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Refs #789, #1874. Improved timer accuracy and added Modbus RTU support to the STM32F0 port. 

git-svn-id: https://svn.code.sf.net/p/openblt/code/trunk@1131 5dc33758-31d5-4daf-9ae8-b24bf3d40d73
This commit is contained in:
Frank Voorburg 2023-12-05 14:35:24 +00:00
parent 161d1422aa
commit 6463959ad7
2 changed files with 575 additions and 14 deletions
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503
Target/Source/ARMCM0_STM32F0/mbrtu.c Normal file
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@ -0,0 +1,503 @@
/************************************************************************************//**
* \file Source/ARMCM0_STM32F0/mbrtu.c
* \brief Bootloader Modbus RTU communication interface source file.
* \ingroup Target_ARMCM0_STM32F0
* \internal
*----------------------------------------------------------------------------------------
* C O P Y R I G H T
*----------------------------------------------------------------------------------------
* Copyright (c) 2023 by Feaser http://www.feaser.com All rights reserved
*
*----------------------------------------------------------------------------------------
* L I C E N S E
*----------------------------------------------------------------------------------------
* This file is part of OpenBLT. OpenBLT is free software: you can redistribute it and/or
* modify it under the terms of the GNU General Public License as published by the Free
* Software Foundation, either version 3 of the License, or (at your option) any later
* version.
*
* OpenBLT is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
* PURPOSE. See the GNU General Public License for more details.
*
* You have received a copy of the GNU General Public License along with OpenBLT. It
* should be located in ".\Doc\license.html". If not, contact Feaser to obtain a copy.
*
* \endinternal
****************************************************************************************/
/****************************************************************************************
* Include files
****************************************************************************************/
#include "boot.h" /* bootloader generic header */
#if (BOOT_COM_MBRTU_ENABLE > 0)
#include "stm32f0xx.h" /* STM32 CPU and HAL header */
#include "stm32f0xx_ll_usart.h" /* STM32 LL USART header */
/****************************************************************************************
* Macro definitions
****************************************************************************************/
/** \brief Timeout for transmitting a byte in milliseconds. */
#define MBRTU_BYTE_TX_TIMEOUT_MS (10u)
/* map the configured UART channel index to the STM32's USART peripheral */
#if (BOOT_COM_MBRTU_CHANNEL_INDEX == 0)
/** \brief Set UART base address to USART1. */
#define USART_CHANNEL USART1
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 1)
/** \brief Set UART base address to USART2. */
#define USART_CHANNEL USART2
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 2)
/** \brief Set UART base address to USART3. */
#define USART_CHANNEL USART3
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 3)
/** \brief Set UART base address to USART4. */
#define USART_CHANNEL USART4
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 4)
/** \brief Set UART base address to USART5. */
#define USART_CHANNEL USART5
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 5)
/** \brief Set UART base address to USART6. */
#define USART_CHANNEL USART6
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 6)
/** \brief Set UART base address to USART7. */
#define USART_CHANNEL USART7
#elif (BOOT_COM_MBRTU_CHANNEL_INDEX == 7)
/** \brief Set UART base address to USART8. */
#define USART_CHANNEL USART8
#endif
/****************************************************************************************
* Local data declarations
****************************************************************************************/
/** \brief Stores the number of free running counter ticks that represents the 3.5
* character delay time (T3_5) for Modbus RTU.
*/
static blt_int16u mbRtuT3_5Ticks;
/****************************************************************************************
* Function prototypes
****************************************************************************************/
static blt_bool MbRtuReceiveByte(blt_int8u *data);
static void MbRtuTransmitByte(blt_int8u data, blt_bool end_of_packet);
/************************************************************************************//**
** \brief Initializes the Modbus RTU communication interface.
** \attention It is the application's responsibility to initialize a timer peripheral
** to have an upwards counting free running counter, which runs at 100 kHz.
** \return none.
**
****************************************************************************************/
void MbRtuInit(void)
{
blt_int16u startTimeTicks;
blt_int16u deltaTimeTicks;
blt_int16u currentTimeTicks;
blt_int8u rxDummy;
LL_USART_InitTypeDef USART_InitStruct = {0};
/* the current implementation supports USART1 - USART8. throw an assertion error in
* case a different UART channel is configured.
