{"id":4042,"date":"2020-05-27T18:16:24","date_gmt":"2020-05-27T23:16:24","guid":{"rendered":"https:\/\/dev.iachieved.it\/iachievedit\/?p=4042"},"modified":"2020-05-27T18:16:24","modified_gmt":"2020-05-27T23:16:24","slug":"hifive1-rev-b-gpio-pins","status":"publish","type":"post","link":"https:\/\/dev.iachieved.it\/iachievedit\/hifive1-rev-b-gpio-pins\/","title":{"rendered":"HiFive1 Rev B GPIO Pins"},"content":{"rendered":"

Let’s make use of the HiFive1 Rev B<\/a> schematics<\/a> to map out the GPIO controller device pins. Of particular interest is sheet 3, and the following components of the schematic in section D1:<\/p>\n

\"\"<\/a><\/p>\n

We’re going to use this as our starting point. Three GPIO lines labeled 19, 21, and 22 with LEDs on the lines.<\/p>\n

Editor’s Note<\/em>: This write-up on the SiFive HiFive1 Rev B assumes you have one and are familiar with powering it up, connecting to the serial port, and uploading applications. See our last post<\/a> if you need to orient yourself with the environment.<\/p>\n

Using Metal GPIO<\/h2>\n

If you haven’t done so already, familiarize yourself with Freedom Metal<\/a> and the API documentation<\/a> because we’re going to make use of the GPIO functions<\/a>.<\/p>\n

Recall in the schematic above that the onboard LEDs are tied to GPIO 19 (green LED), GPIO 21 (blue LED), and GPIO 22 (red LED). While the Metal LED API<\/a> could be used here, we’re going to work directly with the GPIO functions to prove to ourselves that the above GPIO pins are correct, and also check out the 8 color combinations the LED can produce.<\/p>\n

Our basic loop is going to cycle from 0 to 7 and turning on the red LED if bit 1 is set, the green LED if bit 2 is set, and the blue LED if bit 3 is set. This should cause our HiFive1 on-board LED to cycle through the following color chart:<\/p>\n

\"\"<\/a><\/p>\n

Okay, let’s get the basics down. The GPIO can be accessed by obtaining a struct metal_gpio*<\/code> using the metal_gpio_get_device<\/code> function, like this:<\/p>\n

\n#include \n\nint main(void) {\n  \/\/ Get GPIO device\n  struct metal_gpio* gpio_device = metal_gpio_get_device(0);\n\n  \/\/ do something with the GPIO\n}\n<\/pre>\n
Now that we have the GPIO device itself, let’s enable GPIO 19 as an output pin.  In our schematic take note that the other side of the LED is tied to 3.3V.  In other words<\/strong>, there is no setting GPIO 19 high or low required here, if it is enabled you’re going to get the LED on.<\/p>\n
To set GPIO 19 as an output:<\/p>\n
\nmetal_gpio_enable_output(gpio_device, 19);\n<\/pre>\n
To disable the output of the pin:<\/p>\n
\nmetal_gpio_disable_output(gpio_device, 19);\n<\/pre>\n
Now I think<\/i>this works for the onboard LED because of the way it is wired to the 3.3V supply.  In fact, for Metal GPIO pin 19, if you try to write a 1 to it you actually turn off the onboard LED and turn on the header pin 3.  Speaking of the header pins…<\/p>\n
Arduino Header and Pins<\/h2>\n
Going back to the board schematic, this time on sheet 3 in sections A5, A6, B5, B6, and C5, C6.<\/p>\n
\"\"<\/a><\/p>\n
Now this is interesting!  Our Arduino headers as well have notes on which GPIOs are digital-only (high or low), those that are PWM-capable, and which pins are shared by SPI, I2C, and UART.  All we need to do is put this into a nice table, and the following is (I think) a complete GPIO mapping for the SiFive HiFive1 Rev B board.<\/p>\n
\"\"<\/a><\/p>\n
For example, if you wanted to start your project with blinking an LED on a breadboard, you might start with one of the “standard” digital input\/output pins on the header, say pin 7.  The chart above (which is derived from the schematic) shows that pin 7 on the header is tied to pin 23 of the GPIO controller.  So to use header<\/em> pin 7 we might write:<\/p>\n
\nmetal_gpio_enable_output(gpio_device, 23);\nmetal_gpio_set_pin(gpio_device, 23, 1);\n<\/pre>\n
Or, we could set at the top of our file something along the lines of #define PIN7 23<\/code>.  Just a thought.<\/p>\n
Notice once again that this mapping table shows that there are:<\/p>\n