AVRGCC Syntax

A quick guide to some of the C syntax that is specific to avr-gcc.

For more examples, see Harold Leitner's Appplication Notes

• Data Types - it is very important to keep track of how big your variables are. The following are defined in inttypes.h. When used in your program, they are created in RAM.
  
  

  Data Type	Length (bits | bytes)	Value Range
  Uint8_t	8 | 1	0 to 255
  Int8_t	8 | 1	-128 to 127
  Uint16_t	16 | 2	0 to 65535
  Int16_t	16 | 2	-32768 to 32767
  Uint32_t	32 | 4	0 to 4294967295
  Int32_t	32 | 4	-2147483648 to 2147483647
  Uint64_t	64 | 8	0 to 1.8*1019
  Int64_t	64 | 8	-9.2*1018 to 9.2*1018

  
  
  
• There is another set of data types defined in the AVRLIB in global.h, that sometimes easier to use. You will find them more commonly in our demo programs.
  
  

  Data Type	Length (bits | bytes)	Value Range
  u08	8 | 1	0 to 255
  s08	8 | 1	-128 to 127
  u16	16 | 2	0 to 65535
  s16	16 | 2	-32768 to 32767
  u32	32 | 4	0 to 4294967295
  s32	32 | 4	-2147483648 to 2147483647
  u64	64 | 8	0 to 1.8*1019
  s64	64 | 8	-9.2*1018 to 9.2*1018

  
  
  
• Setting and Clearing Bits - remember that setting a bit is setting it high or to 1, and clearing a bit is making it low or 0.
  • void sbi(u08 register, u08 bit)
    
    Sets a bit in a register. For example, to set the 0th bit of Port D, you can use:
    
    sbi(PORTD,0);
    
    or
    
    sbi(PORTD,PD0);
    
    or
    
    sbi(PORTD,PIND0);
  
  
  
  • void cbi(u08 register, u08 bit)
    
    Clears a bit in a register. For example, to clear the 2nd bit of Port B, you can use:
    
    cbi(PORTB,2);
    etc...
    
  
  
  
• Writing to and Reading from registers
  • void outb(u08 port, u08 val)
    
    Writes the byte val to a register. Note! In the Leitner documentation and some old demos you may see void outp(u08 val, u08 port). This syntax is being phased out so try to avoid it.
    
    outb(PORTD,0x0F);
    
    would write 0x0F or 00001111 to Port D.
    
    
  • u08 inb(u08 port)
    
    Returns a byte containing the value in a register. As with outp / outb, you may sometimes see inp, but try to avoid using it.

    u08 status;
    status = inb(PIND);
    

    is the correct read the value from the Port D pins into the variable status.
    
    Note the difference between PIND and PORTD. PIND is read-only and gives the value at the physical pins on Port D. PORTD is a read/write register that is normally used for writing. You cannot use:

    status = inb(PORTD); // DON'T DO THIS IF YOU WANT TO READ THE PORT D PINS
    

    For more details, and descriptions of these registers, please see page 111 in the I/O section of the Mega163 Spec.

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Send comments about this page to gurevich@ccrma.stanford.edu Last modified: Thu Oct 3 18:31:16 PDT 2002