I'm having problems with 8051 based ISRs. The problem occures when:
1- Interrupt A is being serviced. 2- Interrupt B occures and is serviced (in the middle of ISR A execution. 3- Sometimes ISR A fails to complete.
I'm using the C ISRs used in C51 without any register set defined ("using xx"). My understanding is that the ISRs should get entered and serviced mutually exclusive from one another without corrupting one another's stack. Is this not the case?
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The code is as follows:
===========Event A ISR============== void ISR_Sudav(void) interrupt 0 { // EA = 0; // Try dsiabling all IRQs. Doesn't help // EZUSB_IRQ_DISABLE(); // Try disabling all USB IRQs. doesn't help. SetupCommand(); // Service command
EZUSB_IRQ_CLEAR(); // Clear USB IRQ
INT2CLR = bmSUDAV; // Clear SUDAV IRQ
// EA = 1;
// EZUSB_IRQ_ENABLE(); } ==============Event B ISR ================= { void ISR_EP1(void) interrupt 0 { #ifdef USE_EP1_IRQ
// EZUSB_IRQ_DISABLE(); // Try disabling IRQs. Doesn't help!
// Do some stuff here
P_EPIRQ = 0x04; // Clear USB IRQ
// Clear USB IRQ EZUSB_IRQ_CLEAR(); // Clear USB IRQ
// EZUSB_IRQ_ENABLE();
}
The code posted appears to show two interrupt handlers attempting to service the same interrupt. Maybe it's some feature I'm not aware of, or maybe that isn't a copy and paste of the real code.
In addition to this, there's a brace imbalance and a possible attempt to call the same function from two interrupts of possibly different priority levels.
Might I suggest you reduce your code to the minimum that still shows the problem, then in the unlikely event you haven't found your mistake while doing so post the code using the tags intended for that purpose. Use copy and paste.
Thanks for your comments. The problem turned out to be something very simple. Solution:
In Event B ISR, P_EPIRQ = 0x04; which clears the IRQ has to be done after EZUSB_IRQ_CLEAR(); which is the global IRQ. Otherwise unwanted nesting occures.
The question that no one answered was whether the IRQs generated by C51 are nestable. From above, apparently they are not since nesting causes immediate failure.
This is not a general 8052 question. This is an add-on that is specific to your Chip. The general 8052 rules do not fully apply.