Interrupt Self-Nesting in CCES

Hi,

One possible way to avoid this situation is to use a lower-priority interrupt level to act as an intermediate interrupt.  For example, you could use software interrupt SFT2I for the actual work of your interrupt, then you could use SFT3I as an intermediate interrupt that simply raises SFT2I. 

So, here’s how it would look:

Timer Interrupt (handler):

                <do work>

                BIT SET IRPTL SFT3I;

<Return from interrupt>

SFT2I Interrupt (handler):

                <do actual work>

SFT3I Interrupt (app_IVT.asm hardware vector code):

.RETAIN_NAME ___int_SFT3I;           

___int_SFT3I:

                RTI (DB);                                // Just return…

                BIT SET IRPTL SFT2I;          // …setting SFT2I before you go.

                NOP; // 2nd delay slot

                NOP; // unused

.___int_SFT3I.end:

The SHARC hardware only clears the latch bit for the currently executing interrupt.  If you use SFT3I as the intermediate interrupt, then it will be possible for the Timer Interrupt to raise SFT3I whilst SFT2I is currently executing.  By doing this you should not lose an interrupt in the way that you describe.

We have encountered the same issue before on VDK (in VisualDSP) on SHARC, and we used the above SFT3I interrupt “trampoline” as a solution.

Please let us know if this helps.

Thanks

JamesH

Hi,

One possible way to avoid this situation is to use a lower-priority interrupt level to act as an intermediate interrupt.  For example, you could use software interrupt SFT2I for the actual work of your interrupt, then you could use SFT3I as an intermediate interrupt that simply raises SFT2I. 

So, here’s how it would look:

Timer Interrupt (handler):

                <do work>

                BIT SET IRPTL SFT3I;

<Return from interrupt>

SFT2I Interrupt (handler):

                <do actual work>

SFT3I Interrupt (app_IVT.asm hardware vector code):

.RETAIN_NAME ___int_SFT3I;           

___int_SFT3I:

                RTI (DB);                                // Just return…

                BIT SET IRPTL SFT2I;          // …setting SFT2I before you go.

                NOP; // 2nd delay slot

                NOP; // unused

.___int_SFT3I.end:

The SHARC hardware only clears the latch bit for the currently executing interrupt.  If you use SFT3I as the intermediate interrupt, then it will be possible for the Timer Interrupt to raise SFT3I whilst SFT2I is currently executing.  By doing this you should not lose an interrupt in the way that you describe.

We have encountered the same issue before on VDK (in VisualDSP) on SHARC, and we used the above SFT3I interrupt “trampoline” as a solution.

Please let us know if this helps.

Thanks

JamesH