I have a custom board that uses all UARTS, SPI and TWI. It's an ATUC3a0512 MCU development using AVR32 Studio.
I use the TWI only to interface with a real time clock chip. The USARTs handle serial communications to other devices and PC's.
I did my best to keep the interrupt functions short and sweet. However, I noticed if any interrupt happens during the TWI interrupt, the TWI interrupt locks up!
I tried to disable the USART during TWI scans by setting it's the idr bit. Once it set the ier bit after data had passed to the USART, the application locks up.
Question 1. Is there a maximum size for ISR's?
Question 2. Is it possible to change the size?
Question 3. Is a lower priority interrupt halted if triggered during a higher priority interrupt or delayed?