uboot 串口初始化

目录

零、概述
一、init_baudrate
二、serial_init
三、console_init_f
四、devices_init
五、console_init_r
六、打印信息
七、为什么要使用devlist，std_device[]？

零、概述

上面这张图是U-Boot中串口设备驱动的流程，从寄存器级别的设置到最后终端信息的输出。下面我们详细讲解每一个步骤。

一、init_baudrate

该函数设置了gd->bd->bi_baudrate。

static int init_baudrate (void){char tmp[64];/* long enough for environment variables */int i = getenv_r ("baudrate", tmp, sizeof (tmp));gd->bd->bi_baudrate = gd->baudrate = (i > 0)? (int) simple_strtoul (tmp, NULL, 10): CONFIG_BAUDRATE;//#define CONFIG_BAUDRATE115200  定义在/include/configs/smdk2410.c中//如果环境中没有保存，则使用宏定义的参数return (0);}

二、serial_init

UART控制器的初始化。

void serial_setbrg (void){S3C24X0_UART * const uart = S3C24X0_GetBase_UART(UART_NR);int i;unsigned int reg = 0;/* value is calculated so : (int)(PCLK/16./baudrate) -1 */reg = get_PCLK() / (16 * gd->baudrate) - 1;/* FIFO enable, Tx/Rx FIFO clear */uart->UFCON = 0x07;uart->UMCON = 0x0;/* Normal,No parity,1 stop,8 bit */uart->ULCON = 0x3;/* * tx=level,rx=edge,disable timeout int.,enable rx error int., * normal,interrupt or polling */uart->UCON = 0x245;uart->UBRDIV = reg;#ifdef CONFIG_HWFLOWuart->UMCON = 0x1; /* RTS up */#endiffor (i = 0; i < 100; i++);}/* * Initialise the serial port with the given baudrate. The settings * are always 8 data bits, no parity, 1 stop bit, no start bits. * */int serial_init (void){serial_setbrg ();//UART寄存器设置return (0);}

三、console_init_f

控制台的前期初始化。

int console_init_f (void){gd->have_console = 1;#ifdef CONFIG_SILENT_CONSOLEif (getenv("silent") != NULL)gd->flags |= GD_FLG_SILENT;#endifreturn (0);}

四、devices_init

这一部分在前面的文章已经分析过了，这里就不在叙述了。

五、console_init_r

控制台后期初始化。查看环境参数stdin,stdout,stderr中对标准IO的指定的设备名称，如果没有知道再按照环境指定的名称搜索devlist，将搜到的设备指针赋给标准IO数组stdio_devices[]。

