usb-gpio-board

GPIO over usb board based on vusb AVR stack

View the Project on GitHub

GPIO-12 board

This is a gpio over usb board based on VUSB stack for AVR atmega8 chip. It exposes 12 GPIO ports.

My current prototype uses USBPrayog Board from rarecomponents.com.

I shall produce an exclusive kicad schematic for this board soon. board in action

How to flash mega8

cd firmware
make hex
avrdude -c usbasp -p m8 -U flash:w:main.hex

PIN mapping

GPIO pins

Atmega8 gpio | pin number ————-| ———— PD0 | 1 PD1 | 2 PD2 | Not available (used as D+) PD3 | 3 PD4 | Not available (used as D-) PD5 | 4 PD6 | 5 PD7 | 6 PB0 | 7 PB1 | 8 PB2 | 9 PB3 | 10 PB4 | 11 PB5 | 12 PB6 | Not available (used by crystal) PB7 | Not available (used by crystal)

ADC pins

Atmega8 ADC pin | pin number ————— | ———— PC0 | 0 PC1 | 1 PC2 | 2 PC3 | 3 PC4 | 4 PC5 | 5

how to access gpio port as linux kernel sysfs

You need to load the kernel driver for this.

$ cd driver/gpio
$ make
$ sudo insmod usb-gpio12.ko
$ cd /sys/class/gpio/
gpiochip**N** where N is the value allocated by kernel
$ sudo chmod 666 export unexport
$ echo **N** > export
$ cd gpio**N**
$ echo out > direction
$ cat value
$ echo 1 > value
$ echo 0 > value

Before unloading the module, do $ echo N > unexport
gpioN gets deleted by doing so.
To unload the module, $ sudo rmmod usb_gpio12

How to control gpio pins via libusb

In case, you want to control gpio ports via libusb, follow this guide.

include following code in your application code or include the common.h file.

typedef struct __attribute__((__packed__)) _gpio_info
{
   uint8_t no;
   uint8_t data;
} gpio_info;

typedef struct __attribute__((__packed__)) _gpiopktheader
{
   uint8_t command;
   gpio_info gpio;
} gpiopktheader;

typedef struct __attribute__((__packed__)) _spipktheader
{
   uint8_t command;
   uint8_t data;
   uint8_t speed; //future;
} spipktheader;

typedef struct __attribute__((__packed__)) _adcpktheader
{
   uint8_t command;
   uint8_t gpio_no; //C0 -- C5
   uint16_t data; //ADC data is 12 bits (0 - 1024)
   uint8_t speed; //Future
} adcpktheader;

typedef enum _command
{
   BOARD_INIT, // This does the init of board
   BOARD_RESET, // This restarts the board
   GPIO_INPUT, // Set GPIO as input
   GPIO_OUTPUT, // Set GPIO as output
   GPIO_READ,   // Read GPIO
   GPIO_WRITE, // Write to GPIO
   SPI_INIT,  // Initialize SPI
   SPI_DATA,  // Send data over SPI
   SPI_END,  // End spi connection
   ADC_INIT, // Initialize ADC
   ADC_READ, // Read ADC value from ADC pin (C0 - C5)
   ADC_END,  // End ADC
} command;

high

uint8_t buffer[3];
usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                        GPIO_WRITE, gpio_number | (1 << 8), 0, buffer, 3, 1000);
gpiopktheader *reply = (gpiopktheader *)buffer;

low

uint8_t buffer[3];
usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                        GPIO_WRITE, gpio_number | (0 << 8), 0, buffer, 3, 1000);
gpiopktheader *reply = (gpiopktheader *)buffer;

usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN, GPIO_INPUT, gpio_number, 0, buffer, 3, 1000); usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN, GPIO_READ, gpio_number, 0, buffer, 3, 1000); gpiopktheader *reply = (gpiopktheader *)buffer;

uint8_t gpio_read_val = reply->val;


- Reset Board
```C
uint8_t buffer[3];
usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                        BOARD_RESET, 0, 0, buffer, 3, 1000);
gpiopktheader *reply = (gpiopktheader *)buffer;

uint8_t spi_data = 111;

nBytes = usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                                 SPI_INIT, 0, 0, 0, 0, 5000);

nBytes = usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                         SPI_DATA, 0 | (spi_data << 8), 0,
                         buffer, 3, 5000);
spipktheader *spi_info = (spipktheader *) buffer;
printf("MOSI data: %d", spi_info->data);

nBytes = usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                         SPI_END, 0, 0,
                         0, 0, 5000);


nBytes = usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                                 ADC_INIT, 0, 0,
                                 buffer, 1, 1000);

nBytes = usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                        ADC_READ, gpio_number, 0,
                        buffer, 5, 1000);

adcpktheader *adc_info = (adcpktheader *)buffer;
printf("ADC pin %d read value: %d\n", adc_info->gpio_no, adc_info->data);

nBytes = usb_control_msg(handle, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_ENDPOINT_IN,
                         ADC_END, 0, 0,
                         buffer, 1, 1000);

you can look into ubstest example for more details.

example

GPIO write speed

GPIO write speed is close to 1Khz. GPIO write speed - logic analyzer

TODOs