nrf52 PPI+EasyDMA using timer and SPI

[Vishnu Pradeep]

Hi,

I am using nrf52832 for my application. The application share same SPI module for two sensors(with sensors are selected using two chip select pins). Is it possible to implement PPI channel between a timer and this SPI module so that I can collect data from both the sensors every 1ms? I would like to collect the SPI data using EasyDMA and send these data through BLE every 50ms. how can it be achieved with the help of PPI and EasyDMA?

[Wojtek]

Yes, it is possible. may be something like:

1. Setup spi, transmission buffers, timers etc
2. Start 1st SPI transmission (either by timer PPI or manually by software - every 1ms)
3. When transmission end, toggle CS pins by gpiote (triggered by spi end ppi), start timer
4. when timer end, start second spi transmission (buffer pointer automatically incremented by array list).
5. Data may be moved somewhere else, or just long arraylist may be used.
6. goto 2?

I may have skipped something, but in general, that should be doable. It also can be achieved quite easily completely without using ppi, timers etc - just by software app_timer, as 1ms is not that high freq.

About sending it by BLE every 50ms... I would just use app_timer too for that.

[Wojtek]

Ok, I'll try to exaplain it differently:

EasyDma gives You possibility to transfer data, ex. 20 bytes without using interrupts between them. You just start transmission, and it goes 20bytes.

PPI can be used to ex. set hardware timer, it triggers PPI periodically, PPI triggers SPI START task.

When SPI START is triggered, 20bytes (MAXCNT) are transmitted (thanks to EasyDMA) without using interrupts.

The problem is, you want something like: SPI start -> transmit 75 bytes -> toggle pins etc -> transmit 5 bytes. It is not possible to change from 75 to 5 bytes without CPU intervention (ppis can only trigger transmission starts, toggling pins etc), that is why You need one interrupt there anyway.