*/
ASSERT_CT((BOOT_COM_MBRTU_CHANNEL_INDEX == 0) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 1) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 2) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 3) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 4) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 5) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 6) ||
(BOOT_COM_MBRTU_CHANNEL_INDEX == 7));
/* calculate the 3.5 character delay time in free running counter ticks. note that
* the free running counter runs at 100 kHz, so one tick is 10 us. For baudrates >
* 19200 bps, it can be fixed to 1750 us.
*/
if (BOOT_COM_MBRTU_BAUDRATE > 19200)
{
/* set T3_5 time to a fixed value of 1750 us. */
mbRtuT3_5Ticks = 175;
}
/* calculate the T3_5 time, because the baudrate is <= 19200 bps. */
else
{
/* T3_5 [us * 10] = 3.5 * Tchar = 3.5 * 11 * 100000 / baudrate = 3850000 / baudrate.
* make sure to do integer round up though. Make sure to add 1 to adjust for 10us
* timer resolution inaccuracy.
*/
mbRtuT3_5Ticks = (blt_int16u)(((3850000UL + (BOOT_COM_MBRTU_BAUDRATE - 1U)) /
BOOT_COM_MBRTU_BAUDRATE) + 1);
}
/* disable the UART peripheral */
LL_USART_Disable(USART_CHANNEL);
/* configure UART peripheral */
USART_InitStruct.BaudRate = BOOT_COM_MBRTU_BAUDRATE;
#if (BOOT_COM_MBRTU_STOPBITS == 1)
USART_InitStruct.StopBits = LL_USART_STOPBITS_1;
#else
USART_InitStruct.StopBits = LL_USART_STOPBITS_2;
#endif
#if (BOOT_COM_MBRTU_PARITY == 0)
USART_InitStruct.Parity = LL_USART_PARITY_NONE;
USART_InitStruct.DataWidth = LL_USART_DATAWIDTH_8B;
#elif (BOOT_COM_MBRTU_PARITY == 1)
USART_InitStruct.Parity = LL_USART_PARITY_ODD;
USART_InitStruct.DataWidth = LL_USART_DATAWIDTH_9B;
#else
USART_InitStruct.Parity = LL_USART_PARITY_EVEN;
USART_InitStruct.DataWidth = LL_USART_DATAWIDTH_9B;
#endif
USART_InitStruct.TransferDirection = LL_USART_DIRECTION_TX_RX;
USART_InitStruct.HardwareFlowControl = LL_USART_HWCONTROL_NONE;
USART_InitStruct.OverSampling = LL_USART_OVERSAMPLING_16;
/* initialize the UART peripheral */
LL_USART_Init(USART_CHANNEL, &USART_InitStruct);
LL_USART_Enable(USART_CHANNEL);
/* enable the receiver output to be able to receive. */
MbRtuDriverOutputControlHook(BLT_FALSE);
/* wait for idle line detection. This is T3_5 time after reception of the last byte. */
startTimeTicks = MbRtuFreeRunningCounterGet();
do
{
/* service the watchdog. */
CopService();
/* get the current value of the free running counter. */
currentTimeTicks = MbRtuFreeRunningCounterGet();
/* check if a byte was received while waiting for the idle line. */
if (MbRtuReceiveByte(&rxDummy) == BLT_TRUE)
{
/* restart the idle line detection. */
startTimeTicks = currentTimeTicks;
}
/* calculate the number of ticks that elapsed since the start or since the last
* byte reception. Note that this calculation works, even if the free running counter
* overflowed.
*/
deltaTimeTicks = currentTimeTicks - startTimeTicks;
}
while (deltaTimeTicks < mbRtuT3_5Ticks);
} /*** end of MbRtuInit ***/
/************************************************************************************//**
** \brief Transmits a packet formatted for the communication interface.
** \param data Pointer to byte array with data that it to be transmitted.
** \param len Number of bytes that are to be transmitted.
** \return none.
**
****************************************************************************************/
void MbRtuTransmitPacket(blt_int8u *data, blt_int8u len)
{
blt_int16u data_index;
blt_int16u checksum;
blt_bool endOfPacket = BLT_FALSE;
/* Made static to lower stack load and +5 for Modbus RTU packet overhead. */
static blt_int8u txPacket[BOOT_COM_MBRTU_TX_MAX_DATA + 5];
/* On Modbus RTU, there must always be a T3_5 time separation between packet trans-
* missions.
