prelab 5 University of Michigan EECS 461

EECS 461
Prelab 5
Due 02/18/2020

1.
T_clock = 1/40e6 = 2.5e-8 s

For 20 kHz,
T_interrupt = 1/20e3 s = 5e-5s
⇒ ​# LPIT clocks​ = 5e-5/2.5e-8 = ​2000
⇒ timer initial value (TMR_VAL) = 2000 - 1 = ​1999

For 1 kHz,
T_interrupt = 1/1e3 kHz = 1e-3s
⇒ ​# LPIT clocks​ = 1e-3/2.5e-8 = ​40000
⇒ timer initial value (TMR_VAL) = 40000- 1 = ​39999

/*
LPIT.h
University of Michigan
EECS 461, Embedded Control Systems
Low Power Interrupt Timer (LPIT)
Read Chapter 30 in S32K144 User's Manual

Revision History:
2017-11-16 schmo
2017-03-13 Paul Domanico
*/

#include "LPIT.h"

/* Array of 4 interrupt service routines. One for each channel */
static int LPIT_IRQn[4] = LPIT_IRQS;/* fill in */

void enableLPIT(){
/* 29.6.5 PCC LPIT Register */
PCC->PCCn[PCC_LPIT_INDEX] = PCC_PCCn_CGC(0b0); /* fill in */; /* Disable PCC
LPIT clock to change PCS */
PCC->PCCn[PCC_LPIT_INDEX] = PCC_PCCn_PCS(110); /* fill in */; /* Clock
source: SPLL2_DIV2_CLK */
PCC->PCCn[PCC_LPIT_INDEX] = PCC_PCCn_CGC(0b1); /* fill in */; /* Enable
clk to LPIT0 regs */

/* 46.4.1.4.2 Module Control Register */

, LPIT0->MCR = LPIT_MCR_M_CEN(0b1)/* fill in */; /* enable module clk
(allows writing other LPIT0 regs)*/
}



void initLPIT(const uint8_t channel, const uint32_t frequency, const isr_t
handler, const uint32_t priority) {
/* 46.4.1.9.3 Timer Value Register */
LPIT0->TMR[channel].TVAL = TMR_VAL/* fill in */; /* channel timer start
value */

/* 46.4.1.6.2 Module Interrupt Enable Register */
LPIT0->MIER = 1 << channel; /* fill in */; /* Timer Interrupt Enabled for
Channel */

/* 46.4.1.9.3 Timer Control Register */
LPIT0->TMR[channel].TCTRL = /* fill in */; /* T_EN : Timer channel is
disabled to set registers*/
LPIT0->TMR[channel].TCTRL = LPIT_TMR_TCTRL_MODE(0)/* fill in */; /* MODE :
32 periodic counter mode */
LPIT0->TMR[channel].TCTRL = LPIT_TMR_TCTRL_TSOT(0)/* fill in */; /* TSOT :
Timer decrements immediately based on restart */
LPIT0->TMR[channel].TCTRL = LPIT_TMR_TCTRL_TSOI(0)/* fill in */; /* TSOI :
Timer does not stop after timeout */
LPIT0->TMR[channel].TCTRL = LPIT_TMR_TCTRL_TROT(0)/* fill in */; /* TROT :
ignore external trigger */

/* 46.4.1.7.3 Set Timer Enable Register */
LPIT0->SETTEN = 1 << channel/* fill in */; /*SET_T_EN_n : enable timer
for channel */

/* defined in interrupt_manager.c */
INT_SYS_InstallHandler(LPIT_IRQn[channel], handler, (isr_t*) 0);
INT_SYS_SetPriority(LPIT_IRQn[channel], priority);
INT_SYS_EnableIRQ(LPIT_IRQn[channel]);
}



void clearFlagLPIT(const uint8_t channel){
/* 46.4.1.5.3 Module Status Register */
LPIT0->MSR = 1 << channel;/* fill in */; /* clear TIFn */
}