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adc.c
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118 lines (94 loc) · 3.58 KB
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/**************************************************************************/
/*!
@file adc.c
@author ChrisMicro
@author unknown others
@brief ADC functions, LPC810 has no ADC therefore other tricks are used
@section LICENSE see below for my code contribution
*/
/**************************************************************************/
#include "LPC8xx.h"
#include "adc.h"
#include "mrt.h"
uint16_t read_adc2();
// tbd: channel selection
void init_adc(uint8_t channel)
{
// Enable AHB clock to the ACMP
LPC_SYSCON->SYSAHBCLKCTRL |= (1 << 19);
// Enable fixed function ACMP_I2. This function is connected on pin PIO0_1
LPC_SWM->PINENABLE0 &= (~0x2);
// Initialize the comparator ICMP_2
LPC_SYSCON->PDRUNCFG &= ~((1 << 15)); // power up ACMP
}
uint16_t read_adc(uint8_t channel)
{
return read_adc2(); // tbd: other channels
}
/*
*
* Use ACMP_2 as a simple 5 bit SAR adc
*
* copied from:
* http://blog.nano-age.co.uk/2014/08/creating-5-bit-successive-approximation.html
*
* LICENSE: unclear
*
* */
uint16_t read_adc2()
{
int min = 0, max = 63, value = 31, count, compstat, laststat;
LPC_CMP->CTRL = (0x2 << 8) | (0x3 << 25); /* positive input ACMP0_I2 , negative input voltage ladder , 20mV hysteresis */
while (!((value == min) || (value == max)))
{
count = 0;
LPC_CMP->LAD = 1 | (value); /* ladder Enable | Vref=Vdd | value */
delayMicroseconds(15); // 15us worst case for ladder to settle
laststat = (LPC_CMP->CTRL >> 21) & 1;
// wait till reading is the same 3 times in row
do
{
delayMicroseconds(1); // minimum wait time: 0.5us
compstat = (LPC_CMP->CTRL >> 21) & 1;
if (compstat == laststat)
count++;
else
count = 0;
laststat = compstat;
} while (count < 3);
// Binary divide
if (compstat)
{
min = value;
value = value + ((max - value) >> 1);
} else
{
max = value;
value = value - ((value - min) >> 1);
}
}
return value >> 1;
}
/***********************************************************************************
Software License Agreement (BSD License)
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. 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.
3. Neither the name of the copyright holders nor the
names of its contributors may be used to endorse or promote products
derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS ''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 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.
***********************************************************************************/