Date: Fri, 6 Jan 2017 12:37:19 -0200 From: "Dr. Rolf Jansen" <rj@obsigna.com> To: freebsd-arm@freebsd.org Subject: BeagleBone Black MMC ordering clashes Message-ID: <7D750433-59FC-4999-AC24-041683E17310@obsigna.com>
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The BeagleBone Black comes with 2 MMC facilities, one built-in (internal =
4 GB) and one provided by a removable SD card. For unknown reasons the =
BBB defined on the removable SD card to be MMC0 and the internal flash =
memory is MMC0.
1) In the first go, I dd'd the FreeBSD-12 BBB snapshot (20161221) onto =
a SD card and I was able to start the device from that card. gpart =
showed me that the device identifier of the SD card is mmcsd0 and that =
of the internal flash memory is mmcsd1. OK, that matches the already =
mentioned definitions.
2) Now, I destroyed the partition of the internal mmcsd1 and created a =
new one:
=3D> 63 7552961 mmcsd1 MBR (3.6G)
63 8129 - free - (4.0M)
8192 8192 1 fat32 [active] (4.0M)
16384 7536640 2 freebsd (3.6G)
=3D> 0 7536640 mmcsd1s2 BSD (3.6G)
0 7536640 1 freebsd-ufs (3.6G)
3) I copied over the contents of /boot/msdos from the external SD card =
to the msdosfs on mmcsd1s1 and I installed the FreeBSD 12 snapshot on =
mmcsd1s1a. Restarting the device from the internal flash and no external =
SD inserted with FreeBSD 12-CURRENT works well at the first glance.
4) However, the internal flash got now the device identifier mmcsd0:
...
mmc0: No compatible cards found on bus
...
mmcsd0: 4GB <MMCHC MMC04G 5.8 SN 82390DEC MFG 11/1998 by 112 0x0000> =
at mmc1 48.0MHz/8bit/65535-block
...
I know, this is how FreeBSD deals with the device numbering, i.e. serial =
numbers starting at zero without particular meaning, and I know that we =
should not rely on the number ordering.
But it seems that the MMC device driver does cont on the external SD =
card is at MMC0 when I insert it into the BBB once it has been started =
from the internal flash. It seems to insist to assign the device ID =
mmcsd0, which results in the device ordering clash because mmcsd0 has =
been assigned to the internal flash at MMC1 (s. above).
In the moment, I can have both flash device active at the same time only =
when I start the BBB from the external SD.
I would be glad to hear suggestions on how to deal with the issue. At =
the end of the day, I want to start the device from the mostly static OS =
file system on the internal flash and keep the volatile data on the =
external SD.
Best regards
Rolf
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