8-bit External Bus

[Jim Logsdon]

The NORDIC tutorials are great for demonstrating how to use GPIOs to drive LEDs and read buttons. 

However, I need an 8-bit bus to exchange bytes with an external display IC.

I did a search of the documentation, but failed to find any information on how to do it.

Thanks!

Jim

[khelmutlord]

Hello Jim,

To do this in the "proper" Zephyr way, you would need to create a custom devicetree binding. Chris Gammell at Golioth has the following blog post that may be helpful to you:

https://blog.golioth.io/zephyr-for-hardware-engineers-gpio/

There are also some examples of bit-banging different interfaces in Zephyr:

https://github.com/zephyrproject-rtos/zephyr/blob/7cef0e361467136064a066de718af12e00a9e7d9/drivers/mipi_dbi/mipi_dbi_bitbang.c#L56

That being said, if you are using MIPI-DBI (as it sounds like you may be?) it is possible to use the existing MIPI-DBI bitbang driver above.

github.com/.../zephyr,mipi-dbi-bitbang.yaml

Thanks,

Helmut Lord

[Jim Logsdon]

I gave up on Zephyr and began directly writing and reading gpio peripheral registers.   

Controlling the NORDIC pins via the peripheral registers is so easy, I don't see any reason to use the Zephyr API.  Here's my simple solution:

Specify the GPIO control register addresses:

#define PORT_OUT    (*(volatile uint32_t*)                          0x50000504)

#define PORT_OUTSET (*(volatile uint32_t*)                          0x50000508)

#define PORT_OUTCLR (*(volatile uint32_t*)                          0x5000050C)

#define PORT_IN     (*(volatile uint32_t*)                          0x50000510)

#define PORT_DIR    (*(volatile uint32_t*)                          0x50000514)

#define PORT_DIRSET (*(volatile uint32_t*)                          0x50000518)

#define PORT_DIRCLR (*(volatile uint32_t*)                          0x5000051C)

Then control them by direct writes and read them by direct reads:

    PORT_DIRSET =  0x180000;

    if (x) {

        PORT_OUTSET =  0x180000;        

    } else {

        PORT_OUTCLR =  0x180000;

    }

    int gpio_pin_values = PORT_IN;

Easy and understandable.