Re: Dallas one - wire on avr

Thanks - Seems that using the code from Leon the toggle now takes 500 ns - and a nop can push it out by 250 ns. I'm using SwiftX regular- no optimizer - so thats probably why it was slow when I started out.

Great Stuff - thanks again.
Matthew Karas

PS - when I'm finished writing one wire interface code - would anyone want to see it up on the forth online and interactive site?

"Leon Wagner" <leon_at_forth.com> wrote:

>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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