Doubt regarding Boot Loader

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Posted by Indranil

on Apr 12 2012 02:22 AM

Hi, I am using my custom-built LM3S9B92 board for my project. I have programmed the serial bootloader(boot_serial.bin) available in C:/StellarisWare/boards/dk-lm3s9b96 folder after compiling it.... at program offset 0x0 using LM Flash programmer ( interface used is JTAG) . Moreover I am using one GPIO pin to pass control to the bootloader or application program after reset. Then I tried to program some example programs into the flash using LM flash programmer such as usb_host_msc (interface used is UART now). The programming happened succesfully using boot loader. But my doubt is the APP_BASE as referred in bl_config.h file is 0x1800 which means while programming through LM flash programmer do I have to specify the program address offset to 0x1800. But the program offset what I have entered is 0x00...so without doing this also the flash has been succesfully programmed using serial bootloader which shouldn't happened as per my understanding. So my question is if my boot loader is already sitting in flash at position 0x00, after programming through UART where will my application program will sit because I am giving same offset address in both cases ? Will it be going to position 0x1800 automatically(will be taken care by bootloader)? Moreover in usb_host_msc_ccs.cmd file ..or whatever sample programs I am trying out, everywhere the application base APP_BASE (flash starting address ) is defined as 0x00000000 which is contradicting application starting point mentioned in bl_config.h file. Am I doing it correctly or am I missing some point ? Please help me. With regards, Indranil

Indranil

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Posted by Stellaris John

on Apr 12 2012 14:40 PM

Intellectual2130 points

Indranil,

If you set the program address for your application to 0x0 in LMFLASH when you use the serial bootloader, then the bootloader will overwrite itself with the program. You should specify the offset in LMFLASH at 0x1800.

If you want to have CCS not overwrite the bootloader when you use CCS to program the application into the flash, you will need to change the .cmd file to have an APP_BASE of 0x00001800 as well. The .cmd files in the boot_demo examples in Stellarisware should show you how an application can be run from the bootloader.

Remember to reduce the length of the flash in the .cmd file when you increase the program's starting address so you don't try to write past the flash area.

Posted by Indranil

on Apr 12 2012 23:29 PM

Prodigy130 points

Hi John,

Thanks for your reply.

Actually I have misunderstood this whole bootloader concept. But now after playing with bootloader and going through the TI documents and example programs, now I understood how actually bootloader is working. Previously I thought my serial_boot program is actually programming my flash everytime ...so I get confused. But now I came to know that its actually the ROM bootloader that is taking control when I use one of my GPIO pin to decide whether I want to go to ROM bootloader or application part.

Moreover now I get the idea about the APP_BASE. When I am using ROM bootloader I shouldn't change the .cmd file to other address other than 0x00. It should need to be change only if I use the example serial_boot program ..am I right ?

With regards,

Indranil

Indranil

Posted by Stellaris John

on Apr 13 2012 09:49 AM

Intellectual2130 points

Indranil,

Yes you are right. If you are using the ROM bootloader, your apps should start at 0x00. This is why the examples in Stellarisware except for boot_demo start from 0x00.