Linux porting on different platform HowTo(4)

修改完我之前講過的irq,timer後,渡過了一段console沒有字的debug時間,從頭到尾都用ICE去trace是很悶的,現下我把console的程式碼加上,讓console跑點字出來吧

Kernel所有的訊息都是印在console上的,所以在kernel用printk其實等於直接把buffer content倒在console

但user space的application可不是這樣,當printf印訊息時,其實是透過tty driver呼叫我們的serial driver然後請serial driver幫忙印字

藉由上面的介紹,大概瞭解console driver會用到serial driver的write函式,而serial driver也必需跟tty driver註冊自己

所以serial driver要幹的事有兩件
(1)寫console api
(2)註冊tty driver

詳細的code我不在這邊介紹,我只大略說一下linux driver的寫法
(1)先找一個小,且架構清楚的driver骨架,像我就是用4510的serial driver來修改成2410可用的serial driver
(2)把函式內的程式碼全部清掉,只剩下函式宣告
(3)根據data sheet和參考程式來填寫我們的程式

底下是qt2410 console程式的部份程式碼,只要完成這個部份,kernel就會吐訊息出來了

#ifdef CONFIG_SERIAL_QT2410_CONSOLE
/************** console driver *****************/
 
static void __qt2410_console_write(struct console *co, const char *s, u_int count)
{
    struct uart_port *port = &__qt2410_ports[co->index];
 
    __xmit_string( port, s, count);
}
 
static int __init __qt2410_console_setup(struct console *co, char *options)
{
    struct uart_port *port;
    int baud = 115200;
    int bits = 8;
    int parity = 'n';
    int flow = 0;
 
    /*
     * Check whether an invalid uart number has been specified, and
     * if so, search for the first available port that does have
     * console support.
     */
    port = uart_get_console(__qt2410_ports, UART_NR, co);
 
//    _DPRINTK("using port = 0x%08x", (unsigned int) port);
 
    if (options)
        uart_parse_options(options, &baud, &parity, &bits, &flow);
 
    __qt2410_init(port, baud);
 
    return uart_set_options(port, co, baud, parity, bits, flow);
}
 
//extern struct uart_driver __qt2410_driver;
static struct console __qt2410_console =
{
    name:           "ttySAC",
    write:        __qt2410_console_write,
    device:        uart_console_device,
    setup:        __qt2410_console_setup,
    flags:        CON_PRINTBUFFER,
    index:        -1,
    data:           &__qt2410_driver,
};
 
static int __init __qt2410_console_init(void)
{
    register_console(&__qt2410_console);
    return 0;
}
 
console_initcall(__qt2410_console_init);
 
#endif
 
 
static struct uart_driver __qt2410_driver =
{
    owner:           THIS_MODULE,
    driver_name:     __DRIVER_NAME,
    dev_name:        "ttySAC",
    major:           TTY_MAJOR,
    minor:           64,
    nr:              UART_NR,
#ifdef CONFIG_SERIAL_QT2410_CONSOLE
    cons:            &__qt2410_console,
#endif
};

下圖是開機的過程