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Fast External Interrupt

Kieran Dobbyn

I need to implement a fast external interrupt with a C167CR micro on a Phytec phyCORE-167 board.
At the moment, I have my external interrupt signal connected to pin P2.15
and program it as follows:

      EXICON = 0x4000;    // Set Ext Trigger Interrupt for rising edge
response
      CC15IC = 0x4c;              // Enables Ext Trigger Interrupt, Global
Level = Lowest, Priority Level = Medium
      IEN = 1 ;                         // Enable Interrupts

When an interrupt occurs, I then want to set another port pin which is done
within the interrupt handler, as shown below:
     void Boxcar_irq (void) interrupt CC15INT = 31
     {
         CC15IC = 0x0;                // Disable further interrupts
         EXTTRIG_GATE = 1;     // Sets pin P2.1 High

         return;
     }
This arrangment works, i.e. the interrupt is trapped and the port pin set
low, but the response time I am getting is 5.4uS.
I have measured this as the time from the rising edge of the external
trigger signal to the rising edge of P2.1.
I do not have any other interrupts running or enabled so I don't set this
interrupt to highest priority.

Can you suggest a way that I can improve the interrupt response time.
I would like to get below 1uS if possible.

My application program is approx 20kB in size and runs from external RAM using.

Any ideas?

Best Regards,
Kieran Dobbyn

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  • 0

    Hi Kieran,

    Probably the fastest response you can get is when the fast external interrupt triggers a PEC transfer to the output port data register. But it is not possible to set individual port bits this way.
    To get the fastest possible response with the interrupt handler you have to make sure that the instruction that sets the output port is as close to the entry point of the interrupt handler as possible. You can always put it right in the interrupt vector table, and that would involve assembler, of course. The other issue is program execution speed from external RAM. If the external bus interface is not in 16-bit demultiplexed mode with no extra delays, than the interrupt handler will run faster from on-chip RAM.
    By the way, 5.4uS sounds like ages. Are you sure you chose the fastest possible CPU clock frequency?

    Regards,
    - Mike

Reply
  • 0

    Hi Kieran,

    Probably the fastest response you can get is when the fast external interrupt triggers a PEC transfer to the output port data register. But it is not possible to set individual port bits this way.
    To get the fastest possible response with the interrupt handler you have to make sure that the instruction that sets the output port is as close to the entry point of the interrupt handler as possible. You can always put it right in the interrupt vector table, and that would involve assembler, of course. The other issue is program execution speed from external RAM. If the external bus interface is not in 16-bit demultiplexed mode with no extra delays, than the interrupt handler will run faster from on-chip RAM.
    By the way, 5.4uS sounds like ages. Are you sure you chose the fastest possible CPU clock frequency?

    Regards,
    - Mike

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