topic clocking LPTMR0 in Kinetis Microcontrollers

clocking LPTMR0

stefanomanca — Wed, 02 Jul 2014 07:05:49 GMT

Hi, I'm using kl14z64, when I clock the timer LPTMR0 by SIM_SCGC5 |= SIM_SCGC5_LPTMR_MASK; I observe that registers related to LPTMR0_XXX are initialized with not default value (see the pictures), in particular LPTMR0_CSR gets 0xC1 so when processor experts does NVIC_ISER |= NVIC_ISER_SETENA(0x10000000); starts a spurious interrupt.

Any idea?

Thank you

Re: clocking LPTMR0

bobpaddock — Wed, 02 Jul 2014 12:00:46 GMT

LPTMR0 registers are initialized only at Power On Reset. This is so they can maintain time across other resets.

The LPTMR is reset only on global Power On Reset (POR) or Low Voltage Detect

(LVD). When configuring the LPTMR registers, the CSR must be initially written with

the timer disabled, before configuring the PSR and CMR. Then, CSR[TIE] must be set as

the last step in the initialization. This ensures the LPTMR is configured correctly and the

LPTMR counter is reset to zero following a warm reset.
"

Re: clocking LPTMR0

stefanomanca — Wed, 02 Jul 2014 15:50:58 GMT

Hi Bob, I pray you to verify on your kinetis microcontroller if when you are at power-on LPTMR0_XXX registers are reset because in my case after power-on and after the SIM_SCGC5 |= SIM_SCGC5_LPTMR_MASK they are not zero. So something are going bad respect to the theory behavior. Anyway there is a bug in the processor expert initialization sequence. I hope in a freescale employ response.

Thank you.

Stefano M.

Re: clocking LPTMR0

Jorge_Gonzalez — Thu, 03 Jul 2014 13:53:00 GMT

Hello Stefano:

In fact I think the behavior you see is normal. To enter a debug session the MCU must be powered first (POR), and it runs enough time to configure LPTMR before you actually connect with the debugger. So the values you see are not those of Power-ON but the ones remaining after a reset by your tool (Multilink or similar).

To test this you can create a new empty project that just enables LPTMR with SIM_SCGC5 |= SIM_SCGC5_LPTMR_MASK and check the registers. You may need to close the first programming session and open another one for the Power-ON values to take effect.

Regards!,

Jorge Gonzalez

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Re: clocking LPTMR0

galadragos — Thu, 03 Jul 2014 18:44:00 GMT

Better do an actual power on, just to be sure.