Lpc2000

John,

I normally ask that one includes in the requirement only what one
wants, not how one wants it done.  If you do this, then you are not
likely to introduce undesirable side effects.

You want alternate boot loader intercepts like I said I wanted in the
free boot loader proposal.  I can see that the way you want it done
adds another method to how the LPC part can be locked out by software.

As it stands, the LPC can be locked out by software if the boot loader
is corrupted in way what it disables JTAG and then spin loops.

Consider your enhanced bootloader in which the the user enables CRP
*and* boot loader intercept, the intercept call does not return or
unconditionally returns "bypass as if P0.14 is false".

The part is now locked out by software and is as good as a OTP with
the application code as loaded and without boot loader functionality.

I would be surprised if Philips would implement your method and
introduce yet another software method by which users could lockout
their parts.

There are other issues but I have to explain these the context of what
the current boot loader on-chip does on startup, and why it is not a
good idea to branch to user code then back in the context of CRP.

Regards,

Jaya

--- In lpc2000@yahoogroups.com, "John Heenan" <l10@...> wrote:
>
> Below is a draft of a possible sensible formal request we could make 
> to Philips with regard to bootloader enhancement. It is simple and 
> practical. 
> 
> If Philips agrees we can use interrupts by copying interrupt 
> instructions and constant addresses to the start of RAM and setting 
> MEMMAP to RAM mode. We can still use IAP features of the bootloader. 
> 
> There is no sense in replacing the bootloader if you accept it does 
> its job as is: why chuck IAP when it works great and can be used to 
> advantage in an enhancement, such as with USB enhanced bootloading?
> 
> John Heenan
> 
> 
> Dear Philips
> 
> This is a formal request with regard to the bootloader of the LPC2xxx 
> series of microcontrollers.
> 
> We are requesting a small enhancement to the bootloader whose end 
> functionality is to 
> - give us an option to bypass the pin 0.14 test by the bootloader 
> when there has been an external reset
> - perform our own bootload tasks taking advantage of IAP if we want to
> - rejoin the bootloader informing the bootloader what we now want it 
> to do or what we have done
> 
> For existing LPC2xxx parts with flash based bootloaders we are 
> requesting you make an upgrade to the bootloader available to us.
> 
> For the bootloader to decide to bypass four items of information are 
> necessary
> 1. Whether to bypass
> 2. Where to bypass to (in supervisor mode expecting ARM instructions)
> 3. Where we need to return to if we want to return ('BX LR' is a good 
> option)
> 4. What should be specified in a register on return
> 
> On return perhaps R0 could have a value to indicate one of the above
> 
> - conduct a normal pin 0.14 test
> - bypass pin 0.14 test as if test is true 
> - bypass pin 0.14 test as if test was false
> - we have used IAP functions to conduct our own bootloading: please 
> restart the bootloader as if there was an external reset
> 
> Currently address 0x1FC is used to store the CRP value. If this value 
> is 0x8765 4321 (or 0x4321 8765) then Code Read Protection (CRP )is 
> enabled.
> 
> If CRP is not enabled then we request that if the CRP value is 0x4321-
> --- or 0x----4321 where ---- represents four hexadecimal digits then 
> these hexadecimal digits be used to decide a multiple of 4kB to jump 
> to. For example if the CRP value is 0x4321 001E or 0x001E 4321 then 
> this is interpreted to call address 0x1E (decimal 30) times 4kB = 
> 0x0007 B000. This is the start of sector 25 on the LPC2148 and is the 
> start of the last 8kB of flash on the LPC2148.
> 
> Given that no flash sector can be less than 4kB for erase purposes 
> (they are either 4kB or 32kB) then there is no advantage in 
> specifying a finer resolution than 4kB as a multiple for call purposes
> 
> This request has the support of the following members of the LPC2000 
> newsgroup on http://groups.yahoo.com/group/lpc2000/
> 
> John Heenan
> Add your name if you support such a request!

Count me out!