How to store efficiently an array with over 100 000 byte elements and send it over BLE?

[Ina]

Hi!

I'm using nRF51DK with s110_nRF51_8.0.0 Soft Device and SDK_9.0.0. My application reads ADC with frequency 500Hz (2 bytes of data from one sensor each read), and twi with frequency 20Hz(6 bytes of data from another sensor each read) and sends each measurment over BLE instantly. Now i would like to modify it so that it stores measurments for 90 seconds and then sends all the data over BLE. I assume that i can not just make such a big array by simply writing in my code uint8_t arr[100800];, and i should, for example, use Persistant Storage Manager or some other method to store the data in flash memory. and here is my question: what method/ driver should i use to store my data so that it wont disturb reading ADC with high frequency (and so that i could write data into array after every read from sensor)? And how to send data over BLE after I read and store them? Should I use long-write or just split it by 20 bytes and send one after another (sending doesnt have to be done fast)?

Regards, Ina

[Wojtek]

It is not possible to store over 100kbytes in RAM (as the nrf51822 is limited to 16/32 kbytes), so simply writing uint8_t arr[100800]; wouldn't work indeed.

I don't think using flash memory would be fast enough to store these values, but if it even did, number of write cycles to flash memory is limited so I wouldn't recommend continuous writes to flash.

I suggest using external sram memory (ex. on SPI) to store data. To send this data the fastest way is to use notifications (20b data packets)

[Wojtek]

It's hard to say without seeing code of write to flash, but I assume that flash writes somehow block the CPU. SPI transactions to write flash take much more time than just simple data storage in internal RAM.