uboot串口初始化

uboot下的串口初始化分多个步骤完成，在uboot初始化序列init_sequence[]中有三个串口相关的初始化函数。init_baudrate是用来设置串口的波特率，它首先会去uboot的环境变量里面找波特率的定义，如果找到就赋值给全局变量中的baudrate，如果环境变量中没有定义，则使用一个默认的配置值。serial_init跟具体的平台相关，以marvell平台为例，该函数定义在mv_serial.c中。该函数首先根据波特率计算出clock_divisor的值，然后调用mvUartInit()对串口硬件进行初始化。在mvUartInit中就是直接把初始的参数写到串口的寄存器中，从而完成硬件的初始化工作。console_init_f是console初始化的第一阶段，就是设置了全局变量中的have_console变量。

init_fnc_t *init_sequence[] = {<span style="white-space:pre"></span>……init_baudrate,/* initialze baudrate settings */serial_init,/* serial communications setup */console_init_f,/* stage 1 init of console */<span style="white-space:pre"></span>……};

static int init_baudrate (void){DECLARE_GLOBAL_DATA_PTR;uchar 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;return (0);}

MV_VOID mvUartInit(MV_U32 port, MV_U32 baudDivisor, MV_UART_PORT* base){volatile MV_UART_PORT *pUartPort;#if defined(MV_UART_OVER_PEX_WA) || defined(MV_UART_OVER_PCI_WA)uartBase[port] = pUartPort = (volatile MV_UART_PORT *)(base);return;#elseuartBase[port] = pUartPort = (volatile MV_UART_PORT *)base;pUartPort->ier = 0x00;pUartPort->lcr = LCR_DIVL_EN;           /* Access baud rate */pUartPort->dll = baudDivisor & 0xff;    /* 9600 baud */pUartPort->dlm = (baudDivisor >> 8) & 0xff;pUartPort->lcr = LCR_8N1;               /* 8 data, 1 stop, no parity *//* Clear & enable FIFOs */pUartPort->fcr = FCR_FIFO_EN | FCR_RXSR | FCR_TXSR;return;#endif}

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

第四个初始化阶段在devices_init()中，devices_init()完成的工作就相当于uboot下的设备管理机制，把各类设备按照特定的格式添加到一个设备链表devlist中去。对串口设备的初始化工作在drv_system_init()中，该函数首先把设备名字设为serial，并把设备的flags设为DEV_FLAGS_OUTPUT | DEV_FLAGS_INPUT | DEV_FLAGS_SYSTEM，然后为devict_t中对应的操作函数进行赋值操作，主要实现输入输出的功能，具体的实现函数也跟平台相关。比如dev.putc被定义为serial_putc()，在marvell的平台中该函数定义在mv_serial.c中，它直接调用mvUartPutc()来实现输出操作，在mvUartPutc()中直接把要输出的值赋给输出寄存器。初始化好设备描述符后，调用device_register()把设备加到全局的设备链表中。

static void drv_system_init (void){device_t dev;memset (&dev, 0, sizeof (dev));strcpy (dev.name, "serial");dev.flags = DEV_FLAGS_OUTPUT | DEV_FLAGS_INPUT | DEV_FLAGS_SYSTEM;#ifdef CONFIG_SERIAL_SOFTWARE_FIFOdev.putc = serial_buffered_putc;dev.puts = serial_buffered_puts;dev.getc = serial_buffered_getc;dev.tstc = serial_buffered_tstc;#elsedev.putc = serial_putc;dev.puts = serial_puts;dev.getc = serial_getc;dev.tstc = serial_tstc;#endifdevice_register (&dev);#ifdef CFG_DEVICE_NULLDEVmemset (&dev, 0, sizeof (dev));strcpy (dev.name, "nulldev");dev.flags = DEV_FLAGS_OUTPUT | DEV_FLAGS_INPUT | DEV_FLAGS_SYSTEM;dev.putc = nulldev_putc;dev.puts = nulldev_puts;dev.getc = nulldev_input;dev.tstc = nulldev_input;device_register (&dev);#endif}

serial_putc(const char c){#if defined(CONFIG_MV_SMP) || (defined(MV78XX0) && defined(MV78200))        if (c == '\n')                mvUartPutc((whoAmI())%2, '\r');        mvUartPutc((whoAmI())%2, c);#elseif (c == '\n')mvUartPutc(CFG_DUART_CHAN, '\r');mvUartPutc(CFG_DUART_CHAN, c);#endif}

