Date: Mon, 3 Dec 2012 09:17:31 -0700 From: Warner Losh <imp@bsdimp.com> To: "Daisuke Aoyama" <aoyama@peach.ne.jp> Cc: freebsd-arm@freebsd.org, Ralf.Wenk@hs-karlsruhe.de Subject: Re: FreeBSD on Raspberry Pi 512MB (with U-Boot + ubldr) Message-ID: <18DB98C9-66D9-4B00-989A-156F21E9981C@bsdimp.com> In-Reply-To: <B3D30A45699E443399D7CB112082356B@ad.peach.ne.jp> References: <3988C1622A974F19A9D3888F0334FF10@ad.peach.ne.jp> <50B8058C.9030909@bluezbox.com> <E1TfWh4-00BZ82-Is@smtp.hs-karlsruhe.de> <B3D30A45699E443399D7CB112082356B@ad.peach.ne.jp>
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On Dec 3, 2012, at 7:51 AM, Daisuke Aoyama wrote: >>>> BTW, SDHCI is not yet stable? >>>=20 >>> There is one issue with setting SDHCI clock. I'll commit fix later = today. >>=20 >>=20 >> I like to share some information about the SD card reading speed. >>=20 >> While exchanging the old boot sequence with then new one I once = booted >> with the new boot sequence but without an /boot/loader.rc file. >>=20 >> The reading speed achieved with >> dd if=3D/dev/mmcsd0 of=3D/dev/null bs=3D1m count=3D100 >> from the SD card was 10 Mbyte/sec. >>=20 >> After creating the file with "echo 'fdt addr 0x100' > = /boot/loader.rc" >> and rebooting the reading speed achieved from the SD card was down to >> 2.8 Mbyte/sec. >>=20 >> Although the SDHCI frequency was shown on the second boot as double = high as >> on the first (100MHz versus 50MHz) the reading speed was much lower. >> I think the cause was the mmcsd bus bit width which was reported as 4 = at >> the first and as 1 at the second boot. >=20 > At this time, it must be 50. if use 100MHz, some cards cant be used = anymore. > Howerver, probably 4bit transfer is OK. 33MHz is the top speed for SD cards. There's an extension to make them = go as fast as 50MHz. Most SD cards cope at 50MHz without enabling the = extension and even more when enabled. The current common code tries to = enable things properly, but relies on the host bridge adapter driver to = set the clock properly... There may be some cruft here left over from = the early Atmel legacy where the datasheet gave somewhat aggressive = advise.. 100MHz at one bit is 100Mbps. 50MHz 4 bit is 200Mbps. I gotta get a pi to play around with this :) Warner=
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