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Re: [LUG] Pi mystery


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.


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