TMS320F28386S: F2838xS - ADC interleaving

Hello Mauro,

The ePWM module has two ADC event triggers for each module - ADCSOCA and ADCSOCB. Each of these can be triggered at a different counter compare, so you could have SOCA trigger at the beginning of the period and SOCB halfway through the period, for example. You don't need to use up two different ePWMs to achieve this.

Best regards,
Ibukun

Thanks for the follow up. What you have described would work if I would interleave 2 ADC.

If I want to interleave 3-4? 

Should I use 2 timers? (one for each 2 ADC?)

Can I sync the two timers so that I can trigger the 4 ADC with the right trigger (keeping the sample period the same)?

Last resources would be to check the assembly code lines that gets executed by starting the first timer and the second.

By checking it I can anticipate/delay the counter to load on the timers. 

Thanks, 

Mauro 

Hello Mauro,

Apologies for the delay responding as I was out of office.

This depends on what you're trying to achieve. If you want to trigger multiple ADCs on the same event, you don't need to use multiple PWMs/timers. The same ADCSOCA/B signal can trigger multiple ADCs at once. So the number of SOCA/B trigger signals you need is determined by how many different points in time you want to start an ADC conversion - for a particular trigger, you could trigger as many SOCs as you want to.

If you do need to space them out at different time points, then yes you would need to use more than one ePWM. You can synchronize the PWM periods and configure them such that you can trigger your ADC SOCs at the exact cycle in the period you wish to.

Best regards,
Ibukun

Thanks for the follow up.

The scenario would be the second one:

If you do need to space them out at different time points, then yes you would need to use more than one ePWM. You can synchronize the PWM periods and configure them such that you can trigger your ADC SOCs at the exact cycle in the period you wish to.

Do you have an example/recommendation to sync two timers, so that the sampling period of the 4 ADC out the two timers, would be equally distanced.

Thanks,

Mauro

Hi Mauro,

Yes, you can have several EPWM's running at the same time (synced) to trigger ADCSOCs equally distanced in time. 

Have you also had a chance to look at some of our ADC SOC examples in C2000Ware to see if they can be leveraged for your requirements? They are located at {C2000Ware}\driverlib\f2838x\examples\c28x\adc and are a great reference and starting point for this.

Best Regards,

Allison

Hello Allison,

thanks for the follow up. 

from a look to the examples, the interleaved one is interleaving 2 ADC, thus with a timer could be done. 

Using more than 2 ADC the challenge would remain.

You have mentioned that I could sync more timers.

I have taken a look to the timers examples, and there is no reference on how to sync those. 

Can you point this out?

By MSPM0 I can use the shadow register of each timer. I can set the timers to load the shadow register with a common trigger. I set the trigger....

...the timers load the shadow registers and start Synced.

How would it work on the C2000 to get more Timers Synced? 

Thanks 

Mauro

Hi Mauro, 

To clarify are you trying to use the CPU Timers for this? Or are you talking about using the EPWMs? Are you trying to trigger ADC SOCs on three different instances of ADCs at the exact same time or staggered but the same frequency? If they are at the exact same time, you can trigger all ADC SOCs using a single PWM, but if you are staggering, you simple need to offset the PWM frequencies. Perhaps I am misunderstanding what your target configuration is though - would you be able to quick sketch out a diagram to show the expected timings you are targeting between the ADCs/timer/PWMs?

The EPWM modules can generate ADC SOCs and interrupts at a configurable rate (frequency of the PWM), and you can easily synchronize the PWMs and offset (if needed) the frequency of the PWMs so that any cyclic events (occurring every period of the PWM) take place in a staggered manner across the PWMs.

• The use of EPWMs to trigger ADC SOC events and interrupts is explained in the TRM section 26.10 Event-Trigger (ET) Submodule.
  • 
• The principle of EPWM synchronization is also explained in the TRM starting in section 26.4.3.3 Time-Base Counter Synchronization.

• The ADC examples I already mentioned showcase using the PWM to trigger ADC SOCs
• The synchronization + offset of PWM signals can be seen in our EPWM synchronization example located in {C2000Ware}\driverlib\f2838x\examples\c28x\epwm - although this doesn't showcase ADC SOCs, this can be easily configured in addition.

Best Regards,

Allison

Hello Allison,

thanks for the follow up.

We are trying to get the max sampling frequency by combining all the ADC together (4 ADC).

Each ADC will work at the maximum sampling rate. 

To get an equivalent sampling frequency 4x the maximum sampling frequency, each ADC must get the trigger 1/4 of the period of the maximum sampling frequency away from the other ADC. So that all the ADCs run at maximum speed, and every 1/4 of the period of the maximum sampling frequency each ADC gets the trigger. No ADC works at the same time, but with the trigger 1/4 of the period away. 

The synchronization of two timers or multiple PWM is important so that each ADC gets the trigger 1/4 of the period away from the other ADC. 

Using Timer or ePWM is the same, whatever solution can enable the above is ok.

From my understanding it looks the the ePWM can enable: synchronization, each PWM can trigger an ADC, I can trigger 4 ADC with 1/4 the maximum sampling period away from other ADC. 

If we can get it, we have interleaved 4 ADC.

Thanks, 

Mauro