BeagleBone Black

[Tim Kientzle]

On Apr 28, 2013, at 2:37 AM, Iain Young wrote:
> On 28/04/13 08:13, Tim Kientzle wrote:
> 
>> The 4-pin adapter I got from Adafruit for use with Raspberry Pi seems
>> to work just fine, though the CircuitCo documentation has the instructions
>> wrong.  It should be:
>>    Black => Pin 1
>>    Green => Pin 4
>>    White => Pin 5
> 
> Hurm, I wonder what the other 3 pins are used for. They seem to be
> undocumented in the SRM

I believe they're unconnected.  They're only there for compatibility
with the common FTDI TTL-232R-3v3 USB-to-serial
adapter that has a 6-pin connector.

>> Harumph.  Looks like it always boots initially from the eMMC and
>> U-Boot then looks at the boot switch to decide whether to continue
>> from eMMC or uSD.
> 
> This would appear to be the default behaviour, but can be over-ridden
> if I read the SRM correctly. For a one off force to uSD boot, hold down
> the "boot" button". See Page 57 of the SRM

Tried that, but from watching the serial console, it's still
loading U-Boot from the eMMC.  It's U-Boot that actually looks
at that pin (there are some messages on the serial console
about U-Boot inspecting a GPIO pin).

>> This sucks:  the U-Boot on the eMMC doesn't have ELF support
>> nor API support so can't load and boot ubldr.
>> 
>> Short version:  The existing FreeBSD images for BeagleBone
>> won't work as-is.  At a minimum, we'll have to replace the U-Boot
>> on the eMMC with one that has ELF and API enabled.    I guess
>> I'll be spending more quality time with U-Boot.  :-/
> 
> Or wipe the eMMC. In that case, then it appears it boots off
> the uSD card next.

Yep.   Or replace U-Boot on the eMMC, which is what I was
hoping to look into today.

The model that the BeagleBone seems to use for "installing a new OS"
is basically a two-drive model (in essence, the micro-SD is drive 0 and
the eMMC is drive 1):
   * Download an "installer image" to micro-SD.
   * Boot from that micro-SD/drive 0.
   * That "installer" copies the OS onto drive 1/eMMC
   * Reboot from eMMC.

Tim