TI RTOS "zero latency" interrupt

Enrico Pietrantozzi

Other Parts Discussed in Thread: SYSBIOS

Hi, i'm evalueting TI RTOS on C28069stick for next platform on my project.

Interrupt latency and timings are mandatory for my devices.

I have an interrupt on the return to zero of the COUNTER of PWM 1 (PRD) running at 45 kHz. The execution of the interrupt is configured with the GUI. In the interrupt i only toggle a led in order to measure how much time lasts from the interrupt (down fall of the pwm and the toggle of led). Everythning seems to work fine, but I measure 10 us for the first istruction of the interrupt. I think something wrong in my settings.

Can you help me? Attached screnshot

PS: Hwi TIMER is disabled so is not running

over 9 years ago

0 judahvang over 9 years ago

TI__Mastermind 32475 points

Hi,

Sorry, can you be more clear on what you think is wrong? I don't see anything wrong with your SYSBIOS configuration.

Judah

0 CM2015 over 9 years ago

Expert 1060 points

Can you clarify what time you are measuring that is 10uS?
Also:
Is your device sleeping and being woken up by the interrupt? If so, you can expect some significant amount of delay before entering the ISR. If you disable the device from going to a sleep or low power mode it should reduce the latency. Another thing to note about zero latency interrupts is they do not use the rtos dispatcher and as such can NOT call rtos api functions (like posting a semaphore, blocking, queueing etc).

0 Enrico Pietrantozzi over 9 years ago in reply to CM2015

Prodigy 140 points

Thank you for the answer,

I'm measuring the time between the down fall of the PWM pin (generating an interrupt) and the first execution of code inside the interrupt (GPIO toggle).

In my case 10 us to execute the first interrupt correspond to 900 cycle clock, but it's supposed to be much less i think.

In effect i don't have an IDLE running, so it could be sleeping. I investigate this issue and reply.

Thanks

0 Enrico Pietrantozzi over 9 years ago in reply to Enrico Pietrantozzi

Prodigy 140 points

With an IDLE running, nothing different. CPU is not in sleep or low power mode.
Using same code but with the interrupt Hwi managed by SYS, the latency seems to be 1us (according with the paper i've got).
Something must be wrong...
Any ideas?
Thanks

0 Enrico Pietrantozzi over 9 years ago in reply to Enrico Pietrantozzi

Prodigy 140 points

Fixed! Some line were missing

Hwi_plug(PWM3_1, (Hwi_PlugFuncPtr)gpioToggle);
Hwi_enableInterrupt(PWM3_1); //Need to explictly enable 0-lat

Now the problem remain the jitter that goes from typical 350 ns to occasional 8 us

0 judahvang over 9 years ago in reply to Enrico Pietrantozzi

TI__Mastermind 32475 points

Are there any other interrupts in your system? Could you try disabling them to see what happens?

0 Enrico Pietrantozzi over 9 years ago in reply to judahvang

Prodigy 140 points

No, no other interrupt is running.

0 judahvang over 9 years ago in reply to Enrico Pietrantozzi

TI__Mastermind 32475 points

Are you disabling interrupts in your code somewhere for a long time? Or is your ISR taking too long?

I know SYSBIOS does not disable interrupts in the order of 8us long (that's like 700-800 clock cycles?)

Judah

0 Enrico Pietrantozzi over 9 years ago in reply to judahvang

Prodigy 140 points

I've attached the project. I'm no stopping the interrupt.

Exploring the functionality of the SYSBIOS i've activated a serial communication and a timer function. Everything's working fine, but i see those big latency on the interrupt (only gpio toggle, so is not too long).

For my application this timing is really mandatory, if not fixed i must discard TI RTOS and continue using while(1)... :)

6232.controlSTICK_PiccoloF28069.zip

0 judahvang over 9 years ago in reply to Enrico Pietrantozzi

TI__Mastermind 32475 points

Okay, I took your project and looked at it. I do see some things that need to be correct!

1. You have: ti_sysbios_family_c28_Hwi.zeroLatencyIERMask = 48;
But this means you have designated PIE groups 7 and 8 as zero latency interrupts.

What you really want to do is designate PIE group 3 as zero latency which is where interrupt 48 resides:
ti_sysbios_family_c28_Hwi.zeroLatencyIERMask = 0x0004;

2. I also do see that the SYSBIOS default Timer has not been disabled. If you need clock services, you will need this enabled,
However, you should try disabling this to make sure all other interrupt are disabled.

var BIOS = xdc.useModule('ti.sysbios.BIOS');
BIOS.clockEnabled = false;

Judah

0 Enrico Pietrantozzi over 9 years ago in reply to judahvang

Prodigy 140 points

Thank you! Now it's working!

I've put the interrupt number instead of group mask.

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TI RTOS "zero latency" interrupt