*
* This bootloader uses XCP packets embedded in Modbus RTU packets. The XCP
* communication is always request / response based. That means that this packet is
* a response packet and it will only be sent, after the reception of a request packet.
*
* A response packet is only deemed valid, after the T3_5 idle time. This module
* implements the T3_5 end-of-packet time event detection. Consequently, it is already
* guaranteed that there is T3_5 between subsequent packet transmissions. As such, no
* further T3_5 wait time is needed here.
*/
/* verify validity of the len-parameter */
ASSERT_RT(len <= BOOT_COM_MBRTU_TX_MAX_DATA);
/* construct the Modbus RTU packet. start by adding the slave address. */
txPacket[0] = BOOT_COM_MBRTU_NODE_ID;
/* add the user-defined function code for embedding XCP packets. */
txPacket[1] = BOOT_COM_MBRTU_FCT_CODE_USER_XCP;
/* add the XCP packet length. */
txPacket[2] = len;
/* copy the XCP packet data. */
CpuMemCopy((blt_int32u)&txPacket[3], (blt_int32u)data, len);
/* calculate the checksum for the packet, including slave address, function code and
* extra XCP length.
*/
checksum = MbRtuCrcCalculate(&txPacket[0], len + 3);
/* add the checksum at the end of the packet */
txPacket[len + 3] = (blt_int8u)(checksum & 0xff);
txPacket[len + 4] = (blt_int8u)(checksum >> 8);
/* enable the driver output to be able to send. just make sure to wait a little around
* the togglng of the DE/NRE pin.
*/
MbRtuDelay(BOOT_COM_MBRTU_DRIVER_OUTPUT_ENABLE_DELAY_US);
MbRtuDriverOutputControlHook(BLT_TRUE);
MbRtuDelay(BOOT_COM_MBRTU_DRIVER_OUTPUT_ENABLE_DELAY_US);
/* transmit all the packet bytes one-by-one */
for (data_index = 0; data_index < (len + 5); data_index++)
{
/* keep the watchdog happy */
CopService();
/* last byte of the packet? */
if (data_index == ((len + 5) - 1))
{
/* update the end of packet flag. */
endOfPacket = BLT_TRUE;
}
/* write byte */
MbRtuTransmitByte(txPacket[data_index], endOfPacket);
}
/* enable the receiver output to be able to receive again. just make sure to wait a
* little around the togglng of the DE/NRE pin.
*/
MbRtuDelay(BOOT_COM_MBRTU_DRIVER_OUTPUT_DISABLE_DELAY_US);
MbRtuDriverOutputControlHook(BLT_FALSE);
MbRtuDelay(BOOT_COM_MBRTU_DRIVER_OUTPUT_DISABLE_DELAY_US);
} /*** end of MbRtuTransmitPacket ***/
/************************************************************************************//**
** \brief Receives a communication interface packet if one is present.
** \param data Pointer to byte array where the data is to be stored.
** \param len Pointer where the length of the packet is to be stored.
** \return BLT_TRUE if a packet was received, BLT_FALSE otherwise.
**
****************************************************************************************/
blt_bool MbRtuReceivePacket(blt_int8u *data, blt_int8u *len)
{
blt_bool result = BLT_FALSE;
blt_int8u rxByte;
blt_int16u currentTimeTicks;
blt_int16u deltaTimeTicks;
blt_int16u checksumCalculated;
blt_int16u checksumReceived;
/* Made static to lower stack load and +5 for Modbus RTU packet overhead. */
static blt_int8u rxPacket[BOOT_COM_MBRTU_RX_MAX_DATA + 5];
static blt_int8u rxLength = 0;
static blt_bool packetRxInProgress = BLT_FALSE;
static blt_int16u lastRxByteTimeTicks = 0;
/* get the current value of the free running counter. */
currentTimeTicks = MbRtuFreeRunningCounterGet();
/* check for a newly received byte. */
if (MbRtuReceiveByte(&rxByte) == BLT_TRUE)
{
/* store the time at which the byte was received. */
lastRxByteTimeTicks = currentTimeTicks;
/* is this the potential start of a new packet? */
if (packetRxInProgress == BLT_FALSE)
{
/* initialize the reception of a new packet. */
rxLength = 0;
packetRxInProgress = BLT_TRUE;
}
/* store the newly received byte in the buffer, with buffer overrun protection. */
if (rxLength < (sizeof(rxPacket)/sizeof(rxPacket[0])))
{
rxPacket[rxLength] = rxByte;
rxLength++;
}
/* buffer overrun occurred. received packet was longer than supported so discard
* the packet to try and sync to the next one.
