Fault Tolerant bootloader and interrupt vector

[moutinho]

Hi,

I have implemented a bootloader process using a GPRS modem. I am now working on issues related to fault tolerance such as a power failure during the update process.
I intend to change the interrupt vector during the update process and then swap to main() after the process is finished. If any failure happens during the update process, the process is restarted by jumping to bootloader area throught the reset vector.
I have used the write_program_memory() but it seems to erase a large memory area and I only need to replace the beginning four program fash code (GOTO XXXX).
Questions:
1) Is there a way to write only the desired four bytes program into 0x00000 flash location without erasing a large block (4 bytes used + remaining 63 bytes)?
2) Can I change the interrupt vector during program execution ?
3) Do I need to set another configuration such as fuses, etc ?

Thanks,
Andre

[Mark]

Read the datasheet on the PIC that you are using. It will tell you the block size that must be erased. So to answer your question, no you can't just erase 4 bytes.

Why change the interrupt vector at all? Just do a test to see if you are in Bootloader mode. If so, the go HERE Else go THERE.

Can't change the fuses with bootloader.

[moutinho]

Hi,

I can�t do if so, then go HERE else go THERE, because once the memory update process is started, the main code is also updated. If any failure occurs during the main code write, the next reset process will not be able to restart the update process. The memory will be corrupted.

Thanks,
Andre

>

[Mark]

Well I can do it so you should be able to as well. You probably don't understand what I mean so I will explain a bit more.

First off, the bootloader never gets changed so it always works (not really, I have a separate way of changing it if I want to but for this purpose it won't change). Now since the bootloader never changes, I should always be able to download new code in the event of a failure if I can enter bootloader mode. Well that is accomplished using a flag that is set and stored in the data eeprom of the device. There are a couple of ways mine can enter bootloader mode but basically they all store a value in the eeprom. On startup, this location is read and if the magic value is there, then I continue with the bootloader if not then I goto main. Notice that I said continue with the bootloader. That means that I always enter bootloader mode first and then decide if I should be in it or not.

[moutinho]

>Notice that I said continue with the bootloader. That means that I >always enter bootloader mode first and then decide if I should be in it or >not

Hi,
This is a good idea. I have thought to do it but I didn�t what to have my main() function application as the bootloader (). There exist a way to tell the compiler to start the execution at another function instead of main() ?

Thanks,
Andre

[Mark]

You would have 2 mains. Your bootloader main would goto the main of the application.

I used another compiler for my apps that have a bootloader you should be able to accomplish the same thing with this compiler the syntax is just a bit different.

[moutinho]

I will check this.
Thanks
Adnre

[bfemmel]

moutinho,

To get the boot loader to survive a power outage or problem during download, the boot loader needs to behave like a separate program but doesn't need to be one.

In the main program, a command to download new code will cause the program to branch to the boot loader which is loaded at the top of the memory area. The first thing the boot loader does when we jump to that routine is to turn off all the interupts and reset the hardware. Then we replace the reset vector to jump to the load routine on startup. That way if the load is interrupted the program will start back at the loader instead of running garbage code. When the new code is installed, the last thing it will do is to replace the reset vector to the start of the new program.