From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ned Forrester Subject: Re: PXA270 SSP DMA Corruption Date: Wed, 12 Nov 2008 22:19:49 -0500 Message-ID: <491B9CD5.3030908@whoi.edu> References: <20080211174339.73ca7ed5.merrij3@rpi.edu> <47B0D9A4.6080104@whoi.edu> <20081107184819.54baa679.merrij3@rpi.edu> <491B6249.7070407@whoi.edu> <20081112213403.402948b9.merrij3@rpi.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: spi-devel To: "J. Scott Merritt" Return-path: In-Reply-To: <20081112213403.402948b9.merrij3-IL7dBOYR4Vg@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: spi-devel-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-spi.vger.kernel.org J. Scott Merritt wrote: > On Wed, 12 Nov 2008 18:10:01 -0500 > It appears that the timeout is computed based upon the "Peripheral Clock > frequency" on the PXA270 - which would appear to be 312Mhz, (or something > divided down from there). If it is 312Mhz, then for my SSP speed of > 300K, I guess I need something around 10,000. It says "peripheral clock frequency" without ever defining that phrase (at least in the 1/2006 version of the developer's manual). Oddly on PXA255 this frequency appears to be runclock/4 = 99.5MHz for a 400MHz machine. I bet it is not as high as 312MHz, but you can measure it by setting very long times, forcing the timeout (no tx data in pio mode, I think), and perhaps using GPIO probes to trigger a scope. I did something like that on my system. It would sure be nice to know the answer to that, as no one using PXA270 has ever answered the question. > Table 8-4 in my PXA manual is titled "TFT and RFT values with possible > DMA Burst Sizes" ... for 8 bit data, it says ... for TFT > 7 > "Do not use DMA" ... Am I misinterpreting this ? I -think- that means > that 8/8 is not a good choice ... The table you refer to lists the values loaded into the TFT and RFT bit fields, which are the desired threshold-1. The values passed to pxa2xx_spi are the desired thresholds, so TFT>7 is the same as threshold>8. > With respect to the pxa2xx_spi patch, please proceed - I will certainly > not attempt to generate one myself. I'll get something out in the next couple of days. -- Ned Forrester nforrester-/d+BM93fTQY@public.gmane.org Oceanographic Systems Lab 508-289-2226 Applied Ocean Physics and Engineering Dept. Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA http://www.whoi.edu/sbl/liteSite.do?litesiteid=7212 http://www.whoi.edu/hpb/Site.do?id=1532 http://www.whoi.edu/page.do?pid=10079 ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/