Re: Dallas one - wire on avr

Definitly write this in assembler. The bit-level I/O instructions (SBI and
CBI) on the AVR are exactly what you need. Here's all the code needed to
toggle bit 0 of Port A:

CODE TOGGLE
    0 PORTA SBI 0 PORTA CBI
   RET END-CODE

Note: There's no "interpreter overhead" inside a SwiftX/AVR definition.

: TOGGLE FF PORTA C! 0 PORTA C! ;

SEE TOGGLE

18F0 FF R16 LDI 0FEF
18F2 R16 1B OUT 0BBB
18F4 0 R16 LDI 00E0
18F6 R16 1B OUT 0BBB
18F8 RET 0895

The above example is using SwiftX Pro with the code optimizer turned on. If
you turn off the optimizer (or are using the Lite version which doesn't have
the code optimizer), you would get this:

18FA (LITERAL) RCALL 8FD3
18FC LITERAL FF FF00
18FE (LITERAL) RCALL 8DD3
1900 LITERAL 3B 3B00
1902 C! RCALL 88D5
1904 (LITERAL) RCALL 8AD3
1906 LITERAL 0 0000
1908 (LITERAL) RCALL 88D3
190A LITERAL 3B 3B00
190C C! RJMP 83C5

As you can see, these literal sequences optimize very nicely on the AVR.

> The problem I'm having so far is that the fastest I can toggle a
> bit with forth on the atmega16 running at 4MHz is only 25 uSec.
> I need to toggle bits much faster than that. So far the code I'm
> using looks like
>
> :TOGGLE
> FF PORTA C!
> 00 PORTA C!
> ;
>
> Is there a divide down for the avr's data bus? Or is the
> interpreter really taking that long to execute the code?
>
> How much faster would
> :TOGGLE
> 00 PORTA FF PORTA C! C!
> ;
> be?
>
> Should I just write these bits in assembler?
>
> Thanks,
> Matthew Karas
>
> Frank Boon <fboon_at_runbox.com> wrote:
>
> >I am implementing a 1-wire master with a DS2480B, because it can control
> >the slew-rates.
> >Not fully implented yet...
> >
> >Frank Boon,
> >Metatronics
> >
> >Matthew Karas wrote:
> >
> >>Has anyone implemented one wire routines using Atmel's avr318 appnote?
> >>
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Received on Thu Nov 18 2004 - 07:50:29 PST