linux-kernel - Re: w1_ds2408 linux driver

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Message-ID: <47BBCF14-C7BC-4C35-826A-52A50EFB8B4B@sonatest.com>
Date:	Thu, 7 Mar 2013 20:09:14 +0000
From:	Jean-Francois Dagenais <DagenaisJ@...atest.com>
To:	Olivier KSIKES <olivier@...rods.com>
CC:	open list <linux-kernel@...r.kernel.org>
Subject: Re: w1_ds2408 linux driver


On 2013-02-19, at 9:44 AM, Olivier KSIKES wrote:

> Dear Mr Dagenais,
> 
> I have just tried your w1-ds2408 linux driver on a TP link mini router running openwrt with w1-gpio. I was able to successfully update a 2408 outputs by writing a byte to the /output file.
> However, I would like to drive an LCD screen, and this method seems limited to 3/4 chars per second.
> 
> I had little more luck driving the 2408 thru the generic w1 driver (using the rw file), where I reached around 25 bytes/s.
> This is however far from the actual 1wire bus capabilities.
> 
> Thus, I'm wondering if there is a faster way to output a series of bytes to the 2408 using your driver?
> Is there any doc available apart from w1_ds2408.c comments?
> 
> With best regards and congratulations for your great work,
> 
> Olivier Ksikes

Here are my test results.

I have a simple main() that opens the /sys/bus/w1/devices/29-0000000xyz/output
file and keeps it open.

I sweep from 0 to 255 in a tight loop that simply does

   for (int i=0; i <= 1024; ++i) {
      file.putChar(i);
      file.seek(0);
   }
   return 0;

I invoke this using "time" and do 1024/timespent to get:
Current  driver (w/read-back ): ~48 chars/seconds
Improved driver (wo/read-back): ~98 chars/seconds

patch will follow...

Cheers.




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