AM2434: Wanted: FreeRTOS example illustrating hardware interrupt and RTOS timer

Hi Johannes,

I experimented with xTimerCreateStatic(), and also with the ClockP API documented here: https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/08_02_00_31/exports/docs/api_guide_am243x/KERNEL_DPL_CLOCK_PAGE.html

It appears ClockP_construct() is a wrapper for xTimerCreateStatic(). I tried both APIs before and after the start of the scheduler. I'm able to see the system tick timer (DMTimer 8) is running. However, the R5F never arrives at the callback function for either API.

Johannes von Löwis said:

Also working examples that demonstrate how to use FreeRTOS timers and tasks together with interrupts would be welcome.

I don't see any simple examples of this in the SDK. I only see ClockP_construct() used in some of the networking examples:

<SDK>/examples/networking/enet_icssg_tas/enet_icssg_tas.c:1226:    status = ClockP_construct(&gEnetTas.tickTimerObj, &clkParams);
<SDK>/examples/networking/enet_layer2_cpsw/V0/l2_cpsw_dataflow.c:97:    status = ClockP_construct(&gEnetApp.tickTimerObj, &clkParams);
<SDK>/examples/networking/enet_layer2_cpsw_switch/V0/l2_cpsw_dataflow.c:97:    status = ClockP_construct(&gEnetApp.tickTimerObj, &clkParams);
<SDK>/examples/networking/enet_layer2_icssg/enet_layer2_icssg.c:1277:    status = ClockP_construct(&gEnetMp.tickTimerObj, &clkParams);
<SDK>/examples/networking/enet_layer2_timesync/V0/timesync_dataflow.c:97:    status = ClockP_construct(&gEnetApp.tickTimerObj, &clkParams);
<SDK>/examples/networking/enet_layer2_timesync/V1/timesync_dataflow.c:97:    status = ClockP_construct(&gEnetApp.tickTimerObj, &clkParams);

I'll follow up with the SW dev team on this, and keep you posted on what I find.

I was able to use Sysconfig and TimerP to configure another timer independent from the system timer. Please see docs for TimerP here: https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/08_02_00_31/exports/docs/api_guide_am243x/KERNEL_DPL_TIMER_PAGE.html

To add a timer, open your .syscfg file, click on "TIMER", and read through the instructions. Note there is a mistake in the instructions: TimerP_start(&gTimerHwiObj[CONFIG_TIMER0] should be TimerP_start(gTimerBaseAddr[CONFIG_TIMER0])

You could take this approach instead of using xTimerCreateStatic() / ClockP():

• Use TimerP API
  
• Post semaphore in timer ISR
• Trigger task to execute your periodic code when semaphore is posted

The task code would be interruptible by the ADC ISR.

Regards,
Frank

Hi Frank,

thank you for taking the time looking into this.

I used Sysconfig to put my millisecond code as timer callback for TIMER0. There I stumbled across the problem that the callback was not interruptable by the 16 kHz ADC interrupt.

My desired configuration would consist of

• The RTOS maintask which, after some initialization enters a while(1) loop where non-timecritical functions are called repeatedly. This maintask should be interruptable by the millisecond routine and the 16 kHz interrupt.
• A routine (maybe a second RTOS task?) which should be called every millisecond containing stuff that should easily be accomplished within one millisecond. This routine should be able to interrupt the RTOS maintask and be interruptable by the 16 kHz interrupt.
• A 16 kHz interrupt which should not be delayed by the millisecond routine nor the RTOS maintask.

The examples that I have found so far communicate with RTOS main task using a semaphore.

So far I have not been able to get a second RTOS task (executed every millisecond) working.

Best regards,

Johannes

Hi Johannes,

Johannes von Löwis said:

I used Sysconfig to put my millisecond code as timer callback for TIMER0. There I stumbled across the problem that the callback was not interruptable by the 16 kHz ADC interrupt.

Understood, that's why I suggested placing your msec code in another task which is triggered by a DM Timer. Ideally, you'd be able to setup a ClockP based on the system tick DM Timer to trigger to 1 msec task.

Until we hear back from the SW Dev team on why ClockP (and xTimerCreateStatic()) isn't working, can you try using a DMTimer for the 1 msec task trigger? 

Johannes von Löwis said:

The examples that I have found so far communicate with RTOS main task using a semaphore.

I assume you're referring to this example: https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/08_02_00_31/exports/docs/api_guide_am243x/EXAMPLES_KERNEL_FREERTOS_TASK_SWITCH.html

This code configures three tasks, but it could modified to setup your main task and your 1 msec task. The 1 msec task would have higher priority than the main task. If you can get this working, then it should be a simple matter of "plugging in" ClockP when we get that working.

Johannes von Löwis said:

A 16 kHz interrupt which should not be delayed by the millisecond routine nor the RTOS maintask.

Because nested interrupts are disabled, the system tick ISR (and a separate 1 msec DM Timer) can delay your ADC ISR (e.g. system tick ISR is active when ADC ISR occurs), and also be delayed by the ADC ISR (e.g. ADC ISR is active when system tick ISR occurs). If the timer ISR cycles are kept to a minimum, this might be acceptable, but it depends on your system requirements.

I'll keep you posted on what I hear back from the SW Dev team.

Regards,
Frank

Hi Frank,

thank you for your response. Meanwhile, I have found some issues in the legacy code parts that I had quickly added to my test project. I assume, due to those issues RTOS structures got corrupted and I saw strange behaviour.

My current solution involves two tasks: a one "millisecond task", that is triggered by my 16 kHz interrupt (every millisecond) and one "main task" that is triggered by the millisecond task, both using semaphores. With this solution I was able to get about 1 us jitter of the entry into 16 kHz interrupt.

When I tried to trigger the "millisecond task" using a timer interrupt, the jitter of the entry into 16 kHz interrupt was about 2 us.

Best regards,

Johannes

Hi Johannes,

I'm glad you were able to make progress. Is the jitter acceptable for your application?

Regards,
Frank

Hi Frank,

thank you for the links to the RTOS important guidelines. To me the statements in

https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/08_02_00_31/exports/docs/api_guide_am243x/KERNEL_FREERTOS_PAGE.html#autotoc_md324

("nested interrupts is disabled") and

https://software-dl.ti.com/mcu-plus-sdk/esd/AM243X/08_02_00_31/exports/docs/api_guide_am243x/KERNEL_FREERTOS_IMPORTANT_GUIDELINES_PAGE.html#autotoc_md339

("IRQs are then enabled, i.e nested interrupts are enabled") seem contradictory.

I'm confused.

Best regards,

Johannes