Dynamic control of the PWM output using HET when running in user task

Shing Lee

Other Parts Discussed in Thread: HALCOGEN

I tested the HET/PWM driver generated by Halcogen on the RM48 USB development stick and it works fine when the hetInit(), pwmStart() and pwmStop() are called from the main() function. However, when these functions are moved and executed within one of the tasks (I am using FreeRTOS), then the PWM operation does not work anymore. As the hetInit(), pwmStart() and pwmStop() all require access to the HET RAM, I wonder if it is something to do with the MPU. I disabled the MPU via Halcogen, but it still doesn't work. Any idea why?

Development platform: RM48 USB development stick

Halcogen: version 3.06.00

CCS version 5.3.0.00090

over 12 years ago

0 Anthony F. Seely over 12 years ago

TI__Guru 69070 points

Some of the N2HET control registers are writeable only in a privileged mode.

This check is performed by the N2HET itself, not the MPU. So disabling the MPU won't disable this check.

You could probably move hetInit() back to your main() function and make it work.

Or you could make sure that the FreeRTOS task you want to call these functions from has privilege set.

See: http://e2e.ti.com/support/microcontrollers/hercules/f/312/p/265289/929223.aspx#929223 for an example of how to accomplish the latter.

0 Shing Lee over 12 years ago in reply to Anthony F. Seely

Intellectual 545 points

Thanks for your prompt reply. The suggested privilege setting in TaskCreate works. Would you also advise if it can be done in Timer callback function too? Thanks

0 Anthony F. Seely over 12 years ago in reply to Shing Lee

TI__Guru 69070 points

Hi Shing,

Super.

I believe the Timer callback is executed in IRQ mode, but it might be different depending on how you get from the IRQ vector to the callback routine.

Basically any mode except for user mode has privilege; so from any mode that is not user mode you can write those protected HET registers.

You confirm the CPU mode by checking the CPSR register when you are halted inside the timer callback.

User mode is M[4:0] = b10000; IRQ mode is M[4:0] = b10010; etc...

Arm-based microcontrollers

Arm-based microcontrollers forum

Dynamic control of the PWM output using HET when running in user task