MV_VOIDmvUartPutc(MV_U32 port, MV_U8 c){volatile MV_UART_PORT *pUartPort = uartBase[port];while ((pUartPort->lsr & LSR_THRE) == 0) ;pUartPort->thr = c;return;}

最后一个初始化阶段在console_init_r()中，在该函数中，首先定义两个变量inputdev和outputdev，并初始化为NULL，然后会去遍历全局的设备列表，如果有某个设备的flags为DEV_FLAGS_INPUT，则把该设备赋值给inputdev，同样，如果有某个设备的flags为DEV_FLAGS_OUTPUT，则把它赋值给outputdev。如果有找到这样的inputdev和outputdev，则调用console_setfile()来设置标准输入，标准输入以及错误输出的文件描述符。在console_setfile()中，主要是对stdio_devices[]数组进行赋值操作，该数组有三个元素，对应输入，输出以及错误文件描述符，所以就是把具体的设备跟这三个文件描述绑定在一起。

int console_init_r (void){DECLARE_GLOBAL_DATA_PTR;device_t *inputdev = NULL, *outputdev = NULL;int i, items = ListNumItems (devlist);#ifdef CONFIG_SPLASH_SCREEN/* suppress all output if splash screen is enabled and we have   a bmp to display                                            */if (getenv("splashimage") != NULL)outputdev = search_device (DEV_FLAGS_OUTPUT, "nulldev");#endif#ifdef CONFIG_SILENT_CONSOLE/* Suppress all output if "silent" mode requested*/if (gd->flags & GD_FLG_SILENT)outputdev = search_device (DEV_FLAGS_OUTPUT, "nulldev");#endif/* Scan devices looking for input and output devices */for (i = 1;     (i <= items) && ((inputdev == NULL) || (outputdev == NULL));     i++    ) {device_t *dev = ListGetPtrToItem (devlist, i);if ((dev->flags & DEV_FLAGS_INPUT) && (inputdev == NULL)) {inputdev = dev;}if ((dev->flags & DEV_FLAGS_OUTPUT) && (outputdev == NULL)) {outputdev = dev;}}/* Initializes output console first */if (outputdev != NULL) {console_setfile (stdout, outputdev);console_setfile (stderr, outputdev);}/* Initializes input console */if (inputdev != NULL) {console_setfile (stdin, inputdev);}gd->flags |= GD_FLG_DEVINIT;/* device initialization completed */#ifndef CFG_CONSOLE_INFO_QUIET/* Print information */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 *//* Setting environment variables */for (i = 0; i < 3; i++) {setenv (stdio_names[i], stdio_devices[i]->name);}#if 0/* If nothing usable installed, use only the initial console */if ((stdio_devices[stdin] == NULL) && (stdio_devices[stdout] == NULL))return (0);#endifreturn (0);}

static int console_setfile (int file, device_t * dev){DECLARE_GLOBAL_DATA_PTR;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;/* * 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;}

前面三个阶段主要是对硬件的初始化，后面两个阶段主要是实现串口操作功能的初始化，因为设置好标准输入输出后，我们就可以从串口看到uboot的加载和调试信息。看一下uboot下的printf()函数，该函数先调用vsprintf()对输出内容进行格式化处理，然后调用puts()输出内容。在puts()中，根据GD_FLG_DEVINIT标记进行不同的处理，这个标记在console_init_r()有被设置，所以调用fputs()函数，而fputs()就是直接调用stdio_devices[]数组中的标准输出设备来输出内容，这个设备就是在console_init_r()中绑定的。

void printf (const char *fmt, ...){va_list args;uint i;char printbuffer[CFG_PBSIZE];va_start (args, fmt);/* For this to work, printbuffer must be larger than * anything we ever want to print. */i = vsprintf (printbuffer, fmt, args);va_end (args); /* Print the string */puts (printbuffer);}

void puts (const char *s){DECLARE_GLOBAL_DATA_PTR;#ifdef CONFIG_SILENT_CONSOLEif (gd->flags & GD_FLG_SILENT)return;#endifif (gd->flags & GD_FLG_DEVINIT) {/* Send to the standard output */fputs (stdout, s);} else {/* Send directly to the handler */serial_puts (s);}}

void fputs (int file, const char *s){if (file < MAX_FILES)stdio_devices[file]->puts (s);}