Re: Class4 / Class 10 SD cards on NetBSD

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Mon, Oct 26, 2015 at 06:28:42PM +0000, Ottavio Caruso wrote:
> Hello,
> 
> apparently on my Thinkpad X61 the sd card reader is attached to the
> PCI interface, not the USB hub
> 
> bash-4.3$ dmesg|grep sdh
> sdhc0 at pci3 dev 0 function 2: vendor 0x1180 product 0x0822 (rev. 0x21)
> sdhc0: interrupting at ioapic0 pin 18
> sdhc0: SD Host Specification 1.0, rev.4
> sdhc0: using DMA transfer
> sdmmc0 at sdhc0 slot 0
> 
> I am not sure how this plays with NetBSD. Would it make any difference
> in speed if I use a class 10 vs a class 4 SD card?
 
My X60 has a vendor 0x1180 product 0x0552 (rev. 0x09).  Speed class is
a certified minimum for sequential write speed.  Assuming the host
interface can keep up, a faster card is going to be faster.  Note that
these old machines probably don't support any of the UHS signaling
modes.

> And I must have read somewhere (maybe a forum) that *BSD cannot boot
> from an SD card. Please tell me it's not true. (Well, I know it's
> possible on the Raspberry, but on the PC?)

NetBSD/x86 can boot from pretty much any device you could run DOS from.

The BIOS on my X60 does not have a BIOS driver for the SDHCI, thus it
can not be booted from.  My EeePC (701 and 1215T) connect the SD card
via a USB-MSC chip, and as their BIOS (like most modern BIOSes) has
USB-MSC drivers the SD card is bootable, just like any other flash
drive.

(SeaBIOS is the only BIOS I am aware of that has SDHCI drivers, but I
am not sure if the driver has been validated on many non-emulated
SDHCI chips.  And you have to be running a VM or coreboot to run SeaBIOS
anyway.)

	Jonathan Kollasch