[FAQ] TDA4VH: TIMER in Capture Mode.

I am attaching the patches for enabling Capture using timer IO :

Uboot Driver Changes:

0001-TIMER-CAPTURE-DTBO-ENV-OVERLAY.patch

Linux Driver Changes:

0001-TIMER-CAPTURE-DRIVER-CHANGES.patch

Linux Device tree Changes:

1072.0002-TIMER-CAPTURE-DTS-changes.patch

DTBO:

k3-j784s4-dmtimer-cap.dtbo

Steps:

• Apply all the patches above.
• Once these patches are applied, recompile uboot and linux by running the below commands from the SDK directory:

  • >make u-boot
    >make linux

• Copy the following files to boot directory of sd card:
  • <SDK dir>/board-support/<u-boot dir>/build/r5/tiboot3.bin
  • <SDK dir>/board-support/<u-boot dir>/build/a72/tispl.bin
  • <SDK dir>/board-support/<u-boot dir>/build/a72/u-boot.img
• Copy the following files to <SD CARD root directory>/boot
  • <SDK dir>/board-support/<linux dir>/arch/arm64/boot/Image
• Copy the following files to <SD CARD root directory>/boot/dtb/ti
  • <SDK dir>/board-support/<linux dir>/arch/arm64/boot/dts/ti/k3-j784s4-evm.dtb
  • k3-j784s4-dmtimer-cap.dtbo file attached above.
• Run the below script to start the capture

  • #!/bin/bash
    
    #set -x
    
    cd /sys/class/pwm/pwmchip0
    echo 0 > export #Will export pwm0 device 
    cd pwm0/
    echo 100000000 > period #In nanoseconds
    echo 30000000 > duty_cycle #In nanoseconds
    echo "normal" > polarity
    echo 1 > enable
    
    while true
     do
      cat capture
      sleep 2
     done

• Set the GPO_CFG bit of TIMER_TCLR register for TIMER0 as 1(Capture mode) using the below commands:

  • devmem2 0x02400038 w 0x00004043
    
    

  • This is to ensure that more current is not consumed when other timers are configured in Capture mode. The reason is as follows:
    
    • Reference E2E : (+) PROCESSOR-SDK-J784S4: More Current is required to pull the TimerIO configured pins - Aptiv Jacinto Forum - APTIV - EP Automotive - TI E2E support forums
    • 1) By default all TIMERIOs OUTPUT is driven by TIMER0 as default value of mapping to TIMERs is 0. Attached here for a reference.

      

    • 2) Also, TIMER0 enables PWM by default as per default value of registers. Attached here for reference.
      

    • So, by default all TIMERIOs out is controlled by TIMER0.

Note : 

Ensure that the uENV.txt file "name_overlays" parameter(if present)  does not overwrite the name_overlays parameter given in the patch  0001-TIMER-CAPTURE-DTBO-ENV-OVERLAY.patch.

• This can be ensured by either removing the uENV.txt file or adding the "name_overlays" parameter given in the 0001-TIMER-CAPTURE-DTBO-ENV-OVERLAY.patch to the uENV.txt file.

Limitations:

The time period values are captured correctly.

However, the duty cycle values may not be accurate as timer has only 2 capture registers and these registers can be captured with cap1 in rising and cap2 in falling or vice versa. Hence, either (duty cycle) or (1-duty_cycle) will be captured. This is a hardware limitation of the IP actually.

Regards

Gokul