*/
else
{
/* discard the partially received packet. */
packetRxInProgress = BLT_FALSE;
}
}
/* only attempt to detect the end of packet, when a reception is in progress. */
if (packetRxInProgress == BLT_TRUE)
{
/* calculate the number of ticks that elapsed since the last byte reception. note
* that this calculation works, even if the free running counter overflowed.
*/
deltaTimeTicks = currentTimeTicks - lastRxByteTimeTicks;
/* packet reception is assumed complete after T3_5 of not receiving new data. */
if (deltaTimeTicks >= mbRtuT3_5Ticks)
{
/* a Modbus RTU packet consists of at least the address field, function code and
* 16-bit CRC. Validate the packet length based on this info.
*/
if (rxLength >= 4)
{
/* calculate the packet checksum. */
checksumCalculated = MbRtuCrcCalculate(&rxPacket[0], rxLength - 2);
/* extract the checksum received with the packet. */
checksumReceived = rxPacket[rxLength - 2] | (rxPacket[rxLength - 1] << 8);
/* only continue with packet processing if the checksums match. */
if (checksumCalculated == checksumReceived)
{
/* we are only interested in Modbus RTU packets that are addressed to us and
* have an XCP packet embedded.
*/
if ( (rxPacket[0] == BOOT_COM_MBRTU_NODE_ID) &&
(rxPacket[1] == BOOT_COM_MBRTU_FCT_CODE_USER_XCP) )
{
/* An XCP packet embedded in a Modbus RTU packet has an extra XCP packet
* length value. Use it to double-check that the packet length is valid.
*/
if (rxPacket[2] == (rxLength - 5))
{
/* copy the packet's XCP data. */
CpuMemCopy((blt_int32u)data, (blt_int32u)&rxPacket[3], rxLength - 5);
/* set the packet's XCP length. */
*len = rxLength - 5;
/* update the result to success to indicate that this XCP packet is ready
* for processing.
*/
result = BLT_TRUE;
}
}
}
}
/* reset the packet reception in progress flag, to be able to receive the next. */
packetRxInProgress = BLT_FALSE;
}
}
/* give the result back to the caller. */
return result;
} /*** end of MbRtuReceivePacket ***/
/************************************************************************************//**
** \brief Receives a communication interface byte if one is present.
** \param data Pointer to byte where the data is to be stored.
** \return BLT_TRUE if a byte was received, BLT_FALSE otherwise.
**
****************************************************************************************/
static blt_bool MbRtuReceiveByte(blt_int8u *data)
{
blt_bool result = BLT_FALSE;
/* check if a new byte was received on the configured channel */
if (LL_USART_IsActiveFlag_RXNE(USART_CHANNEL) != 0)
{
/* update the result */
result = BLT_TRUE;
/* check for a frame error. the frame error check is important because it can detect
* a missing stopbit. on an RS485 bus without bias resistors, the A-B differential
* voltage is 0. for an RS485 transceiver this is neither a 0 nor a 1 bit, so
* undefined. most RS485 transceivers feature a reception failsafe function to drive
* the Rx output (going to the UART Rx) to a defined state of logic 1. in case the
* used RS485 transceiver doesn't have such a feature, it typically leaves the Rx
* output in a logic 0 state. this means that after the stop bit of the last packet
* byte, the UART Rx input sees a logic 0, and assumes it is a start bit. the
* remaining data bits will always be 0 and, most importantly no stop bit is
* present, causing a framing error. Long story short: if you don't check for the
* framing error flag, you might receive an extra byte with value 0, which is not
* actually transmitted on the RS485 bus. you can catch and ignore this byte by doing
* a frame error check.
