SmartFusion2 Port: Timer

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1

Dear List,

In an effort to port RIOT to SmartFusion2 (goto BACKGROUND at the bottom for interest), we’ve hit a small stumbling block. The dedicated hardware timer is extremely basic and does not have any CCP (capture/compare) channels. It’s is a simple down counter with an overflow interrupt.

This seems to be a bit of a show stopper in regard to periph/timer.h and xtimer: int timer_set_absolute(tim_t dev, int channel, unsigned int value);

We’ve tried to keep the FPGA realm out of the equation as an initial strategy, since it could contain anything and we need to devise a structure that will fit with RIOT for the FPGA contents. That said we could implement a timer core with the necessary functionality and use it for periph/timer.h and xtimer …

Would that be the best or are we overlooking another option?

BACKGROUND: SF2 is a device that interfaces low power FPGA fabric with a hard-wired CortexM3. It has a few basic (optional) peripherals, but the FPGA practically opens up endless options. Currently we have two basic examples (default, hello-word) running on the SF2-STARTER-KIT board, with a M2S010 SF2 device. We reckon this is an exiting development - it seems that FPGAs are currently not really featuring in this space - but offer unique field upgrading of hardware subsystems e.g. security blocks or edge data processing algorithms.

Kind Regards, Gideon

2

Hi Gideon,

Dear List,

In an effort to port RIOT to SmartFusion2 (goto BACKGROUND at the bottom for interest), we've hit a small stumbling block. The dedicated hardware timer is extremely basic and does not have any CCP (capture/compare) channels. It's is a simple down counter with an overflow interrupt.

Can the start or reload value be set, and the current counter value be read?

If yes, this sounds much like the Cortex-M systick timer. It should be possible to emulate a one-CCP counting timer.

When no callback is set, now() is "MAX_VALUE - current_value", and the overflow interrupt is ignored.

If a callback is set, the timer gets (re-)set with the timeout as start value, and the callback is executed on overflow, where the start value then gets reset to MAX_VALUE. Also, the time when the callback gets configured is stored somewhere and then incorporated into now().

This will be difficult to implement without losing a tick here and there, but might be acceptable.

Kaspar