Yes, I used your technique of creating the variable 'INIT' inside an ASM block that was at the end of my PBP code. That worked fine.

If you remember, the goal was to make a "hardware write protected bootloader" - one that could (hopefully) be loaded in the field without a PIC programmer. I put MCLoader in all chips. You also have to understand that a LOT of my stuff goes to the military, and they have some strange requirements, hence the demand for this "write protect" feature.

I wrote a program (in PBP) that "field-patches" MCLoader. I got to the upper half of the 18F8722's program space by modifying PBPP18.LIB with a new system variable ('UPMEM') that loads into TBLPTRU. By setting this to "1" I can use READCODE, ERASECODE and WRITECODE in upper half of FLASH. If UPMEM is "0" these commands work in the lower half.

My PBP program changes the MCStudio jump vector at 0x00 from 0x1fd04 to 0x1fcd0, and adds a statement at 0x1fcd0 to jump to 0x1fd04 (the start of MCLoader).

That takes care of the first-time load using the bootloader - we load ALL our code, including the first time, using MCLoader.

Next, my actual PBP application contained an ASM block at the end with an ORG at 0x1fcd0. It checked whether a pin was high or low, and decided either to jump to 0x1fd04 or INIT. The bootloader was invoked when the pin was low (it is pulled up) or else it jumps to the program start, bypassing the autoloader. This gave the "write protect" feature I was looking for.

So far, so good - except for one thing... The FLASH is automatically erased before programming. Since my new jump vector at 0x00 pointed to a normally unused address in the codespace, if programming was interrupted before MCLoader could get the application all the way "in", the chip could no longer be programmed in the field - it is back to the factory time. This can be a real pain if the board is deeply embedded in some submarine, tank or airplane.

I really wanted to locate the "new addition" to the bootloader (the test for pin high or low) to an address ABOVE MCLoader. There are a few more than 64 bytes above the top of that program in an '8720 or '8722. This is handy, since the block size of the ERASE in both chips is 64 bytes.

So, I re-wrote my "bootloader patcher" to change the 0x00 vector to 0x1ffc0 (which is a few bytes above the top of MCLoader). I also wrote my "test for pin state" (and a few other things) in assembly and put its start address at
0x1fc0. I found, by inspecting a lot of code, that PBP was always setting the INIT address to 0x59a, so I test for my pin state and jump to either 0x59a or 0x1fd04, the start of MCLoader.

So far, it has been working perfectly, and the good thing is that I can pull the power plug halfway through programming, and later restart the programming cycle. My only concern is that I have my INIT vector hard-coded at 0x59a, and I'm worried that it won't always work.

WHEW!