asm Statement

mikroBasic PRO for dsPIC30/33 and PIC24 allows embedding assembly in the source code by means of the asm statement. Note that you cannot use numerals as absolute addresses for register variables in assembly instructions. You may use symbolic names instead (listing will display these names as well as addresses).

You can group assembly instructions with the asm keyword:

asm
   block of assembly instructions
end asm

The only types whose name remains the same in asm as it is in the mikroBasic PRO for dsPIC30/33 and PIC24 are registers, e.g. INTCON, PORTB, WREG, GIE, etc.

mikroBasic PRO for dsPIC30/33 and PIC24 comments are allowed in embedded assembly code.

Accessing variables

Depending on the place of declaration, accessing a variable can be done in several ways :

Accessing global variable :
1. If declared under implementation section (visible only in the file where it was declared) : <source_file_name>_<variable_name>.
2. If declared in the interface section (visible throughout the whole project) : _<variable_name>.
3. If accessing registers (declared through register, rx or sfr specifiers, visible throughout the whole project) : <variable_name>.
Accessing local variable : <routine_name>_<variable_name>.
Accessing routine parameter : FARG_<routine_name>_<variable_name>.

Here is an example of using asm instructions :

program asm_example

dim myvar as word absolute 0x2678
dim myvar1 as longword
const msg = "Hello" org 0x1234

sub procedure proc() org 0x2346
  asm
    nop
  end asm
end sub

main :
  myvar = 5
  myvar1 = 0xABCD1234

  asm
      MOV _myvar, w0                      ; move myvar to W0
      nop
      MOV #6, W0                          ; move literal 6 to W0
      MOV W0, _myvar                      ; move contents of W0 to myvar
      MOV #lo_addr(_myvar), w1            ; retrieve low address word of _myvar and move it to W1 (0x2678 -> W1)
      MOV #hi_addr(_myvar), W1            ; retrieve high address word of _myvar and move it to W1 (0x0000 -> W1)
      MOV #lo_addr(_proc), W0             ; retrieve hi address byte of routine proc and move it to W0 (0x0001 -> W1)
      MOV #lo_addr(_msg), W0              ; retrieve low address word of constant msg and move it to W0 (0x3652 -> W1)
      MOV _myvar1+2, w0                   ; accessing hi word of myvar1 variable and move it to W1 (0xABCD -> W1)
  end asm

end.

Asm code and SSA optimization

If asm code is mixed with the Basic code, keep in mind that the generated code can substantially differ when SSA optimization option is enabled or disabled.
This is due to the fact that SSA optimization uses certain working registers to store routine parameters (W10-W13), rather than storing them onto the function frame.

Because of this, user must be very careful when writing asm code as existing values in the working registers used by SSA optimization can be overwritten.
To avoid this, it is recommended that user includes desired asm code in a separate routine.

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