Wikibooks: C-Programmierung mit AVR-GCC

mikrocontroller.net: AVR-GCC-Tutorial
mikrocontroller.net: AVR-GCC-Tutorial/LCD-Ansteuerung
mikrocontroller.net: AVR-GCC-Tutorial/Analoge Ein- und Ausgabe
mikrocontroller.net: AVR-ASM-Tutorial
mikrocontroller.net: Bitmanipulation

Pin Change Interrupt (PCINT) mit dem ATMega oder Arduino
Pin-change interrupts on Arduino

Tuxgraphics: AVR C-programming tutorial

RN-Wissen: AVR
RN-Wissen: AVR-Einstieg leicht gemacht
RN-Wissen: AVR-GCC

conelek: AVR C: Softwareentwicklung mit dem AVR Studio 5

ladyada: AVR Tutorial

SiSy avr-cpp: AVR C++ Tutorial

pgm_read_byte()

Abstract

The pgm_read_byte() is a macro that reads a byte of data stored in a specified address(PROGMEM area).

Source Code

The pgm_read_byte() is defined in hardware/tools/avr/avr/include/avr/pgmspace.h as below.

#define pgm_read_byte(address_short)    pgm_read_byte_near(address_short)

The input is address_short and calls the pgm_read_byte_near() macro.

pgm_read_byte_near()

Abstract

The pgm_read_byte_near() is a macro that reads a byte of data stored in a specified address(PROGMEM area).

Source Code

The pgm_read_byte_near() is defined in hardware/tools/avr/avr/include/avr/pgmspace.h as below.

#define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))

The input is address_short and the macro converts the address_short to uint16_t, then calls __LPM() macro.

__LPM()

Abstract

The __LPM() is a macro that reads a byte of data stored in a specified address(PROGMEM area).

Source Code

The __LPM() is defined in hardware/tools/avr/avr/include/avr/pgmspace.h as below.

#define __LPM(addr)         __LPM_enhanced__(addr)

The input is addr and just calls __LPM_enhanced__().
See Intrinsic Functions

__LPM_enhanced__()

Abstract

The __LPM_enhanced() is an assembler code that reads a byte of data stored in a specified address(PROGMEM area).

Source Code

The __LPM_enhanced() is defined in hardware/tools/avr/avr/include/avr/pgmspace.h as below.

#define __LPM_enhanced__(addr)  \
(__extension__({                \
    uint16_t __addr16 = (uint16_t)(addr); \
    uint8_t __result;           \
    __asm__                     \
    (                           \
        "lpm %0, Z" "\n\t"      \
        : "=r" (__result)       \
        : "z" (__addr16)        \
    );                          \
    __result;                   \
}))

or newer avr-libc

#define __LPM_classic__(addr)   \
(__extension__({                \
    uint16_t __addr16 = (uint16_t)(addr); \
    uint8_t __result;           \
    __asm__                     \
    (                           \
        "lpm" "\n\t"            \
        "mov %0, r0" "\n\t"     \
        : "=r" (__result)       \
        : "z" (__addr16)        \
        : "r0"                  \
    );                          \
    __result;                   \
}))

The lpm, short for Load Program Memory, is a instruction that reads a byte of data from PROGMEM area. It substitue a data at addr for __result, then returns the __result.

Sources:
pgm_read_byte() marco
pgm_read_byte_near() marco
__LPM() marco
__LPM_enhanced__() marco

/* pin = Arduino Mapped Pin Name, ex. Digital pin 22: pin = 22 */
void digitalWrite(uint8_t pin, uint8_t val)
{
    uint8_t timer = digitalPinToTimer(pin);
    uint8_t bit   = digitalPinToBitMask(pin);
    uint8_t port  = digitalPinToPort(pin);

    volatile uint8_t *out;
    out = portOutputRegister(port);

    uint8_t oldSREG = SREG;
    cli();

    if (val == LOW) {
        *out &= ~bit;
    } else {
        *out |= bit;
    }
    
    SREG = oldSREG;
}

SREG (Status Register) und Globale Interrupts aktivieren: SREG -Register

extern const uint8_t PROGMEM digital_pin_to_port_PGM[];

#define digitalPinToPort(P) ( pgm_read_byte( digital_pin_to_port_PGM + (P) ) )

#define pgm_read_byte(address_short)    pgm_read_byte_near(address_short)
#define pgm_read_byte_near(address_short) __LPM((uint16_t)(address_short))

Was pgm_read_byte() macht bzw. wie es in Assembler übersetzt wird: Source von pgm_read_byte

C:\arduino-1.0.4\hardware\tools\avr\avr\include
C:\arduino-1.0.4\hardware\arduino\cores\arduino

const uint16_t PROGMEM port_to_mode_PGM[] = {
    NOT_A_PORT,
    &DDRA,
    &DDRB,
    &DDRC,
    &DDRD,
    &DDRE,
    &DDRF,
    &DDRG,
    &DDRH,
    NOT_A_PORT,
    &DDRJ,
    &DDRK,
    &DDRL,
};

/arduino/variants/mega/pins_arduino.h
Accessing data past 64k boundary on atmega1280

Generating the hex file

Shift key + ‘Verify’ button

Source:

[1] Using an Arduino to Program an AVR

Gyroscope, Acceleration and Compass

Humidity and Temperature

AM2302 (wired DHT22) temperature-humidity sensor
Sensirion Temperature/Humidity Sensor – SHT11
Arduino – Temperatur und Luftfeuchtigkeit mit dem DHT22 prüfen.

Erfahrungen mit 1-Wire Temp/Feuchte-Sensor AM2305 (anderer Sensor)

Light

AVR-Tutorial: 7-Segment-Anzeige
AVR-GCC-Tutorial