From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-out.m-online.net (mail-out.m-online.net [212.18.0.9]) by ozlabs.org (Postfix) with ESMTP id EEDF8679E7 for ; Wed, 5 Jul 2006 05:49:40 +1000 (EST) To: "hubert.loewenguth" From: Wolfgang Denk Subject: Re: what is the MPC8260 spi maximum rate ? Mime-version: 1.0 Content-type: text/plain; charset=ISO-8859-1 In-reply-to: Your message of "Tue, 04 Jul 2006 10:12:19 +0200." <44AA22E3.3050701@thales-bm.com> Date: Tue, 04 Jul 2006 21:49:37 +0200 Sender: wd@denx.de Message-Id: <20060704194937.021BA353A1D@atlas.denx.de> Cc: linuxppc-embedded@ozlabs.org List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hello, in message <44AA22E3.3050701@thales-bm.com> you wrote: > > It is written in MPC8260 documentation (SPI chapter) : " The maximum > sustained data rate that the SPI supports is SYSTEMCLK/50. However the > spi can transfer a single character at much higher rates (SYSTEMCLK/4 in > master mode)". > > My really stupid question is ...... what is "SYSTEMCLK" ??????? > is it the BRG_CLK ? the CPM_CLK or the CPU_CLK ???? The performance-limiting factor is the CPM, so it's most probably the CPM clock. > This question is quite stupid but very important for me in order to know > if that controller permit to exchange data with one of our extention > board at 1.2 MHz. Keep in mind that SPI is implemented in software on the CPM, and that it's running at very low priority. All calculations assume an otherise unloaded CPM - but if you add load to the CPM, things will change. We haven't run specific measurements on the 8260, but on the MPC860 we ran into a *lot* of ugly SPI problems when the CPM load got higher, missing interrupts etc. being just one of the issues. At this time, Motorola added a note to their FAQ base, which stetd pretty clear that SPI was "not designed for high-bandwidth data communi- cations". Best regards, Wolfgang Denk -- Software Engineering: Embedded and Realtime Systems, Embedded Linux Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de Due to lack of disk space, this fortune database has been discontinued.