Question on interrupt processing

[vhn]

Hi,
When the peripheral of a microcontroller is performing a job, if a interrupt arrives, at what instance will the interrupt be serviced ? How much latency should we consider?
For example,
Assme that a microcontroller is sending a byte on UART. After the first bit is transferred, an external interrupt arrives. Whether the interrupt will be serviced immediately or after the byte (remaining 7 bits) is transferred on UART?

Please suggest.

Thanks,
vhn

 

[sjerr4u]

According to me
in most of controllers there is independent UART unit so there are two cases
1) you are sending byte from normal routine ie not using UART interrupt
In this case sending of remaining bits will not stop (as UART is independent block) and interrupt will also be served immediately after executing current instruction and pushing PSW to stack.

2) if you are using uart interrupt
then if incoming interrupt will be served if it has higher priority. if incoming interrupt has lower priority then interrupt will not be served.

 

[dipal_z]

About Interrupt latency: Is is decided by your program and not by the micro controller, Microcontroller is always ready to serve the interrupts (it does have some overheads like finding vector, saving registers jumping to the ISR but they are constant) if interrupts are enabled.

If you have disabled interrupts or you are spending lot of time in an ISR (interrupts are automatically disabled when you enter and ISR). No interrupts will be services till they are re-enabled again, and that will determine your interrupt latency.