yefj
Advanced Member level 5
Hello ,I am using an example code shown bellow, which defines the timer as shown in the refrence guide link bellow.
from teh example code shown bellow the upper limit of the counter is set by TIMER_TopBufSet(TIMER0, (hfperFreq / (2 * OUTPUT_FREQ_Hz)));
if our clock is 10Mhz and we want our outputclock to be 1Mhz then we need to count from one to 10 each tick of 10Mhz clock and change value when we reach 10.
why is 2*output_freq in the code?
Thanks.
page 691:
from teh example code shown bellow the upper limit of the counter is set by TIMER_TopBufSet(TIMER0, (hfperFreq / (2 * OUTPUT_FREQ_Hz)));
if our clock is 10Mhz and we want our outputclock to be 1Mhz then we need to count from one to 10 each tick of 10Mhz clock and change value when we reach 10.
why is 2*output_freq in the code?
Thanks.
page 691:
Code:
/***************************************************************************//**
* @file main_gpio_slew_rate.c
* @brief Demonstrates the slew rate settings for the GPIO. A 1 MHz square wave
* is generated on a pin. The slew rate setting is changed by pressing PB0. The
* drive strength setting is changed by pressing PB1. The effects of these
* settings on the pin's slew rate can be observed by placing a 50uF capacitor
* on the output pin and observing the change in rise and fall times of the 1
* MHz square wave.
*******************************************************************************
* # License
* <b>Copyright 2020 Silicon Laboratories Inc. www.silabs.com</b>
*******************************************************************************
*
* SPDX-License-Identifier: Zlib
*
* The licensor of this software is Silicon Laboratories Inc.
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
*
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
*
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*
*******************************************************************************
* # Evaluation Quality
* This code has been minimally tested to ensure that it builds and is suitable
* as a demonstration for evaluation purposes only. This code will be maintained
* at the sole discretion of Silicon Labs.
******************************************************************************/
#include "em_device.h"
#include "em_chip.h"
#include "em_cmu.h"
#include "em_gpio.h"
#include "em_timer.h"
#include "em_emu.h"
#include "bsp.h"
#include "stdio.h"
#if defined(BSP_STK_BRD2204A) || defined(BSP_STK_BRD2102A) /* GG11 or TG11 STK square wave on PD1 */
#define SQUARE_WAVE_PORT gpioPortD
#define SQUARE_WAVE_PIN 1
#define SQUARE_WAVE_LOC TIMER_ROUTELOC0_CC0LOC_LOC2
#else /* All other STKs, square wave on PA0 */
#define SQUARE_WAVE_PORT gpioPortA
#define SQUARE_WAVE_PIN 0
#define SQUARE_WAVE_LOC TIMER_ROUTELOC0_CC0LOC_LOC0
#endif
/**************************************************************************//**
* @brief Setup GPIO interrupt for pushbuttons and PA0 output.
*****************************************************************************/
static void gpioSetup(void)
{
// Enable GPIO clock.
CMU_ClockEnable(cmuClock_GPIO, true);
// Configure PB0 as input and enable interrupt.
GPIO_PinModeSet(BSP_GPIO_PB0_PORT, BSP_GPIO_PB0_PIN, gpioModeInputPull, 1);
GPIO_ExtIntConfig(BSP_GPIO_PB0_PORT, BSP_GPIO_PB0_PIN, BSP_GPIO_PB0_PIN, false, true, true);
// Configure PB1 as input and enable interrupt.
GPIO_PinModeSet(BSP_GPIO_PB1_PORT, BSP_GPIO_PB1_PIN, gpioModeInputPull, 1);
GPIO_ExtIntConfig(BSP_GPIO_PB1_PORT, BSP_GPIO_PB1_PIN, BSP_GPIO_PB1_PIN, false, true, true);
NVIC_ClearPendingIRQ(GPIO_EVEN_IRQn);
NVIC_EnableIRQ(GPIO_EVEN_IRQn);
NVIC_ClearPendingIRQ(GPIO_ODD_IRQn);
NVIC_EnableIRQ(GPIO_ODD_IRQn);
// Set PA0 to push-pull output
CMU_ClockEnable(cmuClock_GPIO, true);
GPIO_PinModeSet(SQUARE_WAVE_PORT, SQUARE_WAVE_PIN, gpioModePushPull, 1);
}
GPIO_DriveStrength_TypeDef driveStrength = gpioDriveStrengthStrongAlternateStrong;
uint32_t slewRate = 6;
/**************************************************************************//**
* @brief Unified GPIO Interrupt handler (pushbuttons).
