From: Wolfgang Denk <wd@denx.de>
To: "hubert.loewenguth" <hubert.loewenguth@thales-bm.com>
Cc: linuxppc-embedded@ozlabs.org
Subject: Re: what is the MPC8260 spi maximum rate ?
Date: Tue, 04 Jul 2006 21:49:37 +0200 [thread overview]
Message-ID: <20060704194937.021BA353A1D@atlas.denx.de> (raw)
In-Reply-To: Your message of "Tue, 04 Jul 2006 10:12:19 +0200." <44AA22E3.3050701@thales-bm.com>
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.
prev parent reply other threads:[~2006-07-04 19:49 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-07-04 8:12 what is the MPC8260 spi maximum rate ? hubert.loewenguth
2006-07-04 19:49 ` Wolfgang Denk [this message]
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