App note from NXP on updating LPC86x firmware safely on-the-fly with their I2C secondary bootloader. Link here (PDF)
The secondary bootloader (SBL) described and implemented in this application note provides a solution for the host processor to program the slave processor. It utilizes the IAP functionalities of boot ROM and allows programming the LPC86x flash through I2C slave interface, which is the common interface used between the host processor (referred to as AP in a sensor hub application) and the sensor hub.