How to use Timer driver

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1. Introducation
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ADSP21535 has three Timers(Timer0, Timer1, Timer2) each of which 
has three modes:

	PWM(Pulse Width Modulation)
	CAP(Pulse Width Count and Capture) 
	ECLK (External Event Counter) 

The Timer device major/minor numbers are: 
timer device      major             minor
Timer1             10                101
Timer2             10                102
Timer3             10                103

The timer0 device name is /dev/timer0, the timer1 device name is 
/dev/timer1, and the timer2 device name is /dev/timer2.

When the read function is called, the application is locked 
until the timer interrupt is generated, and the timer device 
information is returned.

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2. Timer device information data structure
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struct timer_info {
unsigned short mode;
unsigned short status;
unsigned long  width;
unsigned long  period;
}

mode: save the timer device work mode.
    ADSP_PWM_MODE  = PWM(Pulse Width Modulation) mode
    ADSP_CAP_MODE  = CAP(Pulse Width Count and Capture) mode
    ADSP_ECLK_MODE = ECLK(External Event Counter) mode

status: same as the timer configuration register, and the status 
are composed by the following bits.
    CF_PULSE_HI    = Positive action pulse
    CF_PERIOD_CNT  = Count to end of period
    CF_UART_SEL    = UARTy RX selected
    CF_INT_EN      = Enable interrupt request

width:  same as the device width register.

period: same as the device period register.

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3. system call
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The timer device driver is designed as a standard character 
driver.
The following system calls are supported.
The device can be opened by only one process(thread) at a time.

3.1 open: The standard open function call.
int open("/dev/timerx", int oflag, /* mode_t mode */...);

The open function is used to establish the connection between the Timer
device with a file descriptor.
- oflag:
  O_RDONLY   Open for reading only
  O_WRONLY   Open for writing only
  O_RDWR     Open for reading and writing

USAGE(Timer1):
--------------
int fd;

fd = open("/dev/timer1", O_RDONLY, 0);
...
close(fd);

3.2 close: The standard open function call.
int close(int file_handler);

The close function is used to disconnect the Timer device with the relevant 
file descriptor.

USAGE(Timer1):
--------------
int fd;

fd = open("/dev/timer1", O_RDONLY, 0);
...
close(fd);

3.3 ioctl: the standard ioctl function call(refer to section 3).
int ioctl(int file_handler, int request, /* arg */...);

The ioctl command is used to configure the Timer device.

USAGE(Timer1):
--------------
int fd;
int ret;
struct timer_info tinfo;

fd = open("/dev/timer1", O_RDONLY, 0);
......
// the ioctl command CMD_TIMER_SETMODE is used to configure the timer1 device.
// about the detail ioctl command, refer to section 4.
ret = ioctl(fd, CMD_TIMER_SETMODE, &tinfo);
...
close(fd);

3.4 read:  the standard read function call.
ssize_t read(int file_handler, viod *buf, size_t nbytes);

The timer device read functions only support the timer information
read operations. When the read fucntion is called, 
the timer device information (struct timer_info) is returned.

USAGE(Timer1):
--------------
int fd;
int ret;
struct timer_info tinfo;

fd = open("/dev/timer1", O_RDONLY, 0);
// call the read function to get the Timer parameters.
ret = read(fd, &tinfo, sizeof(tinfo));
......
close(fd);

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4. Timer deivce ioctl
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CMD_TIMER_ENABLE:  This ioctl does not need an argument, and it 
                   can be used to enable the timer device.

CMD_TIMER_DISABLE: This ioctl does not need an argument, and it 
                   can be used to disable the timer device.

CMD_TIMER_RESET:   This ioctl does not need an argument, and it 
                   can be used to disable the timer device and 
                   clear all timer current information.   
 
CMD_TIMER_SETMODE: This ioctl needs one argument 
                   (struct timer_info *), which can be used to 
                   set the timer device.

CMD_TIMER_GETINFO: This ioctl needs one argument 
                   (struct timer_info *), which can be used to 
                   get the timer device information.

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5. Caution
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