Ports and Pins

Our Communicators

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In computer programming a port is a communication endpoint. It completes the destination or origination network address of a message. Specific port numbers are reserved to identify specific services so that an arriving packet can be easily forwarded to a running application.

Every microcontroller has pins in it to attach power connections, input and output connections, and communications connections. Every microcontroller has different configurations for its pins, and often one pin will have more than one function.

Pins are grouped into ports, and all of a pin’s settings are controlled from the port’s register block. We’d like each pin to be a self-contained struct, so that ownership of it can be passed from one software module to another, and only the owning module can mutate its pins. This follows Rust’s one-owner rule for pins, but would require that each pin be able to mutate its settings in the Port register block.

Struct Definitions

Port

pub struct Port {/*fields ommited*/}

Port represents a struct containing the register definition for a Port namely:

• pin : Port input pins. Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.

• ddr : Data direction register. The DDxn bit in the DDRx register selects the direction of this pin. If DDxn is written logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin.

• port: Data register. If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as an output pin. The port pins are tri-stated when reset condition becomes active, even if no clocks are running. If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).

More about these registers can be found in Section 13.2.1 and 13.2.2 of ATmega328P datasheet and Section 13.2 to 13.4 of ATMEGA2560P datasheet.

Pin

pub struct Pin {/*fields omitted*/}

Pin represents struct corresponding to a pin namely:

• port : pointer of type struct Port
• pin : Pin number of type usize

Pins

pub struct Pins { /*fields omitted */}

All pins inside a single struct:

• analog : controls the analog pins of the chip.
• digital : controls the digital pins of the chip.

Enums

PortName

pub enum Portname {/*fields ommited*/}

Lists all ports available on the chip.

• Ports A to D except A are available on atmega328p.
• Ports A to L except I are available on atmega2560p_.

Trait Implementations

Impl new for Port

pub fn new(name: PortName) -> &'static mut Port

Usage:

use rustduino::hal::port::*;

let mut port = Port::new(Portname::B) // here B is the port name.

// port is the pointer to the struct.

// we will use the port variable for demonstration of other functions also.

Matches a valid PortName and returns a struct containing register definition of the chosen Port.

Impl pin for Port

pub fn pin(&mut self, p: usize) -> Pin

Usage:

port.pin(pin number:u8) // here pin number can range from 0 to 7

Returns a pin struct for given pin.

Impl set_pin_mode for Port

pub fn set_pin_mode(&mut self, p: usize, mut mode: u32)

Sets the pin mode, given the pin and requested mode.

Impl make_gpio for Pin

pub fn make_gpio(self) -> Gpio

Sets pin to GPIO mode