rescue clock of the AVRISP-MKII moved to the AVR's OCR1A pin, so that the clock can be generated at all times when 125KHz ISP programming mode is selected.

5 files changed, 50 insertions, 20 deletions

diff --git a/Projects/AVRISP-MKII/AVRISP-MKII.txt b/Projects/AVRISP-MKII/AVRISP-MKII.txt
index e36ffe231..534af5639 100644
--- a/Projects/AVRISP-MKII/AVRISP-MKII.txt
+++ b/Projects/AVRISP-MKII/AVRISP-MKII.txt
@@ -105,9 +105,9 @@
  *   </tr>
  *  </table>
  *
- *  In addition, the AVR's XCK pin will generate a .5MHz clock when SPI programming is used, to act as an external
- *  device clock if the fuses have been mis-set. To use the recovery clock, connect XCK to the target AVR's XTAL1
- *  pin, and set the ISP programming speed to 125KHz or below.
+ *  In addition, the AVR's OCR1A pin will generate a .5MHz clock, to act as an external rescue device clock
+ *  if the fuses have been mis-set. To use the recovery clock, connect the OCR1A pin of the USB AVR to the target
+ *  AVR's XTAL1 pin, and set the ISP programming speed to 125KHz (note: other ISP speeds will not work correctly).
  *
  *  <b><sup>1</sup></b> <i>Optional, see \ref SSec_Options section - for USB AVRs with ADC modules only</i> \n
  *  <b><sup>2</sup></b> <i>See AUX line related tokens in the \ref SSec_Options section</i>
diff --git a/Projects/AVRISP-MKII/Lib/ISP/ISPProtocol.c b/Projects/AVRISP-MKII/Lib/ISP/ISPProtocol.c
index 30d45c916..9056942d2 100644
--- a/Projects/AVRISP-MKII/Lib/ISP/ISPProtocol.c
+++ b/Projects/AVRISP-MKII/Lib/ISP/ISPProtocol.c
@@ -64,12 +64,6 @@ void ISPProtocol_EnterISPMode(void)
 
 	CurrentAddress = 0;
 
-	/* Set up the synchronous USART to generate the .5MHz recovery clock on XCK pin */
-	UBRR1  = (F_CPU / 500000UL);
-	UCSR1B = (1 << TXEN1);
-	UCSR1C = (1 << UMSEL10) | (1 << UPM11) | (1 << USBS1) | (1 << UCSZ11) | (1 << UCSZ10) | (1 << UCPOL1);
-	DDRD  |= (1 << 5);
-
 	/* Perform execution delay, initialize SPI bus */
 	ISPProtocol_DelayMS(Enter_ISP_Params.ExecutionDelayMS);
 	ISPTarget_Init();
@@ -127,12 +121,6 @@ void ISPProtocol_LeaveISPMode(void)
 	ISPTarget_ShutDown();
 	ISPProtocol_DelayMS(Leave_ISP_Params.PostDelayMS);
 
-	/* Turn off the synchronous USART to terminate the recovery clock on XCK pin */
-	UBRR1  = (F_CPU / 500000UL);
-	UCSR1B = (1 << TXEN1);
-	UCSR1C = (1 << UMSEL10) | (1 << UPM11) | (1 << USBS1) | (1 << UCSZ11) | (1 << UCSZ10) | (1 << UCPOL1);
-	DDRD  &= ~(1 << 5);
-
 	Endpoint_Write_Byte(CMD_LEAVE_PROGMODE_ISP);
 	Endpoint_Write_Byte(STATUS_CMD_OK);
 	Endpoint_ClearIN();
diff --git a/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.c b/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.c
index e596cfe28..fe2f50d07 100644
--- a/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.c
+++ b/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.c
@@ -119,7 +119,7 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
 {
 	if (!(PINB & (1 << 1)))
 	{
-		if (SoftSPI_Data & 0x80)
+		if (SoftSPI_Data & (1 << 7))
 		  PORTB |=  (1 << 2);
 		else
 		  PORTB &= ~(1 << 2);
@@ -132,10 +132,11 @@ ISR(TIMER1_COMPA_vect, ISR_BLOCK)
 		  TCCR1B = 0;
 
 		if (PINB & (1 << 3))
-		  SoftSPI_Data |= 0x01;
+		  SoftSPI_Data |= (1 << 0);
 	}
 
