GPT driver for KINETIS K20

[SpaceCoaster]

Hi,

Attached are three patches which implement a version of the GPT driver for the Kinetis K20.

This driver is based on the PIT (Periodic Interval Timer) of the K20 and suffers from a fatal flaw! The polled mode can never work as the flag which signals when the interval has been completed is not set unless interrupts are enabled.

I am posting this GPT driver for the giggles and because the PIT register definitions and fields are useful.

Watch this space for a driver based on the FTM (Flexible Timer Module) devices.

Share and Enjoy,
Derek

[Giovanni]

You can do a polled interval just with a running counter, no need of flags. See the RT counter handling in the kernel.

Giovanni

[SpaceCoaster]

Giovanni,

Right, so I could use the PIT to handle the interrupts and just watch the current timer value count down in the polled mode.

I will give that a try.

Thanks,
Derek

[SpaceCoaster]

Never say never!

The attached patches implement a GPT driver based on the Kinetis PIT (Periodic Interrupt Timer) device. The driver supports all the modes, including the polled mode. A demo for the MCHCK-K20 board is included.

Previously, the counter was not running in debug mode, thus confusing testing. By enabling clocks when in debug mode the issues vanish.

I have tidied up the code a bit and used a pointer to the channels themselves to simplify access.

The underlying PIT device is a 32 bit counter which counts in SYSCLK units.

Cheers,
Derek

[SpaceCoaster]

The PIT timer on the KL25Z is very similar and it should be possible to move the driver to the LLD directory.

The KL25Z PIT has 2 channels and the K20 has 4.

The KL25Z also has a 64 bit mode which chains the timers together for what they call a lifetime mode.

2^64 cycles @ 100Mhz is around 6000 years!

[utzig]

2^64 cycles @ 100Mhz is around 6000 years!

Not sure if that's enough. Might need to run at a lower clock or use a prescaler!