串口测试主程序很简单,接下来初始化时钟。
文件clock.c:
#define CPU_AHB_APB0_CFG (*(volatile unsigned int *)0x01c20054)
#define PLL1_CFG (*(volatile unsigned int *)0x01c20000)
#define APB1_CLK_DIV_CFG (*(volatile unsigned int *)0x01c20058)
#define APB1_GATE (*(volatile unsigned int *)0x01c2006C)
void sdelay(unsigned long loops)
{
__asm__ volatile("1:\n" "subs %0, %1, #1\n"
"bne 1b":"=r" (loops):"0"(loops));
}
void clock_init(void)
{
/*AXI_DIV_1[1:0] AXI_CLK_DIV_RATIO 00:/1 AXI Clock source is CPU clock
*AHB_DIV_2[5:4] AHP_CLK_DIV_RATIO 01:/2 AHB Clock source is AXI CLOCK
*APB0_DIV_1[9:8] APB0_CLK_RATIO 00:/2 APB0 clock source is AHB2 clock
*CPU_CLK_SRC_OSC24M[17:16] CPU_CLK_SRC_SEL 01:OSC24M
*/
CPU_AHB_APB0_CFG = ((0<<0)|(0x1<<4)|(0<<8)|(1<<16));
/*bit31:PLL1_Enable 1:Enable
*bit25:EXG_MODE 0x0:Exchange mode
*bit[17:16]:PLL1_OUT_EXT_DIVP 0x0:P=1
*bit[12:8]:PLL1_FACTOR_N 0x10:Factor=16,N=16
*bit[5:4]:PLL1_FACTOR_K 0x0:K=1
*bit3:SIG_DELT_PAT_IN 0x0
*bit2:SIG_DELT_PAT_EN 0x0
*bit[1:0]PLL1_FACTOR_M 0x0:M=1
*The PLL1 output=(24M*N*K)/(M*P)=(24M*16*1)/(1*1)=384M is for the coreclk
*/
PLL1_CFG = 0xa1005000;
sdelay(200);
CPU_AHB_APB0_CFG = ((0<<0)|(0x1<<4)|(0<<8)|(2<<16));//CPU_CLK_SRC_SEL 10:PLL1
/*uart clock source is apb1,config apb1 clock*/
/*bit[25:24]:APB1_CLK_SRC_SEL 00:OSC24M
*bit[17:16]:CLK_RAT_N 0X0:1 The select clock source is pre-divided by 2^1
*bit[4:0]:CLK_RAT_M 0x0:1 The pre-devided clock is divided by(m+1)
*/
APB1_CLK_DIV_CFG = ((0<<5)|(0<<16)|(0<<24));
/*open the clock for uart0*/
/*bit16:UART0_APB_GATING 1:pass 0:mask*/
APB1_GATE = (0x1<<16);
}
初始化过程有点繁琐，对手册写了点注释，没的说，自己看手册。接下来初始化串口：
文件uart.c:
#define UART0_LCR (*(volatile unsigned int *)0x01C2800C)
#define UART0_DLH (*(volatile unsigned int *)0x01C28004)
#define UART0_DLL (*(volatile unsigned int *)0x01C28000)
#define UART0_LSR (*(volatile unsigned int *)0x01C28014)
#define UART0_THR (*(volatile unsigned int *)0x01C28000)
#define UART0_RBR (*(volatile unsigned int *)0x01C28000)
void uart_init(void)
{
/*select dll dlh*/
/*bit7:Divisor Latch Access Bit
*0:Select RX Buffer Register(RBR)/TX Holding Register(THR)and Interrupt Enable register(IER)
*1:Select Divisor Latch LS Register(DLL) and Divisor Latch MS Register(DLM)
*/
UART0_LCR = 0x80;
/*set baudrate*/
UART0_DLH = 0x0;
/*bit[7:0]:Divisor Latch Low
*baud rate=(serial clock freq)/(16*divisor)
*divisor=24M/16/115200=13.02083
*/
UART0_DLL = 0xd;
/*set line control*/
/*bit3:Parity Enable 0:parity disable 1:parity enable
*bit2:Number of stop bits
*0:1 stop bit;1:1.5 stop bits when DLS(LCR[1:0]is zero,else 2 stop bits)
*bit[1:0] Data Length Select 00:5bits;01:6bits;10:7bits;11:8bits
*/
UART0_LCR = ((0<<3)|(0<<2)|0x3);
}
char uart_getchar(void)
{
char c;
/* 查询状态寄存器，直到有有效数据 */
while (!(UART0_LSR & (1<<0)));
c = UART0_RBR; /* 读取接收寄存器的值 */
return c;
}
void uart_putchar(char c)
{
/* 查询状态寄存器，直到发送缓存为空 */
while (!(UART0_LSR & (1<<6)));
UART0_THR = c; /* 写入发送寄存器 */
return;
}