-	PORTB ^= (1 << 1);
+	/* Fast toggle of PORTB.1 via the PIN register (see datasheet) */
+	PINB |= (1 << 1);
 }
 
 /** Initialises the appropriate SPI driver (hardware or software, depending on the selected ISP speed) ready for
@@ -159,8 +160,7 @@ void ISPTarget_Init(void)
 		DDRB  |= ((1 << 1) | (1 << 2));
 		PORTB |= ((1 << 0) | (1 << 3));
 
-		TIMSK1 = (1 << OCIE1A);
-		OCR1A  = pgm_read_word(&TimerCompareFromSCKDuration[SCKDuration - sizeof(SPIMaskFromSCKDuration)]);
+		ISPTarget_ConfigureSoftwareISP(SCKDuration);
 	}
 }
 
@@ -177,9 +177,48 @@ void ISPTarget_ShutDown(void)
 	{
 		DDRB  &= ~((1 << 1) | (1 << 2));
 		PORTB &= ~((1 << 0) | (1 << 3));
+		
+		ISPTarget_ConfigureRescueClock();
 	}
 }
 
+/** Configures the AVR to produce a .5MHz rescue clock out of the OCR1A pin of the AVR, so
+ *  that it can be fed into the XTAL1 pin of an AVR whose fuses have been misconfigured for
+ *  an external clock rather than a crystal. When used, the ISP speed must be 125KHz for this
+ *  functionality to work correctly.
+ */
+void ISPTarget_ConfigureRescueClock(void)
+{
+	/* Configure OCR1A as an output for the specified AVR model */
+	#if defined(USB_SERIES_2_AVR)
+	DDRC |= (1 << 6);
+	#else
+	DDRB |= (1 << 5);
+	#endif
+
+	/* Start Timer 1 to generate a .5MHz clock on the OCR1A pin */
+	TIMSK1 = 0;
+	TCNT1  = 0;
+	OCR1A  = (F_CPU / 2 / 500000UL);
+	TCCR1A = (1 << COM1A0);
+	TCCR1B = ((1 << WGM12) | (1 << CS10));
+}
+
+/** Configures the AVR's timer ready to produce software ISP for the slower ISP speeds that
+ *  cannot be obtained when using the AVR's hardware SPI module.
+ *
+ *  \param[in] SCKDuration  Duration of the desired software ISP SCK clock
+ */
+void ISPTarget_ConfigureSoftwareISP(const uint8_t SCKDuration)
+{
+	/* Configure Timer 1 for software ISP using the specified SCK duration */
+	TIMSK1 = (1 << OCIE1A);
+	TCNT1  = 0;
+	OCR1A  = pgm_read_word(&TimerCompareFromSCKDuration[SCKDuration - sizeof(SPIMaskFromSCKDuration)]);
+	TCCR1A = 0;
+	TCCR1B = 0;
+}
+
 /** Sends and receives a single byte of data to and from the attached target via software SPI.
  *
  *  \param[in] Byte  Byte of data to send to the attached target
diff --git a/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.h b/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.h
index e6ee42d4e..c467298c6 100644
--- a/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.h
+++ b/Projects/AVRISP-MKII/Lib/ISP/ISPTarget.h
@@ -68,6 +68,8 @@
 	/* Function Prototypes: */
 		void    ISPTarget_Init(void);
 		void    ISPTarget_ShutDown(void);
+		void    ISPTarget_ConfigureRescueClock(void);
+		void    ISPTarget_ConfigureSoftwareISP(const uint8_t SCKDuration);
 		uint8_t ISPTarget_TransferSoftSPIByte(const uint8_t Byte);
 		void    ISPTarget_ChangeTargetResetLine(const bool ResetTarget);
 		uint8_t ISPTarget_WaitWhileTargetBusy(void);
diff --git a/Projects/AVRISP-MKII/Lib/V2Protocol.c b/Projects/AVRISP-MKII/Lib/V2Protocol.c
index 673a0941c..208d7b77e 100644
--- a/Projects/AVRISP-MKII/Lib/V2Protocol.c
+++ b/Projects/AVRISP-MKII/Lib/V2Protocol.c
@@ -66,6 +66,7 @@ void V2Protocol_Init(void)
 	TIMSK0 = (1 << OCIE0A);
 
 	V2Params_LoadNonVolatileParamValues();
+	ISPTarget_ConfigureRescueClock();
 }
 
 /** Master V2 Protocol packet handler, for received V2 Protocol packets from a connected host.