Accurate pwm in CC2540

Albert Skog

Other Parts Discussed in Thread: CC2540

Hello! I am working with SimpleBLEPeripheral, trying to interface a servo motor by sending 1-2ms pulses every 20ms using osal events and timer 1. Every 20ms an event is triggered (this timing is not critical), and timer 1 is started for, lets say, 1.5ms (critical). Observing this signal it turns out the 1.5ms pulse will some times be up to 3ms due to some halts within the stack which I cannot control. What would be the correct way to implement a time critical output?

over 13 years ago

0 Igor Sherer over 13 years ago

Guru 31280 points

If I understand this right, the 1.5mS pulse generated by timer1 and shouldn't be affected by

stack if. Just check in the stack (probably application) that timer1 isn't used to operate other

devices, such as buzzer, or something.

0 Albert Skog over 13 years ago in reply to Igor Sherer

TI__Prodigy 300 points

Correct, I am using the channel 1 output of timer 1 (P0_3) on the usb dongle from the mini development kit.

As far as I have been told the stack halts the CPU when the radio is on, so if a connection event occurs during my pulse, the timer will be momentarily halted and the pulse will be longer.

I found this out by digging down through the initialization calls of the example - if i comment out the call to GAP_ParamsInit() in gap.c, the pwm works fine.

0 Igor Sherer over 13 years ago in reply to Albert Skog

Guru 31280 points

Hi Albert,

Timers (T1, T3 and T4) are autonomous units, so unless the device is in power mode PM2 or PM3

(cc253x/4x User's Guide, section 4.1) timers should keep on running as configured regardless of

CPU and/or Radio activity.

May be what you see there is cc2540 switching to PM2 or PM3 and timers are halted.

0 Albert Skog over 13 years ago in reply to Igor Sherer

TI__Prodigy 300 points

Sorry, I was editing my last post while you answered, let me say again that: I found this out by digging down through the initialization calls of the example - if i comment out the call to GAP_ParamsInit() in gap.c, the pwm works fine.

Igor Sherer said:

Timers (T1, T3 and T4) are autonomous units, so unless the device is in power mode PM2 or PM3

(cc253x/4x User's Guide, section 4.1) timers should keep on working as configured regardless of

CPU and Radio activity.

May be what you see there is cc2540 switching to PM2 or PM3 and timers are halted.

Yes, PM2 or PM3 is what i believe is happening. I just got an idea, perhaps the code is expecting a sleep crystal which the usb dongle does not have, SimpleBLEPeripheral was not exactly written for it..

0 Igor Sherer over 13 years ago in reply to Albert Skog

Guru 31280 points

Well, unfortunately I'm not familiar with BLE, nor with CC254x based EMs, dongles etc.

So I can't tell you what is exactly happening there :)

0 Albert Skog over 13 years ago in reply to Igor Sherer

TI__Prodigy 300 points

Igor Sherer said:

Well, unfortunately I'm not familiar with BLE, nor with CC254x based EMs, dongles etc.

So I can't tell you what is exactly happening there :)

Thanks anyway! I was debugging this for quite some time until we discovered it is not even possible to get a simple square wave from the timer output without disabling parts of the stack. So yes, it's a rather specific BLE/cc254x issue i would say..