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ASAVR Assembler

AVR ASSEMBLER NOTES 

     The AVR series of processors uses a non  unified addressing
scheme:  the instruction addressing is 1 per  instruction  word,
each  instruction uses 2 bytes of memory.  The processor data is
addressed as 1 per byte of data.  To properly address  the  pro-
gram/data spaces you, the programmer, must seperate your program
and data into seperate code and data areas.  The  data  area  is
addressed  as 1 per byte and the code area is addressed as 1 per
instruction.  

     The assembler/linker processes the instruction code so that
the linker will output 2 bytes for each instruction  word.   The
instruction  word  address  will  be  the  file  encoded address
divided by 2.  


PROCESSOR SPECIFIC DIRECTIVES 

     The  normal  PC relative addressing is -2047 to +2048 rela-
tive to the current PC.  For a processor with less than 4K words
of program space the AVR relative jump/call can access any loca-
tion due to address wrap around.  

     The  ASAVR  cross  assembler has one (1) processor specific
assembler directive which tells the assembler that the  AVR  has
4K words or less of program space.  

        .avr_4k   0     Normal PC Relative addressing
        .avr_4k   1     AVR with <= 4K of Memory

     The remaining processor specific directives specify the AVR
processor type.  

        .AT90SXXXX
        .AT90S1200
        .AT90S2313
        .AT90S2323
        .AT90S2343
        .AT90S2333
        .AT90S4433
        .AT90S4414
        .AT90S4434
        .AT90S8515
        .AT90C8534
        .AT90S8535
        .ATmega103
        .ATmega603
        .ATmega161
        .ATmega163
        .ATtiny10
        .ATtiny11
        .ATtiny12
        .ATtiny15
        .ATtiny22
        .ATtiny28

   A  file, avr.sfr, contains definitions for the Spepcial Func-
tion Registers for all the defined processors.  Edit the file to
make  your  selection of processor and then .include the file at
the beginning of your assembler file.  


The .__.CPU.  Variable 

   The value of the pre-defined symbol '.__.CPU.' corresponds to
the selected processor type.  The default value is 0 which  cor-
responds  to  the  default  processor type.  The following table
lists the processor types and associated values  for  the  ASAVR
assembler:  

        Processor Type            .__.CPU. Value
        --------------            --------------
         Undefined                       0
         AT90SXXXX (User Defined)        1
         AT90S1200                       2
         AT90S2313                       3
         AT90S2323                       4
         AT90S2343                       5
         AT90S2333                       6
         AT90S4433                       7
         AT90S4414                       8
         AT90S4434                       9
         AT90S8515                      10
         AT90C8534                      11
         AT90S8535                      12
         ATmega103                      13
         ATmega603                      14
         ATmega161                      15
         ATmega163                      16
         ATtiny10                       17
         ATtiny11                       18
         ATtiny12                       19
         ATtiny15                       20
         ATtiny22                       21
         ATtiny28                       22


   The  variable  '.__.CPU.'  is by default defined as local and
will not be output to the created .rel file.  The assembler com-
mand line options -g or -a will not cause the local symbol to be
output to the created .rel file.  

   The  assembler  .globl  directive  may  be used to change the
variable type to global causing its definition to be  output  to
the  .rel file.  The inclusion of the definition of the variable
'.__.CPU.' might be a useful means of validating that seperately
assembled  files have been compiled for the same processor type.
The linker will report an error for variables with multiple  non
equal definitions.  

