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README_PORTS.md

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Ports

Avr Atmegas access and control pins through registers. The registers are 8 bit wide and up to 8 pins are therefore controlled with every register.

  • The DDR registers controls the data directions.
  • The PORT registers the output or the pull up resistors.
  • The PIN registers toggle the output or are used to read values from pins.

All pin selections in this library are done using typedefs. See below for an example.

DDR, PORT and PIN of every pin may be accessed through the static fields ::DDR, ::PORT and ::PIN on those typedefs.

Data direction and pull-up resistor may also be set using enums. (Note that the compiler is able to verify that a data direction enum is only used on register DDR! Macros would not be able to do so.)

The ports namespace also provides some helper functions to efficiently assign multiple values.

Doxygen documentation

The ports subsystem is documented in the: namespace ports

typedefs

The pin layout is compatible to arduino / arduino lite.

Prefix names in the following graph with PIN_ to get provided typedefs. Example: B5 → PIN_B5, 8 → PIN_8

                                 ┏━u━┓
                     C6    DIP_1 ┃   ┃ DIP_28   19   C5   ADC5   SCL
RXD              0   D0    DIP_2 ┃   ┃ DIP_27   18   C4   ADC4   SDA
TXD              1   D1    DIP_3 ┃   ┃ DIP_26   17   C3   ADC3
        INT0     2   D2    DIP_4 ┃   ┃ DIP_25   16   C2   ADC2
OC2B    INT1     3   D3    DIP_5 ┃   ┃ DIP_24   15   C1   ADC1
XCK     T0       4   D4    DIP_6 ┃   ┃ DIP_23   14   C0   ADC0
                             VCC ┃   ┃ GND
                             GND ┃   ┃ AREF
XTAL1   TOSC1   20   B6    DIP_9 ┃   ┃ AVCC
XTAL2   TOSC2   21   B7   DIP_10 ┃   ┃ DIP_19   13   B5   SCK
T1      OC0B     5   D5   DIP_11 ┃   ┃ DIP_18   12   B4   MISO
AIN0    OC0A     6   D6   DIP_12 ┃   ┃ DIP_17   11   B3   MOSI   OC2A
AIN1             7   D7   DIP_13 ┃   ┃ DIP_16   10   B2   SS     OC1B
ICP1    CLK0     8   B0   DIP_14 ┃   ┃ DIP_15    9   B1          OC1A
                                 ┗━━━┛

Pins VCC, GND, AREF and AVCC are only for documentation and don't provide typedefs.

Setting or reading single DDR, PORT or PIN bits:

typedef PIN_C2 Pin_In;   // Give PIN_C2 a meaningful name.

// Use your favorite way of setting DDR of pin C2:
Pin_In::DDR = 0;         // PIN_C2::DDR = 0; would work as well.
Pin_In::DDR = ports::DataDirection::Read;  // Use the (safer) provided enum.
Pin_In::setDD(ports::DataDirection::Read); // Equivalent to the previous line.

Pin_In::setToInput(ports::PullUp::HighZ);  // Sets DDR and then PORT (pullup).

uint8_t i = Pin_In::PIN; // Read a value.

Assigning / Reading multiple DDR, PORT or PIN bits in an optimized way:

// Set the DDR bit on different pins:
//   assign bit         7       6       5           4       3       2       1      :  76 4321
set_8_byte<IOReg::DDRx, PIN_B1, PIN_D2, PIN_UNUSED, PIN_D4, PIN_D5, PIN_D3, PIN_D7>(0b11110000);

uint8_t x1 = get_8_byte<IOReg::DDRx,
                        PIN_B1, PIN_D2, PIN_UNUSED, PIN_D4, PIN_D5, PIN_D3, PIN_D7>();
// Unused pins are read as 0.
// 0b11010000 if called after the previous set_8_byte.

// Specify which bit should be assigned to which pin:
set_8_bits<IOReg::DDRx,
           PIN_D7, 1, // extract bit 1 and assign to PIN_D7
           PIN_D3, 2, // extract bit 2 and assign to PIN_D3
           PIN_B1, 7,
           PIN_D2, 6,
           PIN_D4, 4,
           PIN_D5, 3>(0b11110000);
// Equivalent to previous set_8_byte instruction.

// Specify which bit in returned value is which pin:
uint8_t x2 = get_8_bits<IOReg::DDRx,
                        PIN_D7, 1,
                        PIN_D3, 2,
                        PIN_B1, 7,
                        PIN_D2, 6,
                        PIN_D4, 4,
                        PIN_D5, 3>();
// Equivalent to previous get_8_byte instruction.

//                bit in value v       v       v       v         vvvv
//                         3+3=6   2+3=5   1+3=4   0+3=3   ↓offs 6543
set_4_nibble<IOReg::PORTx, PIN_B1, PIN_D3, PIN_D2, PIN_D1, 3>(0b00101100);

Assigning / Reading multiple bits from provided registers in an optimized way:

// For all get* / set* functions a version where you have to
// provide regB, regC and regD exists.  (Except set_4_nibble).
uint8_t rB = 0, rC = 0, rD = 0;
set_8_byte<PIN_B1, PIN_D2, PIN_UNUSED, PIN_D4, PIN_D5, PIN_D3, PIN_D7>(rB, rC, rD, 0b11110000);
// rB becomes 0b00000010  (because of B1)
// rD becomes 0b00010100  (because of D2 and D4)
// D5, D3 and D7 would set corresponding bits in rD to 0.

Enums:

enum class DataDirection {
  Read = 0,  Input = Read,   In = Read,
  Write = 1, Output = Write, Out = Write
};
enum class PullUp {
  Off = 0, HighZ = Off,
  On = 1
};
enum class IOReg {
  DDRx, PORTx, PINx
};

Complete examples:

Turn on an Led on pin C2.

typedef PIN_C2 Led;

Led::DDR = ports::DataDirection::Output;   // Put Led pin into output mode.
Led::PORT = 1;  // Set Led pin output to high. (I.e. turn it on.)

Note that the compiler is able to optimize the Led::xxx assignments into simple sbi calls.