Using the PWM output of Timer0 in S3C2440 to drive the buzzer

There are five 16-bit timers in S3C2440, timer0, timer1, timer2, timer3 and timer4. Among them, only timer4 is an internal timer without output pins. Therefore, only timers 0, 1, 2, and 3 have pulse width modulation (PWM) function. Timer 0 has a dead zone generator for high current devices. (Hereinafter, timer 0 is used as an example)

The PWM output of S3C2440 mainly uses the comparison register TCMPB0 (0x51000010).

When the timer is enabled, the timer count buffer register (TCNTBn) gets an initial value that is loaded into the down counter. The timer compare buffer register (TCMPBn) has an initial value that is loaded into the comparator for comparison with the down counter value.

Each timer has its own 16-bit down counter driven by the timer clock. When the down counter reaches zero, a timer interrupt request is generated to notify the CPU that the timer operation has been completed. When the timer counter reaches 0, the corresponding TCNTBn value is also loaded into the down counter to continue the next operation (auto-load). However, if the timer is stopped, for example by clearing the timer enable bit of TCONn in timer run mode, the value of TCNTBn is not loaded into the counter.

The value of TCMPBn is used for pulse width modulation. When the value of the down counter matches the value of the compare register in the timer control logic, the timer control logic changes the output level. Therefore, the compare register determines the on time of the PWM output.

With the above knowledge, we can know

When initializing the timer, the following registers need to be set (taking timer 0 as an example):

Timer output clock frequency = PCLK/(prescaler value + 1)/(divider value)

TCFG0 (0x51000000), such as: TCFG0 = 99; // prescaler value = "99"

TCFG1(0x51000004), such as: TCFG1=0x03;//divider value="1/16"

Thus, when PCLK=400M, the timer output frequency is 6.25M

Next, we need to set the initial value for the timer.

TCNTB0 (0x5100000c), for example, TCNTB0 = 62500; // load the initial value and interrupt once every 1s

TCMPB0 (0x51000010), for example, TCMPB0 = rTCNTB0>>1; // 50%

If PWM is not used, TCMPB0 can be left unset or set to 0.

Then you can start the timer, but you must manually load TCON=1<<1 for the first time;

After loading, change to automatic loading and start timer TCON=0x09;

Where TCON (0x51000008)

In order to drive the buzzer, the I/O port must be initialized.

The board I used was Friendly, and the buzzer was connected to GPB0.

Enable PWM by changing the last two bits of GPBCON (0x56000010)

void GPIO_init(void)

{

 rGPBCON &= ~3;

 rGPBCON |= 2;

}