7/23 Timers in Coldfire Processor Computer Science & Engineering Department Arizona State University Tempe, AZ Dr. Yann-Hang Lee (480)

set General Purpose Timer  The basic unit – counter (up or down)  a clock source  generate timing events (interrupts or timer output)  if overflow or reach 0  if match with a preset value  measure time – read counter values (captured)  free running, reset or reload, compare binary counter clock (external or internal) control circuit

set Measurement  Input-capture : identify the moment that an event occurs  latch the counter value when triggered  CPU can read the value later  Output compare : control the timing of output bit  CPU sets a value in output compare register  compare with counter every clock cycle  if equal, send an output signal  External event counting  Measuring elapsed time, pulse width, frequency, and period binary counter input capture register clock load interrupt or ready flag event edge detection

set Hardware Timer  Typical approach –  hardware unit generates an interrupt per unit of time (e.g. millisecond)  Avoid overflow with a software counter (in memory) – incremented when interrupts  assume the input clock of 2MHz (0.5x10 -3 ms)  set a compare counter to 1999  start counting with the input clock and, when equals to the compare register  interrupt  restart the counter from 0 binary counter = compare register (1999) input clock (2MHz) restart interrupt or toggle output

Delay Function using DMA Timer  Initialize a timer and input frequency  Set up a compare value  Check for flag or wait for interrupt set

DMA Timer  Control and status registers  mode register: #define MCF_DTIM3_DTMR *(vuint16*)(&__IPSBAR[0x0004C0]))  extended mode register  event register  reference register: for comparison  capture register: save counter value on capture event  counter register: counting set

Fucntion cpu_pause void cpu_pause_m(int usecs) { /* Enable the DMA Timer 3 */ MCF_DTIM3_DTRR = (usecs - 1); MCF_DTIM3_DTER = MCF_DTIM_DTER_REF;// 0x02 MCF_DTIM3_DTMR = 0 | MCF_DTIM_DTMR_PS(sys_clk_khz / 1000) | MCF_DTIM_DTMR_ORRI// 0x0010 | MCF_DTIM_DTMR_FRR// 0x0008 | MCF_DTIM_DTMR_CLK_DIV1// 0x0002 | MCF_DTIM_DTMR_RST;// 0x0001 while ((MCF_DTIM3_DTER & MCF_DTIM_DTER_REF) == 0) {}; /* Disable the timer */ MCF_DTIM3_DTMR = 0; } set

set Pulse Width Measurement  Capture counter values on edges  Read the difference to know the width  (count2-count1)/(timer frequency)  If the pulse is much longer, counter may overflow  interrupts on overflows  use software counter to count number of overflows. capture count1 capture count2

set Waveform Generator  Duty cycle : (pulse duration)/(clock period)  50% -- square wave  Free-running or reset on compare event  Use DMA timer to generate a square wave of 1KHz based on an input clock is 40MHz—  Pin assignment of DMA timer 0  Toggle output every 500  s  Mode register: CE, OM, ORPI, FRR, CLK, RST  Reference register: DTRR  500  s = 1/40MHz * (prescale+1) * (DTRR+1)

PWM in 5211  4 PWM outputs  8 channels  Counter (8 bits)  Period/duty  Even+odd channels  16 bit pwm  4 clock sources  A, SA, B, SB set

PWM in 5211  Initialization MCF_GPIO_PTAPAR = 0 | MCF_GPIO_PTAPAR_PTAPAR0(3); MCF_PWM_PWMPOL = 0 | MCF_PWM_PWMPOL_PPOL1; MCF_PWM_PWMCLK = 0|MCF_PWM_PWMCLK_PCLK1; MCF_PWM_PWMPRCLK = PRE_SCALE; MCF_PWM_PWMSCLA = SCALE; MCF_PWM_PWMPER1 = 255;  Set duty cycle MCF_PWM_PWMDTY(channel) = duty_cycle;  Enable pwm MCF_PWM_PWME = 0|MCF_PWM_PWME_PWME1 set