Serial.println() hangs in ISR

Projects Programming
1

I have a ISR which handles keyboard inputs via a MCP23S17 I/O expander.
I use the Serial.println() to send debug messages within my keyboard ISR.
The problem is if I have more than 3 calls to Serial.println() the whole program hangs!!!

any ideas as to why this happens???

2

So, did you connect the 23S17 to an external interrupt in the Arduino?

Did any of the input signals change while sending data over the serial?

3

In general printing in an ISR should not be done because serial print especially in the 1.0 version uses interrupts and you have them already disabled.