RPi 40-pin header programming

TI J72e SK development board contain a 40 pin GPIO header, similar to the 40 pin header in the Raspberry Pi. These GPIOs can be controlled for digital input and output using the Python/CPP libraries provided in the TI GPIO Library packages. The libraries have the same API as the RPi.GPIO library for Raspberry Pi in order to provide an easy way to move applications running on the Raspberry Pi to the TI board.

TI GPIO Libraries are packaged under /opt directory. Run the below script to build and install the gpio libraries

root@tda4vm-sk:/opt/edge_ai_apps# ./scripts/install_ti_gpio_libs.sh

By default, the 40-pin header is not enabled on TDA4VM SK board. This can be enabled by specifying the dtb overlay file k3-j721e-sk-rpi-exp-header.dtbo in /run/media/mmcblk0p1/uEnv.txt as given below.

name_overlays=k3-j721e-edgeai-apps.dtbo k3-j721e-sk-rpi-exp-header.dtbo

Reboot the board after editing and saving the file.

40-pin header default configuration

The default pin configuration on the SK board is as follows. Any deviation from this needs modifications to the Linux DTBO. The table below lists pin numbers in all three supported modes, namely BOARD, BCM, and SOC.

BOARD: Physical Pin Number BCM : Broadcom SOC Numbering SOC : TI SOC Naming

_images/j721esk_exp_hdr.png

BOARD

BCM

SOC

Function

3

2

GPIO0_84

I2C SDA

5

3

GPIO0_83

I2CSCL

7

4

GPIO0_7

GPIO

8

14

GPIO0_70

GPIO

10

15

GPIO0_81

GPIO

11

17

GPIO0_71

GPIO

12

18

GPIO0_1

GPIO

13

27

GPIO0_82

GPIO

15

22

GPIO0_11

GPIO

16

23

GPIO0_5

GPIO

18

24

GPIO0_12

GPIO

19

10

GPIO0_101

GPIO

21

9

GPIO0_107

GPIO

22

25

GPIO0_8

GPIO

23

11

GPIO0_103

GPIO

24

8

GPIO0_102

GPIO

26

7

GPIO0_108

GPIO

29

5

GPIO0_93

HW PWM

31

6

GPIO0_94

HW PWM

32

12

GPIO0_98

HW PWM

33

13

GPIO0_99

HW PWM

35

19

GPIO0_2

GPIO

36

16

GPIO0_97

GPIO

37

26

GPIO0_115

GPIO

38

20

GPIO0_3

GPIO

40

21

GPIO0_4

GPIO

NOTE: Please refer to SK-TDA4VM User’s Guide for details on the expansion header pin names and functionality. Also refer to section 2.1.2 Power Budget Considerations for power/voltage limits on the expansion header pins.

Constraints on the HW PWM functionality

The physical pins 29, 31, 32, and 33 support HW PWM functionality.

  1. All four pins are individually controllable with a few constraints noted below:

    1. Pin pair {29, 31} is internally linked to a common HW block. If both pins are enabled, then they must be programmed to the same frequency.

    2. Pin pair {32, 33} is internally linked to a common HW block. If both pins are enabled, then they must be programmed to the same frequency.

  2. The duty cycle on each of the HW pins can be controlled independently, whether they belong to the same pin-pair or not.

  3. If both pins of a given pin-pair are enabled and if a frequency change needs to be made on the pin-pair, then follow the sequence below:

    1. Disable PWM operation on one of of the pins

    2. Update the frequency on the active pin with new_frequency

    3. Setup the disabled pin with new_frequency and enable it

    This is the only case where the operations across pins need to be co-ordinated when using the Python or CPP GPIO API.

Repositories

The Python and CPP projects are hosted on Texas Instruments githib. The links to the projects are given below. The details on installation and testing can be found in the respective project documentation.

Python Library: https://github.com/TexasInstruments/ti-gpio-py.git

CPP Library: https://github.com/TexasInstruments/ti-gpio-cpp.git

The above repositories are cloned and installed during the initialization process upon initial boot. The gpiozero library is also installed as a part fo the initialization.

Additional References

Please refer to the lik below for information on the 40-pin header numbering and naming conventions:

https://pinout.xyz/#