Bootloader restart in loop when no program is loaded : How ?

[spilz]

Hi everybody !

I have a problem with my electronic system and I need your help

Description of the Electronic part :

one PIC18F2550
one quartz 20MHz
battery 3.7V always connected
USB is used to charge the battery and connect to the pic to load program via bootloader
pin_a5 detect if USB is connected
pin_a1 is the only switch I have
NO MCLR, no external system to restart the PIC

In normal used (bootloader and program load):

- usb deconnected : program runs, even if the PIC restart, the bootloader don't try to load a new program.
- usb connected, switch off : program runs, battery charges
- usb connected, switch on : program detect it, restart, in bootloader start to charge new program

PROBLEM :

How to do the first time I need to load the program ?

I need that when there is no program loaded, the PIC restart and check USB and switch again and again.

Thanks for your help,
sorry for my english

[Ttelmah]

When you program the bootloader, it does a jump to a dummy one line 'application'. Make this application just be the line 'restart_cpu'. If no other program has been loaded, code will keep on restarting and trying again.

Best Wishes

[spilz]

Thanks for your interest.

It the idea, but how to code this 'restart_cpu' as default value (before the first program is loaded)?

Something like #rom int8 ... ?

[Ttelmah]

You do understand that to use a bootloader, you _have_ to program it into the chip with a conventional programmer before you can start?.
When you program this you include the restart_cpu instruction.
If you don't want to program the chips, or don't have the tools to do this, the chip suppliers will pre-program them for you (usually for a small setup fee).

Best Wishes

[spilz]

Yes I know what is a bootloader,
my problem is that i can not disconnect the battery, so I can not restart the pic when I want.

So the problem is how to load the bootloader AND the "reset_cpu" with the programmer at the same time, and after, be able to load the new program to replace the "reset_cpu".

So I think we have to write the "reset_cpu" where the new program will be write...
not sure I'm understandable

[PCM programmer]

Read this discussion of different ways to tell a bootloader to go into
"bootload" mode:
http://www.ccsinfo.com/forum/viewtopic.php?t=48925

[Ttelmah]

[spilz]

Hi Ttelmah,

It's exactly what I was looking for THANK YOU

My other question is :

If there is a probleme when the program is downloaded (for exemple the usb cable is deconnected during download or error during downloading) How to rewrite as default this reset_cpu ?

I'm working on a system that will be used by "normal people" who just want to be able to update the system, and I want to minimize the risk of "bricking" the system.

[Ttelmah]

Obvious approach, is to load the page of ROM at this point (one byte after loader_end) into RAM when you start programming the chip, and if the data fails at any point, write this page back.

Best Wishes

[spilz]

yes, it's the idea, but I don't know how do to that,

something like :

[Ttelmah]

That's why I said read the block.
Simplest way. Put's the correct bytes in the correct location. However It's actually just a simple 'reset' instruction (data sheet) - 0x00FF.

Best Wishes

[spilz]

what do you mean by "read the block", i'm not sure to understand