Re: [PIC] Community ed class by olin

Gerhard Fiedler wrote: > If you don't write-protect the configuration registers, you could > write-protect the boot block in the bootloader after writing the > application code. Which would make it a two-step process for a "bad" > application to take the bootloader out: it would have to change the > write protection for the boot block in the configuration register, then > take over the boot vector by writing to it. Maybe that's good enough... > at least good enough against accidentally taking over? > > Probably the only safe way is to put the bootloader in the boot block > and to write protect both the boot block and the configuration > registers. But this requires that the application is linked to start at > an address above the bootloader. (If there wasn't the issue with code > pages, this would look different :) I think you are making this way to complicated. In practise I've never seen an application accidentally write over a bootloader on a PIC. It can theoretically happen, and probably has, but it is very rare. How many TBLWRT instructions does your app have? Unless it's a bootloader, probably none. A few apps may modify an occasional table based on calibration data or whatever, but this is a small minority of apps. A buggy app could start executing data as instructions, which could in theory write to program memory, but this requires a very unusual alignment of quite a few stars. The worst danger is from a buggy app that contains deliberate code for writing to program memory. This is not something a beginner would be doing. ****************************************************************** Embed Inc, Littleton Massachusetts, (978) 742-9014. #1 PIC consultant in 2004 program year. http://www.embedinc.com/products