hello every body!!!
I want to design an token .
I need that it cab be programed through the USB buy I don't want to use any switch on it for loading sam_ba.
please help me.

a) Call into the ROM, figure out the state and address required and jump in.

b) Invalidate the boot vectors in you NOR/NAND boot strap device, and reset.

[quote="CptTitanic"]a) Call into the ROM, figure out the state and address required and jump in.

b) Invalidate the boot vectors in you NOR/NAND boot strap device, and reset.[/quote]


**********thanks a lot for your solution*********
Can you explain it in detail for me ;
I don't understand your solution completely ,I'm a starter.

Then I think you need to start out by becoming more familiar with the ARM7 architecture, and writing simple applications to reset and programming internal/external memory, and perhaps move code into RAM and execute it from there.

For example do you really need to replace the entire application within your "token", or is it simply necessary to write some specific function or key information in it to make it unique.

The most viable solution really would depend on exactly what the problem is, and without a more clear idea of the what's and why's, I'm not even sure your current path is even appropriate. If this is a commercial project, you might want to consult with some more experience engineers/programmers.

Do you have the ability to look at the current boot code?

Have you considered putting magic constants in RAM, and using these to alter the behaviour of your boot code at startup, instead of reading a button state?

hello,my good friend.
before everything,thanks for your attention to my question.

In fact, I want to design a token and I must consider this parameters:
1.the chip is at91sam7s256 and I can't choose another one.
2.the code is important so after programming the code on chip, I must set security bit of chip;so I must erase it (with active high erase pin) to reprogramming it.(so I can't use a boot loader that is written with me because before reprogramming it will be erase) .
3.the token is packed after design ,so I don't have any access to hardware via ports or pins or other ways , to programming or reprogramming it.
4.it has a usb port only , that can connect to computer such as a cooldisk .so I must program the code on it via usb (I think it is possible only by loading sam-ba from rom to nandflash with a0,a1,a2,tst but before it must be erased ).
5.I can use an external programmer to load sam-ba if it is possible.


these are important parameters that I remembered.
thanks.