using external flash MX25R1635FZUIL0 with nrf52 - having issues of writting and reading when multiple tasks are using the flash

[sara]

Hello, I am using MX25R1635FZUIL0 with nrf52  and my device is working with freertos.  I have three different tasks using/accessing  the flash functions but when i read back the data for all the 3 tasks i read some values as 0 and some as 0xFF and some correct values. But I need 100% correct data.my task 1 n 2 are sampling data at a speed of 256 Hz and then calling flash write function so when these two works together my error rate reduces but when i start the 3rd task which samples data at 16kHz i get only 1-2 % correct data for task 1 n 2 and almost all 0xFF for task 3. Can anyone please help me what should i do to get all the data correctly from flash 

[Susheel Nuguru]

I have never used this IC so i do not know the timing requirement it has with read sampling.  You should connect the IO pins to a logic analyzer to see if the third task is interfering with read transactions and changing the timings somehow. 

[sara]

thanks for ur reply Susheel, but if i run the task 3 alone having sampling rate of 16kHz it works properly but only when all 3 working issue arises. so will it interfere with read instructions? and apart from logic analyzer is there any other way i can find the issue?

[sara]

ok thanku Susheel , and yes i have checked with gsr n spo2 tasks working together and I used to get only 1-2% of error rate but when i introduce MIC task the issue arises. Meanwhile I will see if am able to manage logic analyzer or not as its a bit difficult for me to get it ryt now

[sara]

Hello Susheel, after trying to debug the issue I can confirm that when all 3 tasks working together when the data has been collected the value reads zero sometimes for this I found out that even if the value is written properly it reads wrong but when it is written n read immediately after that then it reads correct value but when later all the tasks have completed recording then when I read it gives wrong data sometimes so for this what can be the issue n how can I correct it?? Secondly I have a doubt can semaphore working be a problem ? I mean when it is released then there can be delay in taking it or vice-versa? I mean is there a way how can achieve tasks synchronous in such scenario?

[Susheel Nuguru]

Sara,

If the tasks are holding the semaphore for the whole transaction for that sensor (read/write/read_write) then you should not see any issues here. I think, the issue here is that the semaphore is being released too early and the other task is starting a read/write/read_write operation when the sensor has not still not finished completely from the previous operation. I would focus a bit more on the logic you have around releasing/locking this semaphore. Probably the sensor takes few us/ms more than what you think a read/write transaction needs from your driver? Try adding some timer delay (NOT busy loop) before and after every transaction (read/write/read_write) to fake extra time given for the transaction to complete and see if that helps. If it  does then you need to reconsider your semaphore release/locking logic

[sara]

Hello Susheel,

for delay u meant to use nrf_delay_ms(). ??

[Susheel Nuguru]

yes, busy delay would be easiest here just to give the external sensor time to complete the previous transaction. In any case comparing the timings of a transaction on the logic analyzer would have made your job easier to see why introduction of  MIC task  changes the states/timing of the data exchanged.