Question about INT instruction

Hi,

Just a query for microprocessor. When we are calling software INT instruction(like int 21), does this lock out the IRQ request from the hardware?

Thanks

Re: INT REquest

I think that making a function call to an ISR (Interrupt service routine) doesn't mask the servicing of an IRQ during its execution, except when the same function includes interrupt disable or mask instructions: therefore you have to design the function to be re-entrant (nested multiple calls of the function during its execution).
Anyway check in the programmer's guide of the processor how the IRQ function calls are managed.

Regards

Mowgli

Re: INT REquest

THanks! But what if the INT you are calling is also connected to the IRQ of the Programmable Interrupt controller..

For example, If I am trying to write an interrupt service routine for RTC(real time clock, which is connected to IRQ 7),

when this interrupt is being called, from the processor using INT xx(to trigger the Interrupt service routine I have written for it), would I still be able to use/ access other hardwares which is also tied with to the IRQ eg mouse(at a lower Interrupt piority) while I am in the interrupt service routine itself.

Would calling INT in this manner, stop the other IRQ from responding while I am in this interrupt service routine?

Thanks

Re: INT REquest

As I wrote in my past reply, making a function call to an interrupt servicing routine ( = calling the function in the SW when the Interrupt line has not been asserted by the associated HW event) generally does not disable or mask the associated HW interrupt.
This is not true if the function (or the SW before the call) executes instructions that disable or mask the IRQ (every processor has internal registers to control enabling/disabling/masking of its HW IRQ lines by SW).
Once made this premise you should be aware that to perform a function call to IRQ routine you shall design the function as reentrant, taking account of the possibility that the IRQ triggers its execution while it was already running due to previous explicit call.

Regards
Mowgli