PROCESSOR-SDK-AM64X: PRU 16 Bit Input Capture

Hello Burak,

There are several examples you can take a look at.

This code was written specifically for AM64x with several different TI ADCs:
https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/09_00_00_31/exports/docs/api_guide_am64x/DRIVERS_PRU_ADC.html

This TI Design Flexible Interface (PRU-ICSS) Reference Design for Simultaneous, Coherent DAQ Using Multiple ADCs was developed on AM335x, but the concepts also apply to AM64x. The software can be found in your Linux Processor SDK under example-applications/pru-adc-x.x.x, or at the TIDA-01555 git repo. This example uses the PRU to control external ADCs by implementing the SPI protocol. The SPI code that collects ADC samples is under folder PRU_ADS8688_Interface. The control code that implements interrupts and data transfer from PRU to ARM is under folder PRU_ADS8688_Interface.

Regards,

Nick

Part Number: PROCESSOR-SDK-AM64X

Hello everyone,
I have a 16 bit ADC integrated and this ADC data is given via parallel communication over 16 pins.
For this reason, I want to use the 16-Bit Parallel Capture feature of the AM64 PRU unit. (6.4.5.2.2.3.2 PRU EGPIs 16-Bit Parallel Capture -AM64x /AM243x Processors Silicon Revision 2.0) Do you have any documents on this subject that can serve as a reference for me? I also need to sample the data with 32 Mhz. Do the PRU and DMA unit support this speed? How can I create this structure if it supports it? I want to process this data I receive using the PRU and DMA unit in the R5 core.

Hello Burak,

I have merged your new thread back into this thread since I think it makes sense to continue the conversation here.

In terms of PRU's ability to sample a signal at the processor pin, please reference this response here:
https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1293208/am625-pru-eqep-pto-issues/4909395#4909395

The DMA is not related to the PRU's ability to sample a signal at the pin.

You can see one implementation of inter-processor communication (IPC) between the PRU and the R5F cores in the MCU+ SDK docs here:
https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/09_00_00_31/exports/docs/api_guide_am64x/DRIVERS_PRU_IPC.html

Regards,

Nick

Can I read the r31 register of the pru core from the r5 core? If I can't read it, do I need to write separate code for both cores?

Hi Burak,

No, The R31 register is an internal PRU register and can not be accessed directly from the R5 core.

For your usecase, you can see the PRU ADC parallel interface example with AM64x: https://software-dl.ti.com/mcu-plus-sdk/esd/AM64X/09_00_00_31/exports/docs/api_guide_am64x/EXAMPLES_PRU_ADC_ADS85x8.html

The example does the following:

- PRU controls the ADC, reads the samples and implements the samples transfer interface

- PRU then writes the samples to a shared memory and creates an interrupt after writing 1 block of data.

- On interrupt R5F reads the data and can do post processing on it.

Regards,

Nitika

Thank you for your answers. I have one more question. I have an ADC integrated and it samples data at 32 Mhz. I need to take this sampled data using the 16-bit parallel input capture mode of the Pru unit and write it to the shared memory of the Pru core. Can I do this without missing data? Is this possible? Because the data is sampled at 32 Mhz.

(AM64's datasheet (page 210 parallel capture timing) says that the clock pin can sample at a speed of 20 ns.)

I cannot test it myself because I cannot provide an input signal to the gpio pins at a speed of 32 Mhz.
If it is possible, I will choose this MCU to use in my project.

Hi Burak,

Please help me with a few questions about your use case for more clarity:

1. I assume you have 16 channels on your ADC, is that correct?

2. Do you want trigger based capture or continuous sampling of data?

3. Just to confirm, you want to provide the sampling clock from PRU? 

4. As you mentioned you want to sample data at 32 MHz, you expect a sampling frequency of 32MSPS or 32Mbps?

Regards,

Nitika

I shared the block diagram I wanted to make in the picture below. If there is something you do not understand, you can ask. My question is, while I receive the data with the Pru unit, can the Pru unit capture this data at such a high speed and can I write to the shared memory without losing the data?

Hello Burak,

Ok, let's stop for a minute to make sure you understand what you are asking for.

There are 2 PRU GPI modes that capture the signal values on a bunch of pins all at the same time:

1) "Direct input" mode is the default mode. Up to 20 PRU GPI signals are all captured on every single PRU's internal clock cycle, and can be read from the internal register R31

2) "Parallel capture mode" is like direct input mode, but now the PRU GPI values stored in register R31 are only updated whenever that external CLOCKIN signal goes high (or low, depending on how you program it), instead of getting updated every PRU clock cycle

Are you specifically asking about parallel capture mode, with the external CLOCKIN signal? Or do you just want to capture 16 bits in a single clock cycle? 

Regards,

Nick

I want to use Parallel capture mode with external clockin signal.The data ready pin of the ADC will provide the input for my external clock pin. Because my data will be sampled every 32 Mhz.

Hi Burak,

I will discuss this requirement internally and get back to you.

Regards,

Nitika

Hello Burak,

It will be helpful if you can share the ADC part number you are using to understand the requirement better.

From your requirement:

• You are sampling at 32MSPS 16bit resolution, i.e., you get 1 new sample every 31.25ns.
• You want to process the received samples using R5F core.

As Nick mentioned earlier we have 2 modes in which pins can be configured.

• Using direct input mode -  It should be possible to get this working.
• Using parallel capture mode - as you want to capture on rise edge, it should be possible. 

Regards,

Nitika