USB Bootloader for LPC1768-H Blue Board

The JTAG debugger has been working quite well. But it needs a parallel port which most laptops including my own lack. LPC17xx conveniently supports USB device interface which can be used for bootloading. USB is ubiquitous and using it will obviate the need for any extra programming hardware.

If you don't know what a bootloader is, then you should read this tutorial in sparkfun. The bootloader presented there is targeted to LPC2148 which is based on the ARM7TDMI core which differs quite a bit from the Cortex M3 on which the LPC1768 is based on. So, you need to read only enough to understand what a USB bootloader is.

NXP has provided a USB secondary bootloader as a sample program along with their app note on how to use mass storage device class. Here is the app note along with the code. You'll need Keil uVision 4 to compile the code. A free version which compiles upto 32 kB is available. This is sufficient since the bootloader itself occupies only 8 kB of flash. If you don't intend on modifying the code, look at the attachment below. A link to the HEX file which can be burnt is given.

The bootloader code will upon reset, check the status of a certain pin and decide whether to enter the bootloader or execute the user code. The default pin checked by the NXP USB bootloader is not mapped to a switch on the LPC1768-H Blue Board. A quick look at the schematic of the blueboard reveals that the only usable switch is connected to P2.10. This unfortunately is also the pin tested by the default UART bootloader present in all NXP LPC17xx chips. So, holding the switch and pressing reset till cause entry into the UART bootloader. Because, that is the only pin to which a switch is connected, we are forced to use that to signal the entry into a bootloader. A slight modification to the code given by NXP is thus necessary.

The idea is to capture the status of P2.10 not immediately after reset but after a gap a second or two. The modified bootloader will upon reset, turn on the test LED and wait for about 3 seconds. If during that period, the switch is pressed (P2.10 goes LOW), the bootloader is launched. If however, no key press is detected by the end of 3 secs( the test LED glows during this time), user code, if present is launched. It is important to see that, P2.10 should not be held LOW while resetting the CPU. Doing so will cause NXP's UART bootloader to launch on reset since it is that program which samples P2.10 first. The switch should be pressed only after the test LED glows indicating the secondary USB bootloader is sampling P2.10 and not NXP's UART bootloader.Subsequently, the bootloader will function as described in the app note. The only change is the entry method.

Here is the modified code.
And the HEX File.

Now, one small change is necessary in the linker file of the user programs ( that will be loaded by the bootloader onto the chip). The bootloader itself resides at 0x00000000 and uses 8 KB of space. So the user program should begin at 0x00002000. This should be explicitly stated in the linker file.

The code base that can be used to jump start the project with an editor like eclipse is here. Note that I've modified the flash start address in the linker file to 8 KB so that this code base can be used to generate bin files needed for bootloading.

You should modify the start flash address ( to 0x00002000 from 0x00000000 ) in the linker file of the user program if you are using some other code base.

EDIT :

I've added all these files in google code.