Date: Thu, 23 Feb 2012 10:57:40 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Patrick Kelsey <kelsey@ieee.org> Cc: freebsd-mips@freebsd.org Subject: Re: ar71xx SPI speed Message-ID: <CAJ-VmokkbJVV65xKEqdxiN8edkajBDc42iR9rd2uH1WZrnnoxA@mail.gmail.com> In-Reply-To: <CAD44qMX9ndkmdmT4Ba-7vJetJDv1HkhDpoFXUHYFT-cfPW4c5g@mail.gmail.com> References: <CAD44qMX9ndkmdmT4Ba-7vJetJDv1HkhDpoFXUHYFT-cfPW4c5g@mail.gmail.com>
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Hi, If you take a look at the source code, IIRC reads are done via the hardware but the writes are done via bit banging. Are you looking at SPI read, SPI write, or a mix of both? You can increase the hardware SPI clock by correct fondling of the right registers but I haven't got any spare cycles to go grovelling through the AR7100 datasheet at the moment. Sorry. Poke me in a few days. Adrian On 21 February 2012 14:22, Patrick Kelsey <kelsey@ieee.org> wrote: > Hi, > > I've been doing some SPI-related work on an AR7161-based board (MikroTik > Routerboard RB450G, CPU @ 680 MHz, DDR @ 340 MHz, AHB @ 170 MHz), and I'v= e > noticed, via both software cyclecount and logic analyzer traces, that the > SPI bus clock tops out in the neighborhood of 7 MHz or so. =A0I can get a > little more performance out of it if I manually unroll/debranch the loop = in > ar71xx_spi_txrx, but not terribly much. =A0The (closed source) boot loade= r > for this board manages something in the neighborhood of 8.5 MHz (perhaps > due to not going through a bus abstraction layer in its code). =A08MHz-is= h > does seem a bit lethargic for an SoC with otherwise fast moving parts, bu= t > I don't have any technical documentation on which to base a meaningful > expectation. > > I'm wondering if anyone has had any experience with this SPI controller > that either corroborates or contradicts this apparent speed limit. > > Thanks, > Patrick > _______________________________________________ > freebsd-mips@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-mips > To unsubscribe, send any mail to "freebsd-mips-unsubscribe@freebsd.org"
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