C GPIO

[martind1983]

One more question. All the pins led out on the board and which are also dedicated to some peripherals I have to first turn off special functionality before using them as normal GPIO?

No, not necessarily.

... as long as the pins (channels) are not actually being used 'now' you can use them for what-ever you want. But, that's a big if.  If a driver is running that uses the channel, you will need to stop and unload the driver... but, you don't necessarily have to edit the dtb|dts in order to do this.

That said, it is best to use GPIO pins that are 'free' first.  On the diagram , the green and then maybe the blue. The main exception right now is the pin(7) GPIO04 which is s-pwm and used for the LCD backlight... because it is on a pwm channel even though you can turn it on and off (if you have the correct base address, or use sysfs) it still doesn't work right, because it is 'very' dim ... and, it has a pwm signal on it.  In this case you must not only edit the dtb|dts, but also unassociate the pin, and you need to stop the driver and unload it (a lot of work, just use another GPIO pin).

Hello Mark

One more question related to my issue with GPIOs. I already tried to access free pin PC4, but with the same faulty result. Below is part of my C code. Check comments. I do not understand what is the numbering of PIOs.

I use this All-winner user's manual

http://dl.linux-sunxi.org/A64/Allwinner%...20v1.0.pdf

I still do not understand why I cannot access PC4 gpio. I alos tried to change for PC6 which also is free of peripherals and the same without any response.


Thanks for your help.


// map memory image to virtual memory for direct writing in the peripherals
    // BASE_ADDR is 0x01C20000
    p_mem = mmap(NULL, page_size * 2, PROT_READ | PROT_WRITE, MAP_SHARED, fd, BASE_ADDR);
    if (p_mem == (void *) -1) {
        perror("mmap");
        exit(EXIT_FAILURE);
    }

    // convert void * to unsigned long *; gpio variable is type unsigned long pointer
    gpio = (volatile unsigned long *) p_mem;

    /*
     * add offset 0x800 to mapped base address to get to PIO registers
     * plus add offset to PC_CFG0_REG 0x48 to PC4 (PI-2 pin 32) as output,
     * &= ~(3 << 17) should set PC4 to output mode as by default pins are disabled (every pin = 0x7)
     * for output to set to log 1, the same I set offset 0x800, plus I add offset to PC_DATA_REG 0x58
     * and set 1 by |= 0x10 for PC4
     */

    *(gpio + GPIO_REG_OFFSET + 0x48) &= ~(3 << 17);
    *(gpio + GPIO_REG_OFFSET + 0x58) |= 0x10;

    while(active) {
        *(gpio + GPIO_REG_OFFSET + 0x58) |= 0x10;
        sleep(2.5);

        *(gpio + GPIO_REG_OFFSET + 0x58) &= 0x00;

        sleep(2.5);
    }

    return 0;
}