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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.
Check config.txt and cmdline.txt - just in-case they're corrupt in some way.
Or something else is wrong.... But if you have a voltmeter then check between T1 and T2 - ought to be >= 4.8v.
Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/listfaq