* PB0 Cycles through slew rate settings.
* PB1 Cycles through drive strength settings.
*****************************************************************************/
void GPIO_Unified_IRQ(void)
{
// Get and clear all pending GPIO interrupts.
uint32_t interruptMask = GPIO_IntGet();
GPIO_IntClear(interruptMask);
// Act on interrupts.
if (interruptMask & (1 << BSP_GPIO_PB0_PIN))
{
// BTN0: Slew Rate
slewRate += 1;
if (slewRate > 7)
{
slewRate = 0;
}
}
if (interruptMask & (1 << BSP_GPIO_PB1_PIN))
{
// BTN1: cycle through drive strength settings.
if (driveStrength == gpioDriveStrengthStrongAlternateStrong)
{
driveStrength = gpioDriveStrengthWeakAlternateWeak;
}
else
{
driveStrength = gpioDriveStrengthStrongAlternateStrong;
}
}
}
/**************************************************************************//**
* @brief GPIO Interrupt handler for even pins.
*****************************************************************************/
void GPIO_EVEN_IRQHandler(void)
{
GPIO_Unified_IRQ();
}
/**************************************************************************//**
* @brief GPIO Interrupt handler for odd pins.
*****************************************************************************/
void GPIO_ODD_IRQHandler(void)
{
GPIO_Unified_IRQ();
}
#define OUTPUT_FREQ_Hz (1000000UL)
/**************************************************************************//**
* @brief Timer setup to output a square wave on PA0
*****************************************************************************/
void timerSetup(void)
{
// Set Timer0 to toggle PA0 at 1 MHz
CMU_ClockEnable(cmuClock_TIMER0, true);
uint32_t hfperFreq = CMU_ClockFreqGet(cmuClock_HFPER);
TIMER_TopBufSet(TIMER0, (hfperFreq / (2 * OUTPUT_FREQ_Hz)));
TIMER_Init_TypeDef init = TIMER_INIT_DEFAULT;
TIMER_Init(TIMER0, &init);
TIMER_InitCC_TypeDef initCh = TIMER_INITCC_DEFAULT;
initCh.cofoa = timerOutputActionToggle;
initCh.mode = timerCCModeCompare;
TIMER_InitCC(TIMER0, 0, &initCh);
TIMER0->ROUTEPEN |= TIMER_ROUTEPEN_CC0PEN;
TIMER0->ROUTELOC0 |= SQUARE_WAVE_LOC;
}
/**************************************************************************//**
* @brief Main function
*
* This example demonstrates the slew rate settings for the GPIO. A 1 MHz
* square wave is generated on a pin. The slew rate setting is changed by
* pressing BTN0. The drive strength setting is changed by pressing BTN1. The
* effects of these settings on the pin's slew rate can be observed by placing
* a 50 pF capacitor on the output pin and observing the change in rise and
* fall times of the 1 MHz square wave.
*
* Output pin is PD1 on SLSTK3701 (EFM32GG11 STK) and SLSTK3301 (EFM32TG11 STK)
* and PA0 on other kits.
*
* To test:
* 1. Place a 50 pF capacitor between the square wave output and GND.
* 2. Upload and run the example.
* 3. While observing the rise and fall times of the waveform on PA0/PD1:
* a. Press BTN0 to change the slew rate setting
* b. Press BTN1 to change the drive strength setting
*****************************************************************************/
int main(void)
{
/* Chip errata */
CHIP_Init();
/* Initialize Push Buttons and PA0 */
gpioSetup();
/* Initialize PA0 square-wave output */
timerSetup();
/* Infinite loop */
while (1)
{
/* Update PA0 drive strength and slew rate */
GPIO_DriveStrengthSet(SQUARE_WAVE_PORT, driveStrength);
GPIO_SlewrateSet(SQUARE_WAVE_PORT, slewRate, slewRate);
/* Enter EM1 until a push-button interrupt triggers a wake-up */
EMU_EnterEM1();
}
}
