GPIO Usage & Used Pins

A GPIO is a software-controllable peripheral used to configure the device IO ports, also called pins.

GPIOs are grouped in ports and so each GPIO has an identifier.
The identifiers have the following format: PXY, where X is the port name and Y is the pin number.

Configuration

WARNING: Before using a GPIO it has to be correctly configured. A lot of times you can experience non-working code or drivers due to not initialized or configured GPIOs.

Examples of possible configurations for a GPIO are:

• Output: the pin voltage level can be set (logic level high or low)
• Input: the pin voltage level can be read (logic level high or low)
• Alternate Function: set the GPIO to be controlled by some hardware peripheral, such as an SPI, I2C, UART or timer. You should check your microcontroller's datasheet to know which pins have some alternate function.

Other possible modes are: analog input, input pull-up, input pull-down, open drain, alternate open drain.

The available pin modes and speeds can be found in the gpio_impl.h inside libs/miosix-kernel/miosix/arch/<your_arch>/common/interfaces-impl, according to the microcontroller you are using.

If you want to know more about GPIOs, check out the GPIO Tutorial - Miosix Wiki page.

Examples

1. Template API

To use a pin in your board you can simply do:

typedef miosix::Gpio<GPIOA_BASE, 5> somePin; // Define pin PA5 as somePin

To read from that pin:

somePin::mode(Mode::INPUT); 
int value = somePin::value();

To set the pin's logical voltage:

somePin::mode(Mode::OUTPUT);
somePin::high();
somePin::low();

To set the pin's alternate function:

somePin::mode(Mode::ALTERNATE);
somePin::alternateFunction(5);  // Specify the alternate function number

The above method provides optimal performance.

2. GpioPin Class

As an alternative you can use the GpioPin class.

GpioPin somePin(GPIOA_BASE, 5);

somePin.mode(Mode::OUTPUT);
somePin.high();

somePin.mode(Mode::ALTERNATE);
somePin.alternateFunction(5);

WARNING: when configuring GPIOs you should disable interrupts to avoid concurrent calls to mode() (for example if it is done at runtime). This can be done since pins configuration is a very fast operation, but it should in general be avoided, in order not to compromise real-time capabilities of Miosix. A normal mutex would introduce more overhead.

void someFunction()
{
   {
       FastInterruptDisableLock dLock; // disable interrupts
       somePin::mode(Mode::OUTPUT);
   } // dLock scope ends: re-enable interrupts
}

Discovery Board Pins

These are some commonly used pins that you'll need when writing software for Discovery boards.

• STM32F429ZI_DISCO

  stm32f429zi
  Red Led	PG13
  Green Led	PG14
  User Button	PA0

You can find a complete pin usage description here.

• STM32F407VG_DISCO

  stm32f407vg
  Blue Led	PD15
  Red Led	PD14
  Orange Led	PD13
  Green Led	PD12
  User Button	PA0

You can find more in the datasheet for more.

Miosix Used Pins

These are some pins that are used by default from the kernel when running on STM32 micros (all paths are referred to /libs/miosix-kernel/miosix):

• SD memory: arch/common/drivers/sd_stm32f2_f4.cpp

  D0	D1	D2	D3	CLK	CMD
  PC8	PC9	PC10	PC11	PC12	PD2

• Serial Ports: arch/common/drivers/serial_stm32.cpp

  USART	TX	RX	CTS	RTS
  1	PA9	PA10	PA11	PA12
  2	PA2	PA3	PA0	PA1
  3	PB10	PB11	PB13	PB14

• Servo: arch/common/drivers/servo_stm32.cpp

  SERVO1	SERVO2	SERVO3	SERVO4
  PB6	PB7	PB8	PB9

Extra

STM32F429ZI Discovery Pins