ARM712 IRQ masking

[philip1]

Posted on August 20, 2007 at 15:09

ARM712 IRQ masking

[philip1]

Posted on August 20, 2007 at 07:58

We are using an ARM712FR2T6 in a design and due to lack of thought in the hardware design we now find we need to modify pins of an output port during both normal and IRQ processing. I have masked the port modification at normal level using:

dVal = EIC->ICR; // Save ICR content

EIC->ICR &= ~0x0001; // Disable IRQ while changing Port Data

GPIO0->PD |= GPIO_PIN5; // Disable TX

GPIO0->PD &= ~GPIO_PIN6; // Enable RX

EIC->ICR = dVal; // Restore ICR content

but I find that the IRQ routine can still get in and upset the pin modification. If I put 8 'nop' instructions after the IRQ masking the problem seems to go away but I need to know if this is fixing it for good.

Is there a possibility of IRQ's still being active for some clock cycles after changing the ICR register? if so how many 'nops' do I need in order to be absolutely safe?

Thanks for any help

PhilipJ

[kleshov]

Posted on August 20, 2007 at 10:12

There was a discussion on this forum recently, you might find it interesting:

http://mcu.st.com/mcu/modules.php?mop=modload&name=Splatt_Forums&file=viewtopic&topic=5233&forum=17&start=0

[philip1]

Posted on August 20, 2007 at 15:09

Hi,

thanks for that, I failed to find the thread when I searched for anything related. It is exactly the problem I seem to be having and exactly the solution (8 nops = 2 instruction pipeline * 4xcpu clock).

It seems a shame that a discussion of such an esoteric aspect of the STR7xx processors does not prompt more of a response from the ST engineers themselves, but leaves us users to work out what is going on.

Oh well, it seems I have a solution and a reasonable explanation for why the solution should work

thanks again

PhilipJ