DMA for SPI master

[Juha Okkonen]

I'm reading AD-converter data usin nRF51822 SPI-Master. BLE-stack is active so I can't use interrupts with SPI. I get data every 2 ms. Sometimes Events are delayed so long that I get erroneous data from AD.

Is there some way to implement DMA for the SPI-Master, maybe using SPI-slave some way?

Juha Okkonen

[Bruce]

Hi Audun,

Could you please elaborate on how to synchronize radio activity with the AD reading to achieve 500Hz reading?

I'm in the same situation as Juha that the AD interupts every 2/4/8 milliseconds. And unfortunately, the AD conversion data has to be read out before the next interrupt comes.

Thanks, Bruce

[Audun]

Hi Bruce,

the radio notification functionality is a feature that triggers a software interrupt prior to, or after a radio interrupt (see https://devzone.nordicsemi.com/documentation/nrf51/5.0.0/html/group__t__s110___n_r_f___s_o_c___f_u_n_c_t_i_o_n_s.html#ga15378609daca09588e620b64555fc2e8). So if you need to perform stuff uninterrupted between radio events, or synchronize application tasks with radio activity, this is the best way.

In your case, you could enable the radio notifications to give you an interrupt when the radio interrupt is finished. When the radio event finishes, you can start a repeated timer with your AD interrupt frequency. If the bluetooth connection parameters doesnt crash with your AD frequency, you should be able to get a stable AD read frequency. Note that there will be some drift (depending on your clock source), and you would probably want to add some logic to keep your AD timer synchronized with the radio notifications.