IAP on LPC microcontroller

Question

This code is part of IAP on an LPC:

#define IAP_LOCATION 0x7ffffff1
...
unsigned long command[5];
unsigned long result[3];
...
typedef void (*IAP)(unsigned int [],unsigned int[]);
IAP iap_entry;

iap_entry = (IAP) IAP_LOCATION;

iap_entry(command, result);

Can someone explain how it works, especially:

iap_entry = (IAP) IAP_LOCATION;

iap_entry(command, result)

Answer 1

typedef void (*IAP)(unsigned int [],unsigned int[]);

IAP is the type pointer to function(unsigned int[], unsigned int[]) returning void

iap_entry = (IAP) IAP_LOCATION;

There is some code at address IAP_LOCATION. Treat it as a C function.

iap_entry(command, result);

Call the function

---

Typically, this happens when a piece of hardware contains a ROM with precompiled code. You have to tell the C compiler where this code is in memory, and what argument types it expects.