topic Re: Minimum Interrupt Latency in MQX Software Solutions

Minimum Interrupt Latency

stefangachter — Wed, 14 Mar 2012 18:25:55 GMT

We work with a MCF5232 based system running MQX and I would like to know the minimal necessary delay between two interrupt events, i.e. the minimum time to wait after quitting the ISR until a new interrupt can be triggered to enter the same ISR. I could not find any clear timing description and any advice would be appreciated.

Re: Minimum Interrupt Latency

c0170 — Wed, 14 Mar 2012 21:27:50 GMT

Hi stefangachter,

you are asking about interrupt rate not interrupt latency. There's not defined any time, it's code specific.

Regards,

MartinK

Re: Minimum Interrupt Latency

stefangachter — Wed, 14 Mar 2012 22:00:27 GMT

Thanks for the quick reply. So, this has to be implemented empirically and tested on each system individually?

Re: Minimum Interrupt Latency

MarkP_ — Thu, 15 Mar 2012 00:45:29 GMT

Hi,

One way to improve interrupt response time is to move vectors to RAM by defining in user_config.h:

#define MQX_ROM_VECTORS 0

And then installing interrupt routine as kernel-ISR.

Example where PE-generated code is changed to use own interrupt routine:

//DeviceDataPrv->SavedISRSettings_TUInterrupt.isrData = _int_get_isr_data(LDD_ivIndex_INT_FTM0);

//DeviceDataPrv->SavedISRSettings_TUInterrupt.isrFunction = _int_install_isr(LDD_ivIndex_INT_FTM0, PWM_Interrupt, DeviceDataPrv);

//Install own interrupt routine:

_int_install_kernel_isr(LDD_ivIndex_INT_FTM0, PWM_Interrupt_FAST)

This own interrupt routine is jumped directly from vector.

Note that MQX-services cannot be used from this own interrupt routine (not sure about this).

~Mark

Re: Minimum Interrupt Latency

DavidS — Thu, 15 Mar 2012 21:18:45 GMT

C:\Freescale\Freescale MQX 3.8\mqx\examples\benchmrk\timing\results\iar\twrk60n512\twrk60n512_intflash_release.html

System Parameters

Context Switch

4.30us

413.12us 1MHz

Service Interrupt and return to task

1.51us

145.40us 1MHz

System Timer/Tick Overhead

2.52us

242.40us 1MHz

Regards,

David

Re: Minimum Interrupt Latency

OldPeculier — Tue, 02 Jul 2013 15:34:03 GMT

Your reply is a little cryptic; What numbers refer to what?

I need to service my FlexCAN ISR in ~100us (the rate that fames can be received). Possibly can use _int_install_kernel_isr but I have never done a context switch in Freescsale, nor in c. Any examples for fast context switching?

Thanks very much!