lowlevelinit.c

Atmel 公司提供的另一个参考代码

//  ----------------------------------------------------------------------------
//           ATMEL Microcontroller Software Support  -  ROUSSET  -
//  ----------------------------------------------------------------------------
//   The software is delivered "AS IS" without warranty or condition of any
//   kind, either express, implied or statutory. This includes without
//   limitation any warranty or condition with respect to merchantability or
//   fitness for any particular purpose, or against the infringements of
//   intellectual property rights of others.
//  ----------------------------------------------------------------------------
//   File Name           : Cstartup_SAM7.c
//   Object              : Low level initializations written in C for IAR tools
//   1.0   08/Sep/04 JPP : Creation
//   1.10  10/Sep/04 JPP : Update AT91C_CKGR_PLLCOUNT filed
//  ----------------------------------------------------------------------------


// Include the board file description
#include "AT91SAM7S256.h"
#include "Board.h"

// The following functions must be write in ARM mode this function called directly
// by exception vector
extern void AT91F_Spurious_handler(void);
extern void AT91F_Default_IRQ_handler(void);
extern void AT91F_Default_FIQ_handler(void);

//*----------------------------------------------------------------------------
//* \fn    AT91F_LowLevelInit
//* \brief This function performs very low level HW initialization
//*        this function can be use a Stack, depending the compilation
//*        optimization mode
//*----------------------------------------------------------------------------
void LowLevelInit(void)
{
 	int            i;
 	AT91PS_PMC     pPMC = AT91C_BASE_PMC;
 
    //* Set Flash Wait sate
	//  Single Cycle Access at Up to 30 MHz, or 40
	//  if MCK = 48054841 I have 50 Cycle for 1 usecond ( flied MC_FMR->FMCN
	//  result: AT91C_MC_FMR = 0x00320100  (MC Flash Mode Register)
	AT91C_BASE_MC->MC_FMR = ((AT91C_MC_FMCN)&(50 <<16)) | AT91C_MC_FWS_1FWS;

    //* Watchdog Disable
    // result: AT91C_WDTC_WDMR = 0x00008000  (Watchdog Mode Register)
	AT91C_BASE_WDTC->WDTC_WDMR= AT91C_WDTC_WDDIS;

	//* Set MCK at 48 054 841
    // 1 Enabling the Main Oscillator:
	// SCK = 1/32768 = 30.51 uSecond
	// Start up time = 8 * 6 / SCK = 56 * 30.51 = 1,46484375 ms
	// result: AT91C_CKGR_MOR = 0x00000601  (Main Oscillator Register) 
	pPMC->PMC_MOR = (( AT91C_CKGR_OSCOUNT & (0x06 <<8) | AT91C_CKGR_MOSCEN ));
	
	// Wait the startup time
	while(!(pPMC->PMC_SR & AT91C_PMC_MOSCS));
	
	// PMC Clock Generator PLL Register setup
	//
	// The following settings are used:  DIV = 14
	//                                   MUL = 72
	//                                   PLLCOUNT = 10
	//
	// Main Clock (MAINCK from crystal oscillator) = 18432000 hz (see AT91SAM7-EK schematic)
	// MAINCK / DIV = 18432000/14 = 1316571 hz
	// PLLCK = 1316571 * (MUL + 1) = 1316571 * (72 + 1) = 1316571 * 73 = 96109683 hz
	//
	// PLLCOUNT = number of slow clock cycles before the LOCK bit is set 
	//            in PMC_SR after CKGR_PLLR is written.
	//
	// PLLCOUNT = 10
	//
	// OUT = 0 (not used)
	// result: AT91C_CKGR_PLLR = 0x00000000480A0E   (PLL Register) 
	pPMC->PMC_PLLR = ((AT91C_CKGR_DIV & 14) |
                      (AT91C_CKGR_PLLCOUNT & (10<<8)) |
                      (AT91C_CKGR_MUL & (72<<16)));

	// Wait the startup time (until PMC Status register LOCK bit is set)
 	while(!(pPMC->PMC_SR & AT91C_PMC_LOCK));
 	
	// PMC Master Clock (MCK) Register setup
	//
	// CSS  = 3  (PLLCK clock selected)
	//
	// PRES = 1  (MCK = PLLCK / 2) = 96109683/2 = 48054841 hz
	//
	// Note: Master Clock  MCK = 48054841 hz  (this is the CPU clock speed)
	// result:  AT91C_PMC_MCKR = 0x00000007  (Master Clock Register)
	pPMC->PMC_MCKR = AT91C_PMC_CSS_PLL_CLK | AT91C_PMC_PRES_CLK_2;
	
	// Set up the default interrupts handler vectors
	AT91C_BASE_AIC->AIC_SVR[0] = (int) AT91F_Default_FIQ_handler;
	for (i=1;i < 31; i++)
	{
	    AT91C_BASE_AIC->AIC_SVR[i] = (int) AT91F_Default_IRQ_handler;
	}
	AT91C_BASE_AIC->AIC_SPU  = (int) AT91F_Spurious_handler;

}