Backoff algorithm

Backoff algorithm

[Andrey Lukyanenko]

Hello Everyone,

I wanted to find implementation of backoff protocols for different platforms.
I tried to find it in various open-source drivers in linux-sources, madwifi and
stlc45xx. Everywhere I could only find some initialization of CWmax, CWmin, ...
but not the actual algorithm (something like, cw = min(cw<<1 + 1, cwmax) ),
except ath_rate sample/mistrel where the operation is used for "best
rate measurement"
as I understood.
Am I correct to assume that the protocol is implemented in firmwhere and there
is no open source driver which I could use to "play" directly with it?

Thanks in advance.

-- 
Best regards,
Andrey Lukyanenko.

Re: Backoff algorithm

[Johannes Berg]

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On Thu, 2009-12-17 at 16:10 +0200, Andrey Lukyanenko wrote:
> Hello Everyone,
> 
> I wanted to find implementation of backoff protocols for different platforms.
> I tried to find it in various open-source drivers in linux-sources, madwifi and
> stlc45xx. Everywhere I could only find some initialization of CWmax, CWmin, ...
> but not the actual algorithm (something like, cw = min(cw<<1 + 1, cwmax) ),
> except ath_rate sample/mistrel where the operation is used for "best
> rate measurement"
> as I understood.
> Am I correct to assume that the protocol is implemented in firmwhere and there
> is no open source driver which I could use to "play" directly with it?

Yes, basically. It's not something you can really implement in any
driver anyway as it's very timing sensitive.

ar9170 even has this in hardware, afaik, although you can of course play
with it in b43 firmware and/or ar9170 by influencing the value you give
the hw.

johannes

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Re: Backoff algorithm

[Andrey Lukyanenko]

Thanks a lot for your help.

I have found OpenFWWF project, which has open source firmware for Broadcom
chipsets. Unfortunately it does not support CTS/RTS, AP.
What do you mean by " influencing the value you give the hw"?
Are you talking about direct access to registers? How can I influence.
I have heard about tos-mac (TinyOS) which uses directly registers but it
is for sensors. Do you mean something similar?

In our group we have five ar5213 chips, I hope I can try to use it.

On Thu, Dec 17, 2009 at 4:54 PM, Johannes Berg
<johannes@sipsolutions.net> wrote:
> On Thu, 2009-12-17 at 16:10 +0200, Andrey Lukyanenko wrote:
>> Hello Everyone,
>>
>> I wanted to find implementation of backoff protocols for different platforms.
>> I tried to find it in various open-source drivers in linux-sources, madwifi and
>> stlc45xx. Everywhere I could only find some initialization of CWmax, CWmin, ...
>> but not the actual algorithm (something like, cw = min(cw<<1 + 1, cwmax) ),
>> except ath_rate sample/mistrel where the operation is used for "best
>> rate measurement"
>> as I understood.
>> Am I correct to assume that the protocol is implemented in firmwhere and there
>> is no open source driver which I could use to "play" directly with it?
>
> Yes, basically. It's not something you can really implement in any
> driver anyway as it's very timing sensitive.
>
> ar9170 even has this in hardware, afaik, although you can of course play
> with it in b43 firmware and/or ar9170 by influencing the value you give
> the hw.
>
> johannes
>



-- 
Best regards,
Andrey Lukyanenko.

Re: Backoff algorithm

[Johannes Berg]

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On Wed, 2009-12-23 at 14:28 +0200, Andrey Lukyanenko wrote:
> Thanks a lot for your help.
> 
> I have found OpenFWWF project, which has open source firmware for
> Broadcom
> chipsets. Unfortunately it does not support CTS/RTS, AP.
> What do you mean by " influencing the value you give the hw"?
> Are you talking about direct access to registers? How can I influence.
> I have heard about tos-mac (TinyOS) which uses directly registers but
> it
> is for sensors. Do you mean something similar?
> 
> In our group we have five ar5213 chips, I hope I can try to use it.

Umm, I don't think you understood what I said. I only mentioned ar9170
and broadcom devices...

johannes

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Re: Backoff algorithm

[Andrey Lukyanenko]

> Umm, I don't think you understood what I said. I only mentioned ar9170
> and broadcom devices...

Yes, I understood that you only meant ar9170 and b43. But what do you mean
by " influencing the value you give the hw"?
Firmware is not open source, afaik. How can I influence the values?

What I said about OpenFWWF and tos-mac are just some recent findings
about existing implementations of backoff scheme.

-- 
Best regards,
Andrey Lukyanenko.

Re: Backoff algorithm

[Johannes Berg]

On Wed, 2009-12-23 at 14:54 +0200, Andrey Lukyanenko wrote:
> > Umm, I don't think you understood what I said. I only mentioned
> ar9170
> > and broadcom devices...
> 
> Yes, I understood that you only meant ar9170 and b43. But what do you
> mean
> by " influencing the value you give the hw"?
> Firmware is not open source, afaik. How can I influence the values?

Well both b43 and ar9170 have open firmware. I don't know how to solve
your problem, and I'm not interested in it either -- I'm just trying to
give you pointers that may help. However, if you only have the hw you
do, then I don't know at all.

johannes

Re: Backoff algorithm

[Andrey Lukyanenko]

> Well both b43 and ar9170 have open firmware. I don't know how to solve
> your problem, and I'm not interested in it either -- I'm just trying to
> give you pointers that may help. However, if you only have the hw you
> do, then I don't know at all.

Yes, your are right. Acctually I already checked the source code of ar9170-fw
(I forgot about it, as I did not find what I was interested in it) and b43_4.5.
The second was a part of OpenFWWF project. The backoff code in b43 is
in few asm functions (right now easiest for me way to change, only need to
buy hw).

Thanks a lot, I am really appreciate your help.


-- 
Best regards,
Andrey Lukyanenko.