Secondary bootloader

[Manwan]

For LPC845, it mentioned secondary bootloader in the application note, but not for LPC824, so what is the difference of the primary and secondary bootloader, when should the secondary bootloader be used?

[frank_m · Accepted solution]

An internal bootloader is usually implemented in ROM, and started when certain startup conditions (levels in ISP/BOOT pins) are met. This BL application is fixed, which has it pros and cons.

A secondary bootloader is basically a normal application located in Flash.

What makes it a "bootloader" is your functionality - loading updated firmware, flash it, erase old version, and execute the firmware.

Such a secondary BL needs to avoid erasing itself (sometimes less trivial as it seems), and the applications need to linked for this BL specifically - i.e. application linkage requires modification.

[Manwan]

Hi Frank, thanks for your reply and kind reminder, and what confuses me is they didn't call these(functionality - loading updated firmware, flash it, erase old version, and execute the firmware) as secondary bootloader on the other chips, like LPC824, to me it seems they are the same kind of "bootloader" we made on other chips, programmed in the beginning of flash to update firmware.

I guess they are the same thing, it is just on LPC845, I2C and SPI is supported as well, but on LPC824, only UART0.

[frank_m]

> I guess they are the same thing, it is just on LPC845, I2C and SPI is supported as well, but on LPC824, only UART0.

That depends on your application. Often, you do not get along with the interfaces and protocols the internal/ROM bootloader supports, and need to use a "secondary" one.

Having to deal with ECUs in my dayjob, hardly any MCU we use supports CAN via bootloader. Thus we have to maintain our own bootloaders.

[Manwan]

Really appreciate your reply, Frank, got it.