Re: [Flashforth-devel] Switching Endians -- swapbytes for FF18

[Mikael N. <mik...@pp...>]

That's great Craig, but can you spot the bug in your code ?

It can also be done with temp registers, since FF has alot of interrupt 
safe temp registers, Tp(fsr1) in this case.

Swapbytes is called '><' in the Atmega FF. It was needed there to 
manipulate return addresses.

: ><
  [ Sminus, w, a, movf,    ]
  [ Srw, Tp,         movff,   ]
  [ Splus,         a, movwf, ]
  [ Tp,   Srw,       movff,   ]
;

BR Mike

On 03/27/2014 08:18 PM, craig bair wrote:
> I needed to swap bytes to send to another machine, so I implamented 
> one of my favorite tricks from "back in the day" when I was learning 
> MACRO-11 on the college PDP-11/40...  Swapping register contents 
> without auxiliary storage.  Mike's made it easy for us in the Pic18-s, 
> probably the rest of the chips, too.
>
> swapbytes ( xy -- yx ) \ reverses byte order on Top-Of-Stack
>
> craig bair
>
> ---------------
>
> \ Reverse ENDIAN-ness of 16-bit on Top Of Stack
> \ i.e. Swap Bytes
> \ ...minimalist approach, no temp storage loc
> \
> \ needed constants (could be hardwired into code
> $ffe9 constant fsr0    \ ; 0xFE9 FSR0L
> \ $ffea constant fsr0h    \ ; 0xFEA FSR0H
> $ffef constant indf0    \ INDirect-by-FSR0 FileRegister
> 1 constant f,     \ Destination File
> \
> \ needed assembler constructor
> : as2 ( opcode "name" -- ) ( f a -- )
>   co:
>   does> rot ic, or ic, ;
> \
> \ needed assembler instructions
> $04 as3 decf,           ( f d a -- )
> $28 as3 incf,           ( f d a -- )
> $18 as3 xorwf,          ( f d a -- )
> $6e as2 movwf,          ( f a -- )
> \
> \ actual word
> : swapbytes    ( xy -- yx ) \ swap Hi:Lo bytes on Top of Stack
>    [ indf0 w, a, movf,  ]
>    [ fsr0  f, a, decf,  ]
>    [ indf0 f, a, xorwf, ]
>    [ indf0 w, a, xorwf, ]
>    [ indf0 f, a, xorwf, ]
>    [ fsr0  f, a, incf,  ]
>    [ indf0 a, movwf,    ]
> ;
>
> ...averaging may or may not help clarify data.
>        If Bill Gates walks into a bar,
>    the average patron becomes a millionaire...
>
>
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>
>
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