s3c2440 experiment---timer

　A clock is a synchronized beat that synchronizes a working system.

　1. There are many ways to obtain a clock

　　1. External direct input clock signal

　　2. External crystal oscillator + internal clock generator (low-frequency microcontroller)

　　3. External crystal oscillator + internal clock generator + PLL + internal frequency divider

  2. Internal structure of timer

　　1. Total clock system

　　　　Detailed description: When the 2440 is just turned on, since the PLL has not yet been turned on, FCLK is equal to the external input clock (12MHz). If you want to provide the clock frequency, you must turn on the PLL. PLL is divided into

MPLL and UPLL. Among them, UPLL controls USB, which has nothing to do with this experiment. MPLL is divided into three types of clocks: FCLK (CPU core clock), HCLK (AHB bus device clock), and PCLK (APK bus device clock).

　　2. Experiment content: Use timer 0 to make the LED light flash at a fixed time

　　As shown in the figure above: the route for timer 0 to obtain the clock frequency is: PCLK->prescaler->divider->MUX circuit->control logic unit->timer 0

3. Analysis before experiment

　　Through the above route, we can know that we need to carry out the following steps:

　　1. Obtain the PCLK clock (since PCLK is separated from MPLL, we need to set the value of MPLL first, and then set the PCLK through frequency division (register CLKDIV))

　　2. Set the prescaler (TCFG0)

　　3. Set the frequency divider (TCFG1)

　　4. Set MUX circuit (default)

　　5. Set the control unit (TCNTB0)

　　When using the timer for the first time, you need to set the "manual update" bit to 1 so that the value of the TCNTB0 register is loaded into TCNT0. The number can then be automatically loaded into the register via auto-reload.

4. Core code analysis

　　1. Initialize the clock　　

　　　　void init_timer(void)
　　　　{
　　　　　　//Step one: configure FCLK:HCLK:PCLK
　　　　　　CLKDIVN = 0x03;

　　　　　　/* If HDIVN is non-0, the CPU bus mode should change from "fast bus mode" to "asynchronous bus mode" */
　　　　　　__asm__(
　　　　　　"mrc p15, 0, r1, c1, c0, 0n" /* Read the control register* /
　　　　　　"orr r1, r1, #0xc0000000n" /* Set to "asynchronous bus mode" */
　　　　　　"mcr p15, 0, r1, c1, c0, 0n" /* Write to the control register */
　　　　　　);

　　　　　　//Step 2 : Configure MPLL
　　　　　　MPLLCON = FCLK; //200MHz


　　　　　　//Step 3: Set timer 0. At this time, PCLK is 50MHz
　　　　　　TCFG0 = 99; //Prescaler
　　　　　　TCFG1 = 0x03; //Frequency divider
　　　　　　TCNTB0 = 31250; // Timing time
　　　　　　TCON |= (1<<1);
　　　　　　TCON = 0x09;

　　　　　　//Enable timer 0

　　　　　　INTMSK &= (~(1<<10));
　　　　}

　　2. An interrupt occurs when the timer expires

　　　　void irq_timer(void)
　　　　{
　　
　　　　　　if(INTOFFSET == 10)
　　　　　　{
　　　　　　　　GPFDAT &= (~(1<<4));

　　　　　　}


　　　　　SRCPND = (1<　　　　　INTPND = INTPND;

　　　　　　}

5. Summary

　　In the timer, the clock configuration of timer 0 is the focus. From PLL to timer 0, there is a lot that needs to be configured in the middle. Especially when setting the reload value for the first time, you need to update it manually. By writing a blog, I have deepened my understanding of the s3c2440 timer. I will insist on continuing to write. ☀