Best way to do high frequency writes to SPI - using ticker?

RE: Best way to do high frequency writes to SPI - using ticker?

dmf3030 — Fri, 24 Jul 2015 17:28:18 GMT

The actual LEDupdate function that the ticker is pointing to is very quick, just moving some data around in an array. The SPI write where I actually push that data to a strip of LEDs happens in the LEDs.update(); call which is in the main loop. Basically the ticker updates the LED data then sets a flag so that the next time you hit the main loop the function to push that data to the SPI is called.

I haven't had a chance to remove the SPI writes that are in the main loop, but I will do that now to see if I can still get a hardfault there. I also need to figure out why adding a characteristic to my service causes the a fault where the code was stable before. I'll report back with anything I find.

RE: Best way to do high frequency writes to SPI - using ticker?

Hung Bui — Fri, 24 Jul 2015 14:20:30 GMT

@dmf3030: How long did it take in your ticker call back (LEDupdate) ? If it's a long process, you may consider doing it in the main loop. The ticker call back only set a flag.

Have you tried to remove the SPI code in the call back and check if hardfault still occurs ?

RE: Best way to do high frequency writes to SPI - using ticker?

dmf3030 — Fri, 24 Jul 2015 12:06:30 GMT

Forgot to answer your final question, my connection interval is the default setup for mbed

 static const unsigned GAP_ADV_PARAMS_INTERVAL_MIN        = 0x0020; // 40ms
static const unsigned GAP_ADV_PARAMS_INTERVAL_MIN_NONCON = 0x00A0; // 200ms
static const unsigned GAP_ADV_PARAMS_INTERVAL_MAX        = 0x4000; // 20480ms
static const unsigned GAP_ADV_PARAMS_TIMEOUT_MAX         = 0x3FFF; // 163830ms

RE: Best way to do high frequency writes to SPI - using ticker?

dmf3030 — Fri, 24 Jul 2015 11:37:28 GMT

Sorry I understand the mbed API is its own world, I have posted this to the mbed forum but I've found the nordic forum to be much more responsive and I've found good info here so I decided to give it a shot. I will add the actual code I'm using to the main question for clarity and I will also try your two suggestions of just doing a delay instead of SPI and of doing nothing in the onDataWritten function.

I guess the primary question still persists, is this the correct way to approach writing to the SPI repeatedly at a relatively short interval, (8-10ms at the shortest)?

RE: Best way to do high frequency writes to SPI - using ticker?

Hung Bui — Fri, 24 Jul 2015 09:34:16 GMT

@dmf3030: We don't have much experience with mbed so I would suggest you to also create a thread on mbed forum to seek for help.

It sounds strange to me that a short interval tiker ( I assume you were using a timer to do the tick) would cause a hardfault.

What if you try:

don't do any thing SPI related in the ticker handler, but just a simple delay in the ticker handler?
don't do anything in onDataWrittenCallback()

What was your short ticker interval and what was the long one ? Also what was your connection interval ?