AVR REGISTER SET 

The following is a list of the AVR registers used by ASAVR:  

        r0-r31  -       8-bit registers
        x       -       index register (x = r27:r26)
        y       -       index register (y = r29:r28)
        z       -       index register (z = r31:r30)


AVR ADDRESSING MODES 

   The designation [] refers  to  a  required addressing  mode
argument.   The  following  list specifies the format for each
addressing mode supported by ASAVR:  

        #data           immediate data

        expr            expression

        Rd              destination register (0-31)

        Rd,Rs           destination register (0-31)
                        source register (0-31)

        Rd,#data        destination register (0-31)
                        immediate data

        addr            address

        addr,Rs         destination address
                        source register

        Rd,addr         destination register
                        source address

        Rs,b            source register
                        bit position

        Rd,b            destination register
                        bit position

        A               an I/O register (0-31)

        A,b             an I/O register (0-31)
                        bit position

        A,Rs            source register to
                        output register

        Rd,A            input register to
                        destination register

        Rd,X            load indirect
        Rd,Y
        Rd,Z

        Rd,-X           load indirect pre-decrement
        Rd,-Y
        Rd,-Z

        Rd,X+           load indirect post-increment
        Rd,Y+
        Rd,Z+

        Rd,Z+Q          load indirect with displacement

        X,Rs            store indirect
        Y,Rs
        Z,Rs

        -X,Rs           store indirect pre-decrement
        -Y,Rs
        -Z,Rs

        X+,Rs           store indirect post increment
        Y+,Rs
        Z+,Rs

        Z+Q,Rs          store indirect with displacement

        label           branch label

The  terms  data, expr, displacement, bit position, A, and label
may be expressions.  

AVR INSTRUCTION SET

     Note  that  not  all  instructions are available with every
processor type.  Not all addressing modes are valid  with  every
instruction,  refer to the AVR technical data for valid instruc-
tions and modes.  


AVR Arithmetic and Logical Instructions 

        add     Rd,Rs           adc     Rd,Rs
        adiw    Rd,#data        sub     Rd,Rs
        subi    Rd,#data        sbc     Rd,Rs
        sbci    Rd,#data        sbiw    Rd,#data
        and     Rd,Rs           andi    Rd,#data
        or      Rd,Rs           ori     Rd,#data
        cp      Rd,Rs           eor     Rd,Rs
        cpi     Rd,#data        cpc     Rd,Rs
        cbr     Rd,#data        sbr     Rd,#data
        clr     Rd              com     Rd
        dec     Rd              inc     Rd
        neg     Rd              ser     Rd
        tst     Rd
        mul     Rd,Rs           fmul    Rd,Rs
        muls    Rd,Rs           fmuls   Rd,Rs
        mulsu   Rd,Rs           fmulsu  Rd,Rs


AVR Bit and Bit-Test Instructions 

        lsl     Rd              lsr     Rd
        rol     Rd              ror     Rd
        asr     Rd              swap    Rd
        bset    b               bclr    b
        sbi     A,b             cbi     A,b
        bst     Rs,b            bld     Rd,b
        sec                     sez
        sen                     sev
        ses                     seh
        set                     sei
        clc                     clz
        cln                     clv
        cls                     clh
        clt                     cli
        nop                     sleep
        wdr


AVR Skip on Test Instructions 

        cpse    Rd,Rs
        sbrc    Rs,b            sbrs    Rs,b
        sbic    A,b             sbis    A,b


AVR Jump/Call/Return Instructions 

        jmp     addr            rjmp    addr
        ijmp                    eijmp
        call    addr            rcall   addr
        icall                   eicall
        ret                     reti


AVR Short Branch Instructions 

        brcc    label           brcs    label
        breq    label           brge    label
        brhc    label           brhs    label
        brid    label           brie    label
        brlo    label           brlt    label
        brmi    label           brne    label
        brpl    label           brsh    label
        brtc    label           brts    label
        brvc    label           brvs    label


AVR Short Branch Instructions with Bit Test 

        brbc    b,label         brbs    b,label


AVR Data Transfer Instructions 

        mov     Rd,Rs           movw    Rd,Rs
        ldi     Rd,#data
        ld      []              st      []
        ldd     []              std     []
        lds     Rd,addr         sts     addr,Rs
        lpm     []              elpm    []
        spm
        push    Rs              pop     Rd
        in      Rd,A            out     A,Rs

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Last Updated: January 2019