MPC5xxxのトピックHow to use the Frequency Meter in the MPC5645S?

How to use the Frequency Meter in the MPC5645S?

janos_murai — Fri, 05 Jan 2018 15:05:25 GMT

Hello all,

I would like to measure the frequency of the SXOSC. For this, I would like to use the CMU (Clock Monitor Unit).

My problem is that I cannot write to the appropriate registers.

- The processor is in DRUN mode.

- There is no active write protection for the CMU registers.

- The system clock is the FXOSC.

- FXOSC, SXOSC are enabled.

Any idea what could cause the problem?

Thank you!

János Murai

Re: How to use the Frequency Meter in the MPC5645S?

davidtosenovjan — Fri, 05 Jan 2018 17:09:53 GMT

Are you executing in supervisor mode?

Re: How to use the Frequency Meter in the MPC5645S?

janos_murai — Mon, 08 Jan 2018 08:57:14 GMT

Yes, the MCU is in supervisor mode (the MSR.PR bit is zero).

In RUN0 mode: I can't modify the registers, always the reset values are present.

In DRUN mode: If I write anything to the CMU.CSR register it becomes zero.

János

Re: How to use the Frequency Meter in the MPC5645S?

davidtosenovjan — Mon, 08 Jan 2018 12:18:36 GMT

What is your compiler? Have you tried to see the register over memory dump window?

Re: How to use the Frequency Meter in the MPC5645S?

janos_murai — Mon, 08 Jan 2018 13:02:45 GMT

The compiler:

The memory dump:

These are the values that I can read back in C. These are the reset values, as noted in the RM.

Although, there might be something with the debugger, because if I press step over, the values change kind of randomly, while I can see in the disassembly that non register writing instructions are executing...

Re: How to use the Frequency Meter in the MPC5645S?

davidtosenovjan — Wed, 10 Jan 2018 07:57:45 GMT

Currently we don't have any working evaluation board with MPC5645S. We have ordered one and when it arrives (probably next week) I will try it. For now I am short of ideas. Do you see this behavior only with CMU registers?

Re: How to use the Frequency Meter in the MPC5645S?

janos_murai — Wed, 10 Jan 2018 08:45:03 GMT

Thank you David!

All the other registers that I use can be modified without any problem. So I don't face this behavior anywhere else...

Re: How to use the Frequency Meter in the MPC5645S?

janos_murai — Tue, 30 Jan 2018 14:29:03 GMT

davidtosenovjan ,

could you figure out something?

I just realized that I have a very similar issue with the MPU (Memory Protection Unit). All the MPU registers are writable except the CESR.VLD. So I have a feeling that it should be something with the privileges...