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ArduinoISP: Add an option to enable a 4 MHz clock signal on pin 3 #17

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ArduinoISP: Add an option to enable a 4 MHz clock signal on pin 3 #17

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5c47f87
Add an option on Uno boards to enable a 4 MHz clock signal on pin 3
pr1csynth Apr 7, 2019
d8d24c7
Make ArduinoISP code formatting compliant with examples_formatter.conf
per1234 Sep 26, 2020
96cd102
Correct misspelled word in ArduinoISP comment
per1234 Sep 26, 2020
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33 changes: 33 additions & 0 deletions examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,22 @@
#define SPI_CLOCK (1000000/6)


// With an Genuino/Uno board, uncomment following line to generate a 4 MHz clock
// signal on pin 3 (only available on Uno / ATmega*8)
//
// Can be useful to recover an AVR chip with fuses setup for an external clock

// #define ENABLE_CLOCK_GEN

#ifdef ENABLE_CLOCK_GEN

#if defined(__AVR_ATmega328__) || defined(__AVR_ATmega328P__) || defined(__AVR_ATmega168__) || defined(__AVR_ATmega88__)
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@per1234 per1234 Sep 26, 2020 •
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@facchinm requested changes on 2019-04-18

ArduinoISP sketch is meant to run on all Arduinos (also the ones with ARM chips), so it would be nice to keep the sketch functionalities in sync between all the targets.

#define CLOCK_GEN_ENABLED
#endif

#endif


// Select hardware or software SPI, depending on SPI clock.
// Currently only for AVR, for other architectures (Due, Zero,...), hardware SPI
// is probably too fast anyway.
Expand Down Expand Up @@ -221,6 +237,19 @@ static BitBangedSPI SPI;

#endif

#ifdef CLOCK_GEN_ENABLED

// ouput a 4MHz clock on pin 3 (Uno) using fast PWM
void setup_clock_gen(){
pinMode(3, OUTPUT);
TCCR2A = 0x23;
TCCR2B = 0x09;
OCR2A = 3;
OCR2B = 1;
}

#endif

void setup() {
SERIAL.begin(BAUDRATE);

Expand All @@ -231,6 +260,10 @@ void setup() {
pinMode(LED_HB, OUTPUT);
pulse(LED_HB, 2);

#ifdef CLOCK_GEN_ENABLED
setup_clock_gen();
#endif

}

int ISPError = 0;
Expand Down