The LPC55xx / LPC55Sxx is an Cortex-M33 based microcontroller for embedded applications including a Cortex-M33 co-processor.
In case some bad code has been flashed into the device (wrong PLL init that bricks the device, ...) that makes it unresponsive to debug commands, there is no built-in mechanism that allows J-Link to regain control over the device, however the device is not lost yet.
LPC55xx / LPC55Sxx series devices provide a specific pin to enter ISP mode on boot which effectively inhibits starting the user application and therefore the bad code. In order to recover an LPC55xx / LPC55Sxx series device that is running bad code, the following needs to be done:
- Short PIO0_5 with GND
- Power-cycle the device (make sure that LOW is sampled on PIO0_5)
- Release PIO0_5
- Start J-Link Commander, J-Flash or any other utility that supports J-Link and reflash the device
NOTE: On the LPC55S69-EVK there is a separate "ISP" button which can be used for this purpose.