Avoid delay in heartbeat. That way we can also set the baudrate back to the value used in the IDE. In fact, with this fix, baud rates of up to 115200 work also.

Peter Van Hoyweghen · Peter Van Hoyweghen · commit ad2a32fd24ed · 2015-07-13T21:21:57.000+02:00
diff --git a/build/shared/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino b/build/shared/examples/11.ArduinoISP/ArduinoISP/ArduinoISP.ino
@@ -67,7 +67,7 @@
 void pulse(int pin, int times);
 
 void setup() {
-  Serial.begin(9600);
+  Serial.begin(19200);
   SPI.setDataMode(0);
   SPI.setBitOrder(MSBFIRST);
   // Clock Div can be 2,4,8,16,32,64, or 128
@@ -111,18 +111,17 @@ parameter param;
 uint8_t hbval = 128;
 int8_t hbdelta = 8;
 void heartbeat() {
-  if (hbval > 192) {
-    hbdelta = -hbdelta;
-  }
-  if (hbval < 32) {
-    hbdelta = -hbdelta;
-  }
+  static unsigned long last_time = 0;
+  unsigned long now = millis();
+  if ((now - last_time) < 40)
+    return;
+  last_time = now;
+  if (hbval > 192) hbdelta = -hbdelta;
+  if (hbval < 32) hbdelta = -hbdelta;
   hbval += hbdelta;
   analogWrite(LED_HB, hbval);
-  delay(20);
 }
 
-
 void loop(void) {
   // is pmode active?
   if (pmode) {
