On 21/03/14 10:10, Jason White wrote:
How much extra would it cost manufacturers to design devices so that there's a backup boot loader in ROM which can't be overwritten?
For many devices these days, "ROM" _is_ flash, perhaps with a write protect or security bit set. It isn't just a cost disadvantage to add a real ROM, it also wastes board space, and it means that a code error in the boot loader can't even be fixed with a factory recall. The problem isn't that hard. If a manufacturer really wants us to be able to change the software, they just provide a two stage loader; a simple one in a write protected area, to load in a more generic operating system loader that is user replaceable. This does take a little planning, because the manufacturer has to find a user accessible way to provide a code update, and a way to force the boot loader on initialization, eg by holding down some button combination and holding up your left arm in the air. Many devices work this way already; it isn't a significant increase in development cost. For example, I have a Linux based ereader which allows you to reflash it simply by powering up after inserting an SD card with an appropriately formatted binary. It is relatively foolproof, because the SD card is checked by the boot loader on startup, and there is no need to ever overwrite the original boot loader. The key point here though is that some manufacturers don't particularly want their users to change the software, and go out of their way to make it difficult. This leads to boot loader workarounds which might carry the risk of an unrecoverable state. But I do think that if a smartphone is being sold as a computing device, then we can reasonably expect to be able to run the software of our choice, otherwise it is a dumbphone. If the result of workarounds is a brickedphone, then I think that the seller should take at least some of the responsibility for deliberately making it difficult to change the software. If someone sold me a ceramic bowl, but the packaging was such that I couldn't unwrap the thing without a high risk of breaking it, then I wouldn't be happy. Likewise, I have no desire to buy a computing device for which installing different software carries a significant risk of bricking it. Glenn -- sks-keyservers.net 0x6d656d65