Blink
=====

.. include:: ../substitutions.rst
.. include:: ../../common/applicationdevelopment/linux/Blink1.rst

.. code-block:: c

    #include <sys/mman.h>
    #include <fcntl.h>
    #include <unistd.h>
    #include <time.h>

    // Setup GPIO4_IO05
    #define GPIO4_ADDR_START 0x30230000
    #define GPIO4_ADDR_END 0x3023001C
    #define GPIO4_SIZE (GPIO4_ADDR_END - GPIO4_ADDR_START)
    #define GPIO4_PORT (1 << 5)
    #define GPIO_DATA_OFFSET   0x000000000
    #define GPIO_DIR_OFFSET    0x000000004

    void *gpioAddress;
    unsigned int *gpio_setdataout_addr;
    unsigned int *gpio_direction_addr;

    void delay(unsigned long ms)
    {
        clock_t start_ticks = clock();
        unsigned long millis_ticks = CLOCKS_PER_SEC / 1000;
        while (clock() - start_ticks < ms * millis_ticks){}
    }

    int main()
    {
        int fd = open("/dev/mem", O_RDWR);

        gpioAddress = mmap(0, GPIO4_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, GPIO4_ADDR_START);

        close(fd);

        gpio_setdataout_addr  = gpioAddress + GPIO_DATA_OFFSET;
        gpio_direction_addr   = gpioAddress + GPIO_DIR_OFFSET;

        *gpio_direction_addr |= GPIO4_PORT;

        while (1)
        {
            *gpio_setdataout_addr |= GPIO4_PORT;
            delay(1000);
            *gpio_setdataout_addr &= ~(GPIO4_PORT);
            delay(1000);
        }
    }


.. include:: ../../common/applicationdevelopment/linux/Blink2.rst

Mux the Processor Pin
---------------------

In order for this blink executable to work as intended, we also need to ensure that the processor pad is multiplexed such that the |blink-signal| signal is enabled and configured as an output on the |blink-pad| processor pad. We can do this easily using the 'devmem2' utility to directly access and modify the |soc-caps| hardware registers.

.. warning::
    Use caution when working with the 'devmem2' utility as it gives you direct access to read and write to memory that could render the system unstable if you modify memory that is being actively used. This utility has no error checking and shouldn't be relied upon in production software. PHYTEC recommends working with 'devmem2' only while prototyping and transitioning your pin settings to the linux device tree for production.

* First, identify the processor pad that brings out the signal we are targeting. This can be done by following |blink-net| in the carrier board schematic back to the SOM and to the |soc-caps| processor itself. You should find that this signal is accessible at the processor ball number |blink-ballnum|\ , named |blink-pad|\ .
* Looking up the |blink-pad| processor pad within the |soc-caps| TRM, we can see that this pad is configured within the |blink-padcfg| register which has the memory address |blink-padcfg-addy|.
* We can read this register like so:

**Target (Linux)**

.. parsed-literal::

    devmem2 |blink-padcfg-addy|

* We should see the following output by default:

**Example Output**

.. parsed-literal::

    root@\ |default-machine-name|\ :~# devmem2 |blink-padcfg-addy|
    /dev/mem opened.
    Memory mapped at address 0xffff9fc5f000.
    Read at address  |blink-padcfg-addy| (0xffff9fc5f084): |blink-padcfg-default-val|

* The value held in the |blink-padcfg| memory address is |blink-padcfg-default-val|, which can be broken down according to the |blink-padcfg| Register Field Descriptions within the TRM (see |blink-padcfg-desc|\ ). Here we can see that the register is already configured in the GPIO mode we need, so in this case there are no pad config changes necessary.

.. include:: ../../common/applicationdevelopment/linux/Blink3.rst

.. image:: ../../images/phycore-imx7/imx7-blink-circuit.webp
   :width: 500px
   :alt: Example circuit for blinking an LED connected to the phyCORE-AM62x Development Kit.

.. include:: ../../common/applicationdevelopment/linux/Blink4.rst