Re: [LUG] Pi mystery

[Julian Hall <linux@xxxxxxxxxxxx>]

On 25/11/13 21:18, Gordon Henderson wrote:
> On Mon, 25 Nov 2013, Philip Hudson wrote:
>
> > My son's Raspberry Pi rev B boots from its 4GB SD card (Raspbian) only
> > intermittently. It was running fine at home before we shut down 
> > (properly)
> > and disconnected it to take it to Exeter. At Exeter, to our not very 
> > great
> > surprise, it again refused to boot. Paul helped us eliminate several
> > possibilities at the Pi Jam in Exeter on Saturday; here's the latest 
> > update.
> >
> > First to recap (well, it's a recap for Paul), at the Pi Jam, with Paul's
> > help, we tried the following (all failed to do anything but show the
> > board's ROM start screen):
>
> There is no ROM startup screen.
>
> > * Different power adapter
> > * Different card, same board
> > * Different board (Paul's, also a Rev B), same card
> >
> > * Mount and check our card on Paul's board booting from Paul's card, 
> > using
> > Paul's USB card reader
> >
> > So we gave up and enjoyed checking out everyone else's geeky stuff, 
> > and it
> > was great, and we went home, and we plugged everything back in the 
> > way it
> > was in the morning, and it booted and ran fine first time.
> >
> > So, I conclude, that the explanation is one of the following:
> >
> > 1. Our board likes using analog composite video out, which is what we 
> > have
> > here, a bit more (but not enough to be deterministic even here) than
> > digital HDMI-to-DVI-D which is what we had in Exeter; or
>
> If using HDMI, then the target device must be enabled and turned on 
> *before* you power up the Pi. The Pi detects the presence of a working 
> HDMI capable device in milliseconds after power up and if it doesn't 
> detect one, it will switch to compost video output.
>
> The initial splash screen is the rainbow square and that's generated 
> by the bootloader read off the SD card by the GPU.
>
> bootcode.bin is read first and runs inside the GPU's L2 cache. This 
> then loads start.elf which parses config.txt and at that point (AIUI) 
> the GPU video is initialised and the rainbow screen is displayed. 
> start.elf then loads kernel.img and cmdline.txt and takes the ARM out 
> of reset and Linux boots.
>
> So this means the Pi read the first 2 files off the SD card which is 
> GPU code and part of the bootloader.
>
> If you see nothing after than then there are a number of potential 
> issues. The first is power - easy to solve, change the PSU. The next 
> is a potentially duff SD card. I've seen this. Not all cards are 
> created the same and the Pi is somewhat fussy.
I was wondering about the card myself.  A friend recently told me that 
some cards, he quoted examples purchased from eBay, are not all they 
should be and there is a utility available for testing a card and making 
sure it is what you were told when you bought it.  I /think/ the utility 
is Windows only, at least that was the one he mentioned to me.  Might be 
worth checking unless the source the card was purchased from was a known 
quantity, ie a local shop.

Julian

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