RTEMS 的 AT91SAM9260 移植(5): 调试串口驱动

其实到这里，只要能保证编译通过，再修改一下链接脚本，其实已经可以跑在at9260的系统上了。因为我没有仿真器，不知道程序的状态，所以必须撰写调试串口的驱动。

RTEMS 的调试串口并没有采用中断输出的方式，而是采用查询输出的方式。相对来说比较容易。

RTEMS里有两个打印函数：

 

printf 和 printk

 

printf是由库支持的打印函数，内部比较复杂，主要用于应用程序级别的打印，不能用于内核和中断的打印，特别是中断中不能使用该函数，否则会引起死机。

printk是由rtems的调试打印函数，主要用于内核和中断的打印。任务级别也可以调用，但是最好不要这样做。

 

printk是调用 BSP_output_char 这个函数指针完成字符的输出。

可以在c/src/lib/lbicpu/arm/at91sam9260/dbgu/Dbgu.c中的末尾的

 

static void _BSP_put_char( char c ) {
    dbgu_write_polled(0, c);
}

 

BSP_output_char_function_type BSP_output_char = _BSP_put_char;

 

那么就是说，printk实际上是调用调试串口驱动完成字符的输出。

既然调用调试串口输出，必须等调试串口初始化完成以后才能输出。

 

start.S执行完毕后，是跳转到 bootcard 函数中继续执行，bootcard 要完成对内核数据的初始化后，才调用IO的初始化，这时串口的驱动才能工作。也就是说，想在bootcard运行调试串口初始化以前，看到printk的输出，基本上是不可能的。

 

如果你真的想这个时候也能看到printk的输出，只能提前初始化串口驱动了。

我的做法是，dbgu_write 函数内部会检查调试串口有没有被初始化，如果没有被初始化，先初始化再输出字符。那么这样，即使在start.S汇编文件里调用printk，也是能看到输出的。

 

这里还要注意一个问题就是调试串口的波特率，调试串口的波特率是通过函数BSP_get_baud获得，

这个函数在c/src/lib/libbsp/arm/at9260/include/bsp.h中。

 

 

另外就是修改 c/src/lib/libbsp/arm/at9260/console/uarts.c的代码。

这里的改动主要是一些配置和寄存器，没有什么好讲的。

 