*/
if (LL_USART_IsActiveFlag_FE(USART_CHANNEL) != 0)
{
/* clear the error flag. */
LL_USART_ClearFlag_FE(USART_CHANNEL);
/* ignore the byte because of a detected frame error. */
result = BLT_FALSE;
}
#if (BOOT_COM_MBRTU_PARITY > 0)
/* check for a parity error. */
if (LL_USART_IsActiveFlag_PE(USART_CHANNEL) != 0)
{
/* clear the error flag. */
LL_USART_ClearFlag_PE(USART_CHANNEL);
/* ignore the byte because of a detected parity error. */
result = BLT_FALSE;
}
#endif
/* retrieve and store the newly received byte */
*data = LL_USART_ReceiveData8(USART_CHANNEL);
}
/* give the result back to the caller */
return result;
} /*** end of MbRtuReceiveByte ***/
/************************************************************************************//**
** \brief Transmits a communication interface byte.
** \param data Value of byte that is to be transmitted.
** \param end_of_packet BLT_TRUE if this is the last byte of the packet, BLT_FALSE
** otherwise.
** \return none.
**
****************************************************************************************/
static void MbRtuTransmitByte(blt_int8u data, blt_bool end_of_packet)
{
blt_int32u timeout;
/* write byte to transmit holding register */
LL_USART_TransmitData8(USART_CHANNEL, data);
/* set timeout time to wait for transmit completion. */
timeout = TimerGet() + MBRTU_BYTE_TX_TIMEOUT_MS;
/* not the last byte of the packet? */
if (end_of_packet == BLT_FALSE)
{
/* wait for tx holding register to be empty */
while (LL_USART_IsActiveFlag_TXE(USART_CHANNEL) == 0)
{
/* keep the watchdog happy */
CopService();
/* break loop upon timeout. this would indicate a hardware failure. */
if (TimerGet() > timeout)
{
break;
}
}
}
/* this is the last byte of a packet. */
else
{
/* wait for tx complete event. this is needed for the last byte, otherwise the
* transceiver's transmit output gets disabled with MbRtuDriverOutputControlHook()
* before the byte reception completes.
*/
while (LL_USART_IsActiveFlag_TC(USART_CHANNEL) == 0)
{
/* keep the watchdog happy */
CopService();
/* break loop upon timeout. this would indicate a hardware failure. */
if (TimerGet() > timeout)
{
break;
}
}
}
} /*** end of MbRtuTransmitByte ***/
/************************************************************************************//**
** \brief Obtains the counter value of the 100 kHz free running counter. Note that
** each count represent 10 us. The Modbus RTU communication module uses this
** free running counter for Modbus RTU packet timing related purposes. The
** already available 1 ms timer does not have the needed resolution for this
** purpose.
** \return Current value of the free running counter.
**
****************************************************************************************/
blt_int16u MbRtuFreeRunningCounterGet(void)
{
blt_int16u result;
/* This port's timer module is based on a 100 kHz free running counter, which is
* already configured and running. Therefore we just need to read out its free running
* counter value.
*/
result = (blt_int16u)TIM1->CNT;
/* give the result back to the caller. */
return result;
} /*** end of MbRtuFreeRunningCounterGet ***/
#endif /* BOOT_COM_MBRTU_ENABLE > 0 */
/*********************************** end of mbrtu.c ************************************/

86
Target/Source/ARMCM0_STM32F0/timer.c
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@ -31,6 +31,20 @@
****************************************************************************************/
#include "boot.h" /* bootloader generic header */
#include "stm32f0xx.h" /* STM32 CPU and HAL header */
#include "stm32f0xx_ll_bus.h" /* STM32 LL BUS header */
#include "stm32f0xx_ll_rcc.h" /* STM32 LL RCC header */
/****************************************************************************************
* Macro definitions
****************************************************************************************/
/** \brief Frequency of the configured timer peripheral's free running counter in Hz.
* This shoud be 100 kHz.
*/
#define TIMER_COUNTER_FREQ_HZ (100000U)
/** \brief Number of free running counter counts that equal one millisecond. */
#define TIMER_COUNTS_PER_MS (TIMER_COUNTER_FREQ_HZ / 1000U)
/****************************************************************************************
@ -41,6 +55,9 @@
*/
static blt_int32u millisecond_counter;
/** \brief Buffer for storing the last value of the free running counter. */
static blt_int16u free_running_counter_last;
/************************************************************************************//**
