The SD bootloader is used to facilitate firmware updates : You only need to flash it once, and it makes the first firmware flashing and subsequent firmware updates much more simple.

Basically at boot/reset, it looks for the firmware.bin file on the SD card, and if found, flashes it to the board's FLASH memory ( then renames the file to firmware.cur, so check for that to see if it worked ).

So once the bootloader is installed, updating the firmware is as simple as copying it to the SD card and reset.

The bootloader was written by Triffid_Hunter and can be found here on github.

LPCXpresso1769 or SmoothieBoard

To flash the bootloader you need a Serial-USB ( can be a FTDI cable, an arduino, CP2102, etc ) cable connected to the UART0 pins of the LPC1769 ( 6-pin connector noted as "Serial" on a smoothieboard ), and the "reset" and "bootloader" (ISP) buttons connected.

If you have a Smoothieboard, all of this is already there, just connect the Serial-USB/FTDI cable. ( well actually if you have a SmoothieBoard it comes the with the bootloader pre-flashed, just move ahead to the actual firmware flashing. Except for the beta board where you might want to flash anyway to get SDHC support ).
If you have a LPCXpresso1769, you want to look at Smoothie On A Breadboard for how to wire the serial cable and the buttons.

Entering bootloader mode

In order to flash the SD bootloader to the chip, you must first enter the Serial Bootloader mode. This mode allows you to write new code to the FLASH memory via UART0.
To enter this mode do the following : 

• Press the RESET button
• Press the BOOTLOADER (ISP) button
• Release the RESET button
• Release the BOOTLOADER (ISP) button

Flashing the SD bootloader

First install the lpc21isp program if you are using linux, or the FlashMagic tool if you are using Windows. For 64-bit OS X, lpc21isp is checked into Smoothie's git repository under the build/osx64/lpc21isp directory.

For FlashMagic you have to set the proper LPC device (or better select menu ISP>Read Device Signature.. ) and select COM port of your cable. Use 38400 Baud, Interface None (ISP) and Oscillator 12 MHz, check "erase blocks used by hex file". After selecting your HEX file and pressing the "Start" button FlashMagic will program it.

You can either compile the bootloader from source, or simply download the .hex file here. Simply clicking the link may display it as a text file. You may need to do a "save as" to download the file.

Flashing pretty simple for windows, simply feed it the .hex file.

For linux you want to do the following : 

lpc21isp -wipe DFU-Bootloader.hex /dev/ttyACM0 230400 12000

Change /dev/ttyACM0 to whatever matches your Serial-USB cable.

Now flashing occurs, and that's it!

Mbed

Because the mBed has its own USB flashing thing, you don't want to use the SD bootloader with it.

Instead simply replace the file mbed/src/vendor/NXP/cmsis/LPC1768/GCC_ARM/LPC1768.ld , with this

Localstorage does not work out of the box with the mbed. But you can place your config into src/config.default. Your configuration will then be included in the firmware.bin

If want to use pins P0_9, P0_8, P0_7, P0_6, you need to comment SDcard support in src/main.cpp

//SDCard sd(P0_9, P0_8, P0_7, P0_6);      // this selects SPI1 as the sdcard as it is on Smoothieboard

To create the Smoothie firmware run the following command from the root Smoothie directory.

./BuildShell && make clean all

Once you have compiled Smoothie simply copy the generated LPC1768/main.bin file to the mBed's drive.

A working fork is available here

//Old:
You can find a more detailed guide at running smoothie on the mbed here.

Direct Serial Bootloader flashing

Instead of using mBed's own USB flashing util, we can use the lpc21isp program to flash Smoothieware directly.
This means we will not be getting SD card support, as we'll be flashing over the SD bootloader.

The approach is similar to what's explained in the Mbed section.

A working fork for this based upon the Mbed usb flashing, can be found here