Write to 0x00 erases memory?

Swys · Joined: 24 Feb 2010 Posts: 22

Hi all,

I am almost done writing a bootloader, save for this problem I'm having...

I wrote a small program to flash an LED which I then load into the PIC with my bootloader. Everything goes fine, until it tries to write to the first two locations in memory (the GOTO instruction at 0x00 and the Reset address). When I attempt this, everything I've just written gets wiped out.

My bootloader resides at the end of the program memory. When it starts, it backups the data at two memory addressess mentioned (0x00 and 0x02) and erases all the data (except for the bootloader, of course). Then, it writes the firmware received from the UART and afterwards attempts to restore the data at 0x00 and 0x02, so that the PIC will automatically jump to the bootloader upon reset. After this, the bootloader jumps to the user program.

When I comment out the two lines to write to 0x00 and 0x02, the loaded firmware is run correctly but, of course, the PIC doesn't know where to go to after a reset.

I am using the PIC24HJ128GP502 for development with version 4.107 of the PCD compiler.

Here is the test program I wrote as well, if it will be of any help. The #build(reset = 0x200) is so that I know exactly where to jump to from the bootloader:

main.c

Gary Smithson · Joined: 13 Feb 2004 Posts: 22

Remember that write_program_memory () automatically erases blocks when the first address of that block is written to. This is described in the compiler help file. Address 0x0000 would be the beginning of a block so when you re-write the reset vector, the leading chunk of your newly bootloaded program is getting erased.

Since you are manually erasing memory before the bootload, you should probably be using write_program_eeprom (), which does not automatically erase blocks.

Hope that helps,
Gary

Swys · Joined: 24 Feb 2010 Posts: 22

Thanks for the answer, Gary.

Unfortunately, this does not work. When I try calling write_program_eeprom(), CCS only returns with "Undefined identifier - write_program_eeprom". I couldn't find the topic on this function in the reference manual, although there are links to it in the manual (that don't work).

Is this function maybe called something else that is not documented?

Gary Smithson · Joined: 13 Feb 2004 Posts: 22

Welcome to the downside of using CCS compilers.

This is likely a CCS "bug" that needs reporting. The function should be available at compile time, it should work as advertised, it should be described in more detail in the manual, and the manual search features should lead the user to its documentation. Please report the problem to CCS. They do not act on forum posts as bug reports.

If you can convince them to respond quickly, that will be the fastest way to solve your problem. Other solutions such as writing the function yourself will require significant time.

Gary

miketwo · Joined: 04 Aug 2010 Posts: 24

Resurrecting this topic after 4 years, cause I'm basically trying to do the same thing. (Bootloader at end of program memory, "goto bootloader" at beginning of memory.

Swys, did you end up solving your problem?

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

miketwo · Joined: 04 Aug 2010 Posts: 24

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

Technically, PIC 18 has a erase block size of 64 bytes and program size of 16 bytes. To rewrite a flash memory block, it has to be erased before unless it was left unprogrammed since last erase action. You can't rewrite individual words of program flash.