** \brief Initializes the polling based millisecond timer driver.
@ -49,16 +66,35 @@ static blt_int32u millisecond_counter;
****************************************************************************************/
void TimerInit(void)
{
/* reset the timer configuration */
TimerReset();
/* configure the systick frequency as a 1 ms event generator */
SysTick->LOAD = BOOT_CPU_SYSTEM_SPEED_KHZ - 1;
/* reset the current counter value */
SysTick->VAL = 0;
/* select core clock as source and enable the timer */
SysTick->CTRL = SysTick_CTRL_CLKSOURCE_Msk | SysTick_CTRL_ENABLE_Msk;
/* reset the millisecond counter value */
blt_int8u tim_multiplier;
blt_int32u pclk1_frequency;
blt_int32u pclk1_tim_frequency;
/* All STM32F0 derivatives support a TIM1 peripheral. Its free running counter will be
* used to realize the polling based millisecond time reference in this module.
* Start by enabling the periperhal.
*/
LL_APB1_GRP2_EnableClock(LL_APB1_GRP2_PERIPH_TIM1);
/* The TIM1 peripheral clock is derived from PCLK1. Obtain the PCLK1 frequency. */
pclk1_frequency = __LL_RCC_CALC_PCLK1_FREQ(SystemCoreClock, LL_RCC_GetAPB1Prescaler());
/* According to the clock tree diagram in the RCC chapter of the reference manual,
* the PCLK1-TIM frequency = PLCK1 * 1, when the APB1 prescaler is 1, otherwise it is
* PCLK1 * 2.
*/
tim_multiplier = (LL_RCC_GetAPB1Prescaler() == LL_RCC_APB1_DIV_1) ? 1U : 2U;
/* Obtain the PCLK2-TIM frequency. */
pclk1_tim_frequency = pclk1_frequency * tim_multiplier;
/* Configure the free running counter as a 16-bit upwards counter that runs at the
* desired frequency and enable it.
*/
TIM1->CR1 = TIM_CR1_CEN;
TIM1->ARR = 65535U;
TIM1->PSC = (pclk1_tim_frequency / TIMER_COUNTER_FREQ_HZ) - 1U;
/* Generate an update event to reload the prescaler immediately. */
TIM1->EGR |= TIM_EGR_UG;
/* Initialize locals. */
millisecond_counter = 0;
free_running_counter_last = (blt_int16u)TIM1->CNT;
} /*** end of TimerInit ***/
@ -70,7 +106,13 @@ void TimerInit(void)
****************************************************************************************/
void TimerReset(void)
{
/* set the systick's registers back into the default reset value. */
/* Bring the TIM1 peripheral back into its reset state and disable its clock. */
LL_APB1_GRP2_ForceReset(LL_APB1_GRP2_PERIPH_TIM1);
LL_APB1_GRP2_ReleaseReset(LL_APB1_GRP2_PERIPH_TIM1);
LL_APB1_GRP2_DisableClock(LL_APB1_GRP2_PERIPH_TIM1);
/* Set the SysTick's registers back into the default reset value. Note that this module
* does not use the SysTick, but HAL_Init() did initialize it.
*/
SysTick->CTRL = 0;
SysTick->LOAD = 0;
SysTick->VAL = 0;
@ -84,11 +126,27 @@ void TimerReset(void)
****************************************************************************************/
void TimerUpdate(void)
{
/* check if the millisecond event occurred */
if ((SysTick->CTRL & SysTick_CTRL_COUNTFLAG_Msk) != 0)
blt_int16u free_running_counter_now;
blt_int16u delta_counts;
blt_int16u ms_counts;
/* Get the current value of the free running counter. */
free_running_counter_now = (blt_int16u)TIM1->CNT;
/* Calculate the number of counts that passed since the detection of the last
* millisecond event. Note that this calculation also works, in case the free running
* counter overflowed, thanks to integer math.
*/
delta_counts = free_running_counter_now - free_running_counter_last;
/* Did one or more milliseconds pass since the last event? */
if (delta_counts >= TIMER_COUNTS_PER_MS)
{
/* increment the millisecond counter */
millisecond_counter++;
/* Calculate how many milliseconds passed. */
ms_counts = delta_counts / TIMER_COUNTS_PER_MS;
/* Update the millisecond counter. */
millisecond_counter += ms_counts;
/* Store the counter value of the last millisecond event, to detect the next one. */
free_running_counter_last += (ms_counts * TIMER_COUNTS_PER_MS);
}
} /*** end of TimerUpdate ***/