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129
basic-setup/components/u8g2/sys/arm/stm32l031x6/rtc_test/delay.c Normal file
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/*
delay.c
The delay function delay_micro_seconds() will use the global variable
SystemCoreClock. A call to SystemCoreClockUpdate() is required before
using delay_micro_seconds().
STM32L031 Project (U8g2 Library)
Copyright (c) 2017, olikraus@gmail.com
All rights reserved.
Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice, this list
of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice, this
list of conditions and the following disclaimer in the documentation and/or other
materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "stm32l031xx.h"
/* Generic ARM delay procedure, based on the system timer (SysTick) */
/*
Delay by the provided number of system ticks.
The delay must be smaller than the RELOAD value.
This delay has an imprecision of about +/- 20 system ticks.
*/
static void _delay_system_ticks_sub(uint32_t sys_ticks)
{
uint32_t start_val, end_val, curr_val;
uint32_t load;
start_val = SysTick->VAL;
start_val &= 0x0ffffffUL;
end_val = start_val;
if ( end_val < sys_ticks )
{
/* check, if the operation after this if clause would lead to a negative result */
/* if this would be the case, then add the reload value first */
load = SysTick->LOAD;
load &= 0x0ffffffUL;
end_val += load;
}
/* counter goes towards zero, so end_val is below start value */
end_val -= sys_ticks;
/* wait until interval is left */
if ( start_val >= end_val )
{
for(;;)
{
curr_val = SysTick->VAL;
curr_val &= 0x0ffffffUL;
if ( curr_val <= end_val )
break;
if ( curr_val > start_val )
break;
}
}
else
{
for(;;)
{
curr_val = SysTick->VAL;
curr_val &= 0x0ffffffUL;
if ( curr_val <= end_val && curr_val > start_val )
break;
}
}
}
/*
Delay by the provided number of system ticks.
Any values between 0 and 0x0ffffffff are allowed.
*/
void delay_system_ticks(uint32_t sys_ticks)
{
uint32_t load4;
load4 = SysTick->LOAD;
load4 &= 0x0ffffffUL;
load4 >>= 2;
while ( sys_ticks > load4 )
{
sys_ticks -= load4;
_delay_system_ticks_sub(load4);
}
_delay_system_ticks_sub(sys_ticks);
}
/*
Delay by the provided number of micro seconds.
Limitation: "us" * System-Freq in MHz must not overflow in 32 bit.
Values between 0 and 1.000.000 (1 second) are ok.
Important: Call SystemCoreClockUpdate() before calling this function.
*/
void delay_micro_seconds(uint32_t us)
{
uint32_t sys_ticks;
sys_ticks = SystemCoreClock;
sys_ticks /=1000000UL;
sys_ticks *= us;
delay_system_ticks(sys_ticks);
}