I am invoking iap_entry to force it into ISP mode using UART 0, regardless of the ISP0/1/2 pin state. I use ISP_ReinvokeISP provided in fsl_iap.h with these arguments:
uint32_t status = 0;
IAP_Reinvoke(1, &status); // Argument 1 as 1 forces booting into ISP UART mode according to documentation
However, this always fails with status = ERR_ISP_REINVOKE_ISP_CONFIG
This is on a LPC51U68 using the LPCXpresso demo board. I do have UART clocks enabled at this time.
Does this processor support iap_entry to boot into ISP mode? Or are there other conditions I need in place before calling ISP_ReinvokeISP?