设置T113串口波特率为1M

[lansecd]

用UART5非标准波率通信，波特率设置为1M，应用程序中串口配置如下：

	//open uart
	fd = open("/dev/ttyS5", O_RDWR);
	if (fd < 0)
	{
		printf("open failed\n");
		return -1;
	}

	/*set baudrate*/
	tcgetattr(fd, &options);
	cfsetispeed(&options, B1000000);
	cfsetospeed(&options, B1000000);
	options.c_cflag |= (CLOCAL | CREAD);

	/*set databits*/
	options.c_cflag &= ~CSIZE;
	options.c_cflag |= CS8;

	/*set crc*/
	options.c_cflag &= ~PARENB;
	options.c_cflag &= ~CSTOPB;

	/*set stopbits*/
	options.c_cflag &= ~CSTOPB; 

	/*set parity*/
	options.c_cflag &= ~PARENB;

	options.c_lflag  &= ~(ICANON | ECHO | ECHOE | ISIG);  
	options.c_oflag  &= ~OPOST;  

	options.c_cc[VTIME] = 0;
	options.c_cc[VMIN] = 0;

系统启动后，启动应用程序，发现报如下错误：

[  241.774864] sw_uart_check_baudset()837 - uart5, select set 5, baud 1000000, uartclk 24000000 beyond rance[31000000, 120000000]

发现串口的时钟源为24MHZ，不支持该波特率设置，于是查看Linux_UART_开发指南.pdf，查找波特率的修改方法，具体可以查看该开发指南，这里贴出修改方法。

修改设备树，修改串口的时钟源
/lichee/linux-5.4/arch/arm/boot/dts/sun8iw20p1.dtsi

uart5: uart@2501400 {
	compatible = "allwinner,sun8i-uart";
	device_type = "uart5";
	reg = <0x0 0x02501400 0x0 0x400>;
	interrupts = <GIC_SPI 7 IRQ_TYPE_LEVEL_HIGH>;
	sunxi,uart-fifosize = <256>;
	clocks = <&ccu CLK_BUS_UART5>;
	clock-names = "uart5";
	resets = <&ccu RST_BUS_UART5>;
	uart5_port = <5>;
	uart5_type = <2>;
	status = "disabled";
};

编译，烧录，启动发现终端乱码，这里把终端串口的时钟源也进行修改

uart0: uart@2500000 {
	compatible = "allwinner,sun8i-uart";
	device_type = "uart0";
	reg = <0x0 0x02500000 0x0 0x400>;
	interrupts = <GIC_SPI 2 IRQ_TYPE_LEVEL_HIGH>;
	sunxi,uart-fifosize = <64>;
	clocks = <&ccu CLK_BUS_UART0>,<&ccu CLK_APB1>,<&ccu CLK_PSI_AHB>;
	clock-frequency = <50000000>;
	clock-names = "uart0";
	resets = <&ccu RST_BUS_UART0>;
	uart0_port = <0>;
	uart0_type = <2>;
	status = "disabled";
};

再次，烧录，启动，运行程序，进行数据收发测试

[lansecd]

@lansecd 在 设置T113串口波特率为1M 中说：

uart5: uart@2501400 {
compatible = "allwinner,sun8i-uart";
device_type = "uart5";
reg = <0x0 0x02501400 0x0 0x400>;
interrupts = <GIC_SPI 7 IRQ_TYPE_LEVEL_HIGH>;
sunxi,uart-fifosize = <256>;
clocks = <&ccu CLK_BUS_UART5>;
clock-names = "uart5";
resets = <&ccu RST_BUS_UART5>;
uart5_port = <5>;
uart5_type = <2>;
status = "disabled";
};

uart5: uart@2501400 {
	compatible = "allwinner,sun8i-uart";
	device_type = "uart5";
	reg = <0x0 0x02501400 0x0 0x400>;
	interrupts = <GIC_SPI 7 IRQ_TYPE_LEVEL_HIGH>;
	sunxi,uart-fifosize = <256>;
	clocks = <&ccu CLK_BUS_UART5>,<&ccu CLK_APB1>,<&ccu CLK_PSI_AHB>;
        clock-frequency = <50000000>;
	clock-names = "uart5";
	resets = <&ccu RST_BUS_UART5>;
	uart5_port = <5>;
	uart5_type = <2>;
	status = "disabled";
};