int console_init_r (void){char *stdinname, *stdoutname, *stderrname;device_t *inputdev = NULL, *outputdev = NULL, *errdev = NULL;#ifdef CFG_CONSOLE_ENV_OVERWRITEint i;#endif /* CFG_CONSOLE_ENV_OVERWRITE *//* set default handlers at first 设置跳转表*/gd->jt[XF_getc] = serial_getc;gd->jt[XF_tstc] = serial_tstc;gd->jt[XF_putc] = serial_putc;gd->jt[XF_puts] = serial_puts;gd->jt[XF_printf] = serial_printf;/* stdin stdout and stderr are in environment 查看环境参数stdin,stdout,stderr中对标准IO的指定的设备名称*//* scan for it */stdinname  = getenv ("stdin");stdoutname = getenv ("stdout");stderrname = getenv ("stderr");if (OVERWRITE_CONSOLE == 0) { /* if not overwritten by config switch */inputdev  = search_device (DEV_FLAGS_INPUT,  stdinname);outputdev = search_device (DEV_FLAGS_OUTPUT, stdoutname);errdev    = search_device (DEV_FLAGS_OUTPUT, stderrname);}/* if the devices are overwritten or not found, use default device 按指定的名称搜索设备*/if (inputdev == NULL) {inputdev  = search_device (DEV_FLAGS_INPUT,  "serial");}if (outputdev == NULL) {outputdev = search_device (DEV_FLAGS_OUTPUT, "serial");}if (errdev == NULL) {errdev    = search_device (DEV_FLAGS_OUTPUT, "serial");}/* Initializes output console first将搜到的设备指针赋给标准IO数组stdio_devices[]，在下面会将为什么要这样做 */if (outputdev != NULL) {console_setfile (stdout, outputdev);}if (errdev != NULL) {console_setfile (stderr, errdev);}if (inputdev != NULL) {console_setfile (stdin, inputdev);}gd->flags |= GD_FLG_DEVINIT;/* device initialization completed，到此串口设备才初始化完成，这个标志会影响getc等函数 */#ifndef CFG_CONSOLE_INFO_QUIET/* Print information 打印信息*/puts ("In:    ");if (stdio_devices[stdin] == NULL) {puts ("No input devices available!\n");} else {printf ("%s\n", stdio_devices[stdin]->name);}puts ("Out:   ");if (stdio_devices[stdout] == NULL) {puts ("No output devices available!\n");} else {printf ("%s\n", stdio_devices[stdout]->name);}puts ("Err:   ");if (stdio_devices[stderr] == NULL) {puts ("No error devices available!\n");} else {printf ("%s\n", stdio_devices[stderr]->name);}#endif /* CFG_CONSOLE_INFO_QUIET */#ifdef CFG_CONSOLE_ENV_OVERWRITE/* set the environment variables (will overwrite previous env settings) */for (i = 0; i < 3; i++) {setenv (stdio_names[i], stdio_devices[i]->name);}#endif /* CFG_CONSOLE_ENV_OVERWRITE */#if 0/* If nothing usable installed, use only the initial console */if ((stdio_devices[stdin] == NULL) && (stdio_devices[stdout] == NULL))return (0);#endifreturn (0);}

六、打印信息

在最后会打印出如下信息：

In:    serial
Out:   serial
Err:   serial

这说明串口初始化完成。

七、为什么要使用devlist，std_device[]？

为了更灵活地实现标准IO重定向，任何可以作为标准IO的设备，如USB键盘，LCD屏，串口等都可以对应一个device_t的结构体变量，只需要实现getc和putc等函数，就能加入到devlist列表中去，也就可以被assign为标准IO设备stdo_device中去。如函数 int console_assign (int file, char *devname); /* Assign the console 重定向标准输入输出*/这个函数功能就是把名为devname的设备重定向为标准IO文件file(stdin,stdout,stderr)。其执行过程是在devlist中查找devname的设备，返回这个设备的device_t指针，并把指针值赋给stdo_device[file]。

int console_assign (int file, char *devname){int flag, i;/* Check for valid file */switch (file) {case stdin:flag = DEV_FLAGS_INPUT;break;case stdout:case stderr:flag = DEV_FLAGS_OUTPUT;break;default:return -1;}/* Check for valid device name */for (i = 1; i <= ListNumItems (devlist); i++) {device_t *dev = ListGetPtrToItem (devlist, i);if (strcmp (devname, dev->name) == 0) {if (dev->flags & flag)return console_setfile (file, dev);return -1;}}return -1;}

该函数是调用console_setfile设置stdo_device[]完成重定向输入输出。

static int console_setfile (int file, device_t * dev){int error = 0;if (dev == NULL)return -1;switch (file) {case stdin:case stdout:case stderr:/* Start new device */if (dev->start) {error = dev->start ();/* If it's not started dont use it */if (error < 0)break;}/* Assign the new device (leaving the existing one started) */stdio_devices[file] = dev;//这里是关键/* * Update monitor functions * (to use the console stuff by other applications) */switch (file) {case stdin:gd->jt[XF_getc] = dev->getc;gd->jt[XF_tstc] = dev->tstc;break;case stdout:gd->jt[XF_putc] = dev->putc;gd->jt[XF_puts] = dev->puts;gd->jt[XF_printf] = printf;break;}break;default:/* Invalid file ID */error = -1;}return error;}

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