RE: nrf nus service cpu bandwidth usage as peripheral

MartinBL — Mon, 29 Jan 2018 13:30:13 GMT

Maybe this blog is of interest: Instrumenting with Segger SystemView.

You can find some information about the Softdevice's CPU usage here: Processor usage patterns and availability

RE: nrf nus service cpu bandwidth usage as peripheral

efiLabs — Sun, 28 Jan 2018 00:06:33 GMT

one of my application will need a certain amount of cpu bandwidth in order to fulfill it's functionality, like reading injector pulses and outputting them again, otherwise the engine stops ... most of it will be handled in high prio isrs (not as high as the nrf radio isrs) and some other isrs and some stuff will run at the main loop level

i have no real estimate of how much this will take and would not know in which measurement units i would express this

a previous product was based upon an ARM7TDMI-S cpu (lpc2148) and it ran fine ... had plenty of cpu left, based upon the main loop frequ.

since the unit is vehicle battery powered, i'm not worried about sleep or similar power saving options ... also my main loop test-setup is not setup to support sleeping at the moment

is there any cpu bandwidth measurement available to correlate a certain bit-rate in and out with no retries and cpu load % value ... and then how much does it degrade on a certain % of retries

since there is a practical max ble data rate for a single connection, or the whole radio, there should be a cpu on vs sleep % available for it ... one would think ???

it's hard to believe that i'm the only one asking for this ... yes there are apps where the cpu sleeps most of the time, but mine can't be the only one where the data throughput is the important factor and what's left over after all the data flow is handled

i suppose i could measure (estimate) it in a similar way by having a simple main loop freq measurement without ble connected and then connect and load the cpu with specified data in and out rates and see how the main loop frequ drops

any supporting thoughts are always highly appreciated

cheers Klaus

RE: nrf nus service cpu bandwidth usage as peripheral

MartinBL — Tue, 23 Jan 2018 12:09:45 GMT

Hi,

Calculating this is difficult as it depends on how much time the Softdevice has to spend dealing with packet loss, etc.

I think the most common way of doing this is to simply toggle a GPIO before and after entering sleep mode. Then measure this GPIO with a logic analyzer.