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'[pic]: bootloader software'
2003\01\20@221424 by rad0

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what exactly is going on when you use a bootloader?
and is this a difficult assembly language program?

when you use a boot loader program, there is a programmed delay upon
power up(correct?), then the program gets loaded into hi memory,
or somewhere - where the pic uses it upon re-power up, after the delay


so how does this work?


I'd like to right a simple bootloader program, in assembly.

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2003\01\20@230932 by Brent Brown

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On 20 Jan 2003 at 21:12, rad0 wrote:

> what exactly is going on when you use a bootloader?
> and is this a difficult assembly language program?
>
> when you use a boot loader program, there is a programmed delay upon
> power up(correct?), then the program gets loaded into hi memory, or
> somewhere - where the pic uses it upon re-power up, after the delay
>
>
> so how does this work?
>
>
> I'd like to right a simple bootloader program, in assembly.
>

Yeah, kind of works like that. I like this one at:
http://www.microchipc.com/

The assembly source code is provided so you can see how it works.

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2003\01\21@031804 by Wouter van Ooijen

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> what exactly is going on when you use a bootloader?
> and is this a difficult assembly language program?

Depends on what you find difficult.

> when you use a boot loader program, there is a programmed delay upon
> power up(correct?), then the program gets loaded into hi memory,
> or somewhere - where the pic uses it upon re-power up, after the delay

There must be some trigger to start the application, for instance
- a time delay without communication, as you mention
- a 'go' command over the comms link
- an inactive comms link (no PC connected)
- a dedicated input pin

> I'd like to right a simple bootloader program, in assembly.

http://www.voti.nl/wloader page contains links to some other
boorloaders.

Wouter van Ooijen

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2003\01\21@083033 by Olin Lathrop

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> what exactly is going on when you use a bootloader?

A "bootloader", despite the term, is usually meant here as a means to
upload new code onto a PIC, not to load the code every time the PIC is
started.

> and is this a difficult assembly language program?

Like most programs, doing a quick and dirty one isn't that hard.  A good
one isn't hard either, but there are a few tricky issues to consider.  I
sortof remember my last PIC bootloader was 300+ instructions.

> when you use a boot loader program, there is a programmed delay upon
> power up(correct?),

Depends on what you want.  I sent a byte to the host letting it know new
firmware could be uploaded, then waited 100mS for the host to respond.  If
it didn't, then the bootloader ran the stored application if it looked
right.

> then the program gets loaded into hi memory,
> or somewhere - where the pic uses it upon re-power up, after the delay

Pretty much.

> so how does this work?

See above.

> I'd like to right a simple bootloader program, in assembly.

So do it.

Here are a few issues.  I'll let you think about them instead of answering
them:

1  -  What if power goes down or communication got corrupted during an
upload.  This would trash the application program.

2  -  Should the bootloader allow itself to be overwritten?  If not, how
does it know its own addresses?

3  -  What exactly gets written to the reset vector?

4  -  Do you want to be able to upload a new bootloader?

5  -  What pins will the bootloader claim?  Can these be reused by the
application?


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2003\01\21@143157 by Peter L. Peres

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On Mon, 20 Jan 2003, rad0 wrote:

*>what exactly is going on when you use a bootloader?

The bootloader is a sort of resident monitor that communicates with a host
(a pc) to allow it to program parts of the micro with new code. It also
usually has a number of other functions.

*>and is this a difficult assembly language program?

It contains at least a complete terminal program, a command interpreter of
some sort, and a complete in-chip programmer.

*>when you use a boot loader program, there is a programmed delay upon
*>power up(correct?), then the program gets loaded into hi memory,
*>or somewhere - where the pic uses it upon re-power up, after the delay

The delay serves to give the host time to send commands. If the loader
sees no commands it starts running the code in the chip. Else if executes
commands from the host. This allows development/production use without
using any switches.

Peter

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