cmsis_nvic.c

00001 /* mbed Microcontroller Library - cmsis_nvic for LPC11U24
00002  * Copyright (c) 2011 ARM Limited. All rights reserved.
00003  *
00004  * CMSIS-style functionality to support dynamic vectors
00005  */ 
00006 
00007 #include "cmsis_nvic.h"
00008 
00009 /* In the M0, there is no VTOR. In the LPC range such as the LPC11U,
00010  * whilst the vector table may only be something like 48 entries (192 bytes, 0xC0), 
00011  * the SYSMEMREMAP register actually remaps the memory from 0x10000000-0x100001FF 
00012  * to adress 0x0-0x1FF. In this case, RAM can be addressed at both 0x10000000 and 0x0
00013  * 
00014  * If we just copy the vectors to RAM and switch the SYSMEMMAP, any accesses to FLASH
00015  * above the vector table before 0x200 will actually go to RAM. So we need to provide 
00016  * a solution where the compiler gets the right results based on the memory map
00017  *
00018  * Option 1 - We allocate and copy 0x200 of RAM rather than just the table
00019  *  - const data and instructions before 0x200 will be copied to and fetched/exec from RAM
00020  *  - RAM overhead: 0x200 - 0xC0 = 320 bytes, FLASH overhead: 0
00021  * 
00022  * Option 2 - We pad the flash to 0x200 to ensure the compiler doesn't allocate anything there  
00023  *  - No flash accesses will go to ram, as there will be nothing there
00024  *  - RAM only needs to be allocated for the vectors, as all other ram addresses are normal
00025  *  - RAM overhead: 0, FLASH overhead: 320 bytes
00026  *
00027  * Option 2 is the one to go for, as RAM is the most valuable resource
00028  */
00029 
00030 #define NVIC_NUM_VECTORS (16 + 32)            // CORE + MCU Peripherals
00031 #define NVIC_RAM_VECTOR_ADDRESS (0x10000000)  // Vectors positioned at start of RAM
00032 
00033 void NVIC_SetVector(IRQn_Type  IRQn, uint32_t vector) {
00034     int i;
00035     // Space for dynamic vectors, initialised to allocate in R/W
00036     static volatile uint32_t* vectors = (uint32_t*)NVIC_RAM_VECTOR_ADDRESS;
00037     
00038     // Copy and switch to dynamic vectors if first time called
00039     if((LPC_SYSCON->SYSMEMREMAP & 0x3) != 0x1) {     
00040       uint32_t *old_vectors = (uint32_t *)0;         // FLASH vectors are at 0x0
00041       for(i = 0; i < NVIC_NUM_VECTORS; i++) {    
00042             vectors[i] = old_vectors[i];
00043         }
00044         LPC_SYSCON->SYSMEMREMAP = 0x1; // Remaps 0x0-0x1FF FLASH block to RAM block
00045     }
00046 
00047     // Set the vector 
00048     vectors[IRQn + 16] = vector; 
00049 }
00050 
00051 uint32_t NVIC_GetVector(IRQn_Type  IRQn) {
00052     // We can always read vectors at 0x0, as the addresses are remapped
00053     uint32_t *vectors = (uint32_t*)0; 
00054 
00055     // Return the vector
00056     return vectors[IRQn + 16];
00057 }
00058