Sending 30000 bytes to Android Phone every 30 seconds while UART is receiving data every 40ms

[kian79]

Hi all,

I am working on a project where the requirement is a sensor collecting data and sending to the NRF52832 via UART. Every 40ms, the NRF52832 will receive 40 bytes of data. I need to store 30 seconds worth of data in RAM (about 30000 bytes) then transfer everything via BLE to a mobile app. While it is transferring this data, UART still needs to work and collect 40 bytes every 40ms.

What I have done previously was to send the data out via BLE immediately at every 40ms and this works fine. However, the app developer ask that I only send the data over only every 30s. I am now stuck with how I can collect 30000 bytes first and still have UART working while doing the BLE transfer. I don't really have an idea of what kind of modifications I will need to make to the BLE_UART example code.

Anyone can help? Thanks in advance.

[MartinBL]

Hi,

It sounds like using your UART with EasyDMA combined with a timer, a counter, and some PPI channels could solve your problem. In short, you can set up a timer to trigger an event every 40ms and connect this via PPI to a transfer task in your UART. You can then use EasyDMA and let the UART transfer data directly to a buffer in RAM. Use the counter to count the number of transfers and fire an interrupt when you have enough data to send. You can do all these things completely autonomously, without using the CPU and hence, not block any BLE transfers. After 30k samples, when it is time to transfer your data, the counter interrupt triggers, you swap your buffer to a secondary one and then start transferring your first buffer. 

[kian79]

Thanks MartinBL!

I think I found an example which is somewhat similar to what you had described, except this uses TWI:

https://github.com/Martinsbl/nrf5-mpu-examples/tree/master/nrf52-mpu-easydma-using-timers-and-drivers

I should be able to use these codes as a starting point. On a side note, having a secondary buffer would mean having to reserve 60k of RAM. Is this even possible? There is only 64k of RAM on the nrf52832.

[MartinBL]

Good point. S132 v5.1 requires 4.6kB of RAM alone, so 60k of buffers is out of the question.