S3C2440有三个时钟：FCLK for CPU, HCLK for the AHB bus peripherals, and PCLK for the APB bus peripherals
S3C2440系统时钟配置：
首先配置PLL控制寄存器
设置MPLLCON寄存器
unsigned int FCLK;
unsigned int HCLK;
unsigned int PCLK;
unsigned int UCLK;
#define FIN 12000000
1 void ChangeMPllValue(int mdiv,int pdiv,int sdiv)//设置FCLK的值 2 { 3 MPLLCON = (mdiv<<12) | (pdiv<<4) | sdiv; 4 }
设置UPLLCON寄存器
1 void ChangeUPllValue(int mdiv,int pdiv,int sdiv)//设置UCLK的值,给USB供节拍 2 { 3 UPLLCON = (mdiv<<12) | (pdiv<<4) | sdiv; 4 }
设置时钟分频器控制寄存器CLKDIVN
1 void ChangeClockDivider(int hdivn,int pdivn)//设置FCLK，HCLK，PCLK的时钟比例,以及摄像头时钟比例 2 { 3 // hdivn,pdivn FCLK:HCLK:PCLK 4 // 0,0 1:1:1 5 // 0,1 1:1:2 6 // 1,0 1:2:2 7 // 1,1 1:2:4 8 // 2,0 1:4:4 9 // 2,1 1:4:8 10 // 3,0 1:3:3 11 // 3,1 1:3:6 12 CLKDIVN = (hdivn<<1) | pdivn; 13 14 if (hdivn == 2) 15 CAMDIVN = (CAMDIVN & ~(1<<9));
16 if (hdivn == 3) 17 CAMDIVN = (CAMDIVN & ~(1<<8));
18 }
计算具体的FCLK，HCLK，PCLK，UCLK的大小
1 void CalcBusClk(void) //计算具体的FCLK，HCLK，PCLK，UCLK的大小 2 { 3 unsigned int val,UPLL; 4 unsigned char m, p, s; 5 val = MPLLCON; 6 m = (val >> 12) & 0xff; 7 p = (val >> 4) & 0x3f; 8 s = val & 3; 9 10 FCLK = ((m+8)*FIN*2)/((p+2)*(1<<s)); 11 12 val = CLKDIVN; 13 m = (val >> 1) & 3; 14 p = val & 1; 15 val = CAMDIVN; 16 s = val >> 8; 17 18 switch (m) 19 { 20 case 0: 21 HCLK = FCLK; 22 break; 23 case 1: 24 HCLK = FCLK >> 1; 25 break; 26 case 2: 27 if(s & 2) 28 HCLK = FCLK >> 3; 29 else 30 HCLK = FCLK >> 2; 31 break; 32 case 3: 33 if(s & 1) 34 HCLK = FCLK / 6; 35 else 36 HCLK = FCLK / 3; 37 break; 38 } 39 if(p) 40 PCLK = HCLK >> 1; 41 else 42 PCLK = HCLK; 43 44 val = UPLLCON; 46 m = (val >> 12) & 0xff; 47 p = (val >> 4) & 0x3f; 48 s = val & 3; 49 UPLL = ((m+8)*FIN)/((p+2)*(1<<s)); 50 UCLK = (CLKDIVN&8)?(UPLL>>1):UPLL; 51 }