RE: FreeRTOS : understanding vTaskDelay() import of Nordic SDK

Susheel Nuguru — Wed, 23 Mar 2022 09:33:39 GMT

I think this example was written when we incorrectly used configTICK_RATE_HZ as 1000 which made the developer assume that 1 tick = 1ms.

Later we realized that with RTC 1000 ticks cannot be produced so we change the tick rate to 1024 and yes that meant that each tick is around 0.9765ms.
So it is documentation bug to say that TASK_DELAY is 200ms and not 200 ticks.

[quote user=""]how do you guarantee vTaskDelay to work in ms time ? since this is contradicting the following article from freeRTOS : https://www.freertos.org/a00127.html[/quote]

portTICK_PERIOD_MS is practically useless with this prescalar. Like you have figured out this will give 0 and hence all your conversions using this will be incorrect. There will be no exact conversion of ms to ticks without using float, so I can suggest you use something like this

#define portMS_FROM_TICKS_CUSTOM(X)            ( (X * 1000) / configTICK_RATE_HZ )

#define portTICKS_FROM_MS(X)                   ( (X *configTICK_RATE_HZ) / 1000 )

This will be very inefficient the lower the X gets. If you want better accuracy with timings and conversions to be very accurate, then I do not think using RTC as main RTOS clock works for you. Then you need to use other high accuracy clocks.