diff --git a/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino b/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino
index 43a91d3..377857e 100644
--- a/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino
+++ b/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino
@@ -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__)
+ #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.
@@ -221,6 +237,19 @@ static BitBangedSPI SPI;
#endif
+#ifdef CLOCK_GEN_ENABLED
+
+// output 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);
@@ -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;
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