Re: [Gumstix-users] u-boot device reconition questions...

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At 01:06 PM 2/24/2010, you wrote: 
<blockquote type=cite class=cite cite="">On Wed, Feb 24, 2010 at 11:14
AM, RayS &lt;ra...@bl...&gt; wrote: 
&gt; We have an Overo with Palo43 and LCD module; all is well and the
device 
&gt; boots and works fine.&nbsp; The LCD however has 4 wire SPI (ie with
CS) and is is 
&gt; not the best example for a driver for a read-only ADC module (no
CS). The 
&gt; main issue we're having is that the Gumstix only enables the SPI
clock 
&gt; (SCLK) if a device is recognized at boot. 
I think your expectations might be wrong.</blockquote> 
always possible! 
<blockquote type=cite class=cite cite="">The SPI clock is not
free-running.&nbsp; It is only driven during actual 
SPI transactions.</blockquote> 
SPI/SCLK can free run for the ADS1278 DEV (or
not) 
<a href="http://www.ti.com/lit/gpn/ads1278" eudora="autourl">
http://www.ti.com/lit/gpn/ads1278 
</a><blockquote type=cite class=cite cite="">If you intend to have
more than one device on the SPI bus you *must* 
have a chip select per device, otherwise the master has no way to 
indicate which slave should talk/listen. 
If you have only one device on SPI then you can get by with no chip
select.</blockquote> 
which is the current state of things 
<blockquote type=cite class=cite cite="">&gt; We're having a tough
time figuring 
&gt; out what we need to write a kernel (or user) driver that enables
SPI, or can 
&gt; assume SPI is enabled from boot.. 
SPI is enabled in the standard image, but you will of course need to 
write a kernel driver for the SPI chip you intend to use, and you
will 
also need to modify the overo board file in linux to enable that 
driver.</blockquote> 
working on that... 
<blockquote type=cite class=cite cite="">&gt; By observing the log
file of the booting when the touchscreen is mounted, 
&gt; u-boot seems to do device 
&gt; recognition. 
U-boot does nothing with SPI.&nbsp; The log messages you are referring
to 
are output by the linux kernel during the boot process. 
&gt; Before the log file shows &quot;remounting root fs&quot; (including
remounting of 
&gt; ads7846.c, which is the 
&gt; touchscreen driver), the log file shows &quot;booting&quot;, meaning
u-boot is 
&gt; running. 
&gt; It is during this &quot;booting&quot; that ADS7846 is detected on
SPI 1, Chip Select 
&gt; 0, or is not. 
&gt; It is detected when in board_overo.c the field .modalias =
&quot;ads7846&quot;. 
&gt; Without this field written in board-overo.c, the detection doesn't
happen. 
&gt; Once again, this detection is during &quot;booting&quot; as per the
log file. 
&gt; The log file prints messages that show detection or not. 
&gt; The exact words in these messages are not found with a search engine
on the 
&gt; computer, meaning 
&gt; we don't have the source code that generates them. 
&gt; So, where are they? 
They are in the linux ads7846 driver! 
<a href="http://www.sakoman.com/cgi-bin/gitweb.cgi?p=linux-omap-2.6.git;a=blob;f=drivers/input/touchscreen/ads7846.c;h=7cc9973241e51dcb88de2087b77c9526a4ed7666;hb=refs/heads/omap3-2.6.32" eudora="autourl">
http://www.sakoman.com/cgi-bin/gitweb.cgi?p=linux-omap-2.6.git;a=blob;f=drivers/input/touchscreen/ads7846.c;h=7cc9973241e51dcb88de2087b77c9526a4ed7666;hb=refs/heads/omap3-2.6.32</a>
 
&gt; u-boot also puts Chip Select to 0 on SPI 1 after it detects
ADS7846. 
&gt; Later-on, after &quot;remounting root fs&quot;, the file ads7846.c
(the touchscreen 
&gt; driver) takes over, detects ADS7846 
&gt; like u-boot did, does transmit and receive on the SPI bus when the
screen is 
&gt; touched, and maintains 
&gt; Chip Select to 0. 
U-boot does nothing with SPI.&nbsp; The log messages you are referring
to 
are output by the linux kernel during the boot process.</blockquote> 
thanks, we'll review 
 
Ray</body>
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