The intermediate programming feature allows the programming of external flash memory located on the board along with the microcontroller. Programmer is connected to the microcontroller by interface e.g. JTAG/SWD and flash memory is connected to microcontroller e.g. by Quad SPI interface. As a result, only one connection is used for programming the internal memory of the microcontroller and external flash memory. This feature makes the manufacturing process easier.
XStreamPro Flash programming NXP + Micron (MK8 + MT25QL128)
https://youtu.be/LVv5thF5h7YElprotronic Inc. XStreamPro programming video. NXP MK8 + Micron MT25QL128 external flash. Tutorial presents programming procedure of external flash memory connected to MCU pins by single-target FlashPro-ARM programmer.