下面是dbgu.c的源代码：

/* * Console driver for AT91SAM9260 DBGU port * */ #include <bsp.h> #include <rtems/libio.h> #include <termios.h> #include <at91sam9260.h> #include <rtems/bspIo.h> #include <libchip/serial.h> #include <libchip/sersupp.h> #define AT91SAM9260_DBGU_NUM 1 static volatile int _gIsInitDbgu[AT91SAM9260_DBGU_NUM] = {0}; volatile int dbg_dly; /* static function prototypes */ static int dbgu_first_open(int major, int minor, void *arg); static int dbgu_last_close(int major, int minor, void *arg); static int dbgu_read(int minor); static int dbgu_write(int minor, const char *buf, int len); static void dbgu_init(int minor); static void dbgu_write_polled(int minor, char c); static int dbgu_set_attributes(int minor, const struct termios *t); /* Pointers to functions for handling the UART. */ console_fns dbgu_fns = { libchip_serial_default_probe, dbgu_first_open, dbgu_last_close, dbgu_read, dbgu_write, dbgu_init, dbgu_write_polled, /* not used in this driver */ dbgu_set_attributes, FALSE /* TRUE if interrupt driven, FALSE if not. */ }; /*********************************************************************/ /* Functions called via callbacks (i.e. the ones in uart_fns */ /*********************************************************************/ /* * This is called the first time each device is opened. Since * the driver is polled, we don't have to do anything. If the driver * were interrupt driven, we'd enable interrupts here. */ static int dbgu_first_open(int major, int minor, void *arg) { return 0; } /* * This is called the last time each device is closed. Since * the driver is polled, we don't have to do anything. If the driver * were interrupt driven, we'd disable interrupts here. */ static int dbgu_last_close(int major, int minor, void *arg) { return 0; } /* * Read one character from UART. * * return -1 if there's no data, otherwise return * the character in lowest 8 bits of returned int. */ static int dbgu_read(int minor) { char c; console_tbl *console_entry; AT91S_DBGU *dbgu; if ((minor < AT91SAM9260_DBGU_NUM) && (0 == _gIsInitDbgu[minor])) dbgu_init(minor); console_entry = BSP_get_uart_from_minor(minor); if (console_entry == NULL) { return -1; } dbgu = (AT91S_DBGU *)console_entry->ulCtrlPort1; if (!(dbgu->DBGU_CSR & AT91C_US_RXRDY)) { return -1; } c = dbgu->DBGU_RHR & 0xff; return c; } /* * Write buffer to UART * * return 1 on success, -1 on error */ static int dbgu_write(int minor, const char *buf, int len) { int i, x; char c; console_tbl *console_entry; AT91S_DBGU *dbgu; if ((minor < AT91SAM9260_DBGU_NUM) && (0 == _gIsInitDbgu[minor])) dbgu_init(minor); console_entry = BSP_get_uart_from_minor(minor); if (console_entry == NULL) { return -1; } dbgu = (AT91S_DBGU *)console_entry->ulCtrlPort1; for (i = 0; i < len; i++) { /* Wait for fifo to have room */ while(1) { if (dbgu->DBGU_CSR & AT91C_US_TXRDY) { break; } } c = (char) buf[i]; dbgu->DBGU_THR = c; /* the TXRDY flag does not seem to update right away (is this true?) */ /* so we wait a bit before continuing */ for (x = 0; x < 10; x++) { dbg_dly++; /* using a global so this doesn't get optimized out */ } } return 1; } /* Set up the UART. */ static void dbgu_init(int minor) { console_tbl *console_entry; AT91S_DBGU *dbgu; if ((minor >= AT91SAM9260_DBGU_NUM) || (_gIsInitDbgu[minor] > 0)) return ; console_entry = BSP_get_uart_from_minor(minor); if (console_entry == NULL) { return; } _gIsInitDbgu[minor] = 1; dbgu = (AT91S_DBGU *)console_entry->ulCtrlPort1; AT91C_BASE_PIOB->PIO_IDR = (1<<14) | (1<<15); AT91C_BASE_PIOB->PIO_ASR = (1<<14) | (1<<15); AT91C_BASE_PIOB->PIO_BSR = 0; AT91C_BASE_PIOB->PIO_PDR = (1<<14) | (1<<15); AT91C_BASE_PIOB->PIO_PPUDR = (1<<14) | (1<<15); /* Clear error bits, and reset */ dbgu->DBGU_CR = (AT91C_US_RSTSTA | AT91C_US_RSTTX | AT91C_US_RSTRX); /* Clear pending interrupts */ dbgu->DBGU_IDR = (AT91C_US_RXRDY | AT91C_US_TXRDY | AT91C_US_ENDRX | AT91C_US_ENDTX | AT91C_US_OVRE | AT91C_US_FRAME | AT91C_US_PARE | AT91C_US_TXEMPTY | AT91C_US_TXBUFE | AT91C_US_RXBUFF | AT91C_US_COMM_TX | AT91C_US_COMM_RX); dbgu->DBGU_IMR = 0; /* Set port to no parity, no loopback */ dbgu->DBGU_MR = AT91C_US_PAR_NONE | AT91C_US_CHMODE_NORMAL; /* Set the baud rate */ dbgu->DBGU_BRGR = (at91sam9260_get_mck() / 16) / BSP_get_baud(); /* Enable the DBGU */ dbgu->DBGU_CR = (AT91C_US_RXEN | AT91C_US_TXEN); } /* I'm not sure this is needed for the shared console driver. */ static void dbgu_write_polled(int minor, char c) { dbgu_write(minor, &c, 1); } /* This is for setting baud rate, bits, etc. */ static int dbgu_set_attributes(int minor, const struct termios *t) { return 0; } /***********************************************************************/ /* * The following functions are not used by TERMIOS, but other RTEMS * functions use them instead. */ /***********************************************************************/ /* * Read from UART. This is used in the exit code, and can't * rely on interrupts. */ int dbgu_poll_read(int minor) { return dbgu_read(minor); } /* * Write a character to the console. This is used by printk() and * maybe other low level functions. It should not use interrupts or any * RTEMS system calls. It needs to be very simple */ static void _BSP_put_char( char c ) { dbgu_write_polled(0, c); } BSP_output_char_function_type BSP_output_char = _BSP_put_char;

 

 

下面是uarts.c的代码：

/* * Console driver for AT9260 * * This driver uses the shared console driver in * ...../libbsp/shared/console.c * */ #include <bsp.h> #include <rtems/libio.h> #include <termios.h> #include <rtems/bspIo.h> #include <at91sam9260.h> #include <libchip/serial.h> #include <libchip/sersupp.h> /* How many serial ports? */ #define NUM_DEVS 1 /* These are used by code in console.c */ unsigned long Console_Port_Count = NUM_DEVS; console_data Console_Port_Data[NUM_DEVS]; /* rtems console uses the following minor number */ rtems_device_minor_number Console_Port_Minor = 0; extern console_fns dbgu_fns; /* * There's one item in array for each UART. * * Some of these fields are marked "NOT USED". They are not used * by console.c, but may be used by drivers in libchip * * when we add other types of UARTS we will need to move this * structure to a generic uart.c file with only this in it */ console_tbl Console_Port_Tbl[] = { { "/dev/console", /* sDeviceName */ SERIAL_CUSTOM, /* deviceType */ &dbgu_fns, /* pDeviceFns */ NULL, /* deviceProbe */ NULL, /* pDeviceFlow */ 0, /* ulMargin - NOT USED */ 0, /* ulHysteresis - NOT USED */ NULL, /* pDeviceParams */ AT91C_BASE_DBGU, /* ulCtrlPort1 - Pointer to DBGU regs */ 0, /* ulCtrlPort2 - NOT USED */ 0, /* ulDataPort - NOT USED */ NULL, /* getRegister - NOT USED */ NULL, /* setRegister - NOT USED */ NULL, /* getData - NOT USED */ NULL, /* setData - NOT USED */ 0, /* ulClock - NOT USED */ 0 /* ulIntVector - NOT USED */ }}; console_tbl *BSP_get_uart_from_minor(int minor) { return &Console_Port_Tbl[minor]; } 

 

 

至此，搞定调试串口驱动。