238 lines
6.0 KiB
C
238 lines
6.0 KiB
C
/*
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* bmp180.c:
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* Extend wiringPi with the BMP180 I2C Pressure and Temperature
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* sensor. This is used in the Pi Weather Station
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* Copyright (c) 2016 Gordon Henderson
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*
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* Information from the document held at:
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* http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf
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* was very useful when building this code.
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*
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***********************************************************************
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* This file is part of wiringPi:
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* https://projects.drogon.net/raspberry-pi/wiringpi/
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*
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* wiringPi is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as
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* published by the Free Software Foundation, either version 3 of the
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* License, or (at your option) any later version.
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*
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* wiringPi is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with wiringPi.
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* If not, see <http://www.gnu.org/licenses/>.
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***********************************************************************
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*/
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#include <unistd.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <math.h>
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#include "wiringPi.h"
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#include "wiringPiI2C.h"
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#include "bmp180.h"
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#undef DEBUG
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#define I2C_ADDRESS 0x77
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#define BMP180_OSS 0
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// Static calibration data
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// The down-side of this is that there can only be one BMP180 in
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// a system - which is practice isn't an issue as it's I2C
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// address is fixed.
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static int16_t AC1, AC2, AC3 ;
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static uint16_t AC4, AC5, AC6 ;
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static int16_t VB1, VB2 ;
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static int16_t MB, MC, MD ;
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static double c5, c6, mc, md, x0, x1, x2, yy0, yy1, yy2, p0, p1, p2 ;
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// Pressure & Temp variables
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uint32_t cPress, cTemp ;
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static int altitude ;
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/*
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* read16:
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* Quick hack to read the 16-bit data with the correct endian
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*********************************************************************************
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*/
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uint16_t read16 (int fd, int reg)
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{
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return (wiringPiI2CReadReg8 (fd, reg) << 8) | wiringPiI2CReadReg8 (fd, reg + 1) ;
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}
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/*
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* bmp180ReadTempPress:
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* Does the hard work of reading the sensor
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*********************************************************************************
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*/
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static void bmp180ReadTempPress (int fd)
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{
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double fTemp, fPress ;
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double tu, a ;
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double pu, s, x, y, z ;
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uint8_t data [4] ;
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// Start a temperature sensor reading
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wiringPiI2CWriteReg8 (fd, 0xF4, 0x2E) ;
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delay (5) ;
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// Read the raw data
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data [0] = wiringPiI2CReadReg8 (fd, 0xF6) ;
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data [1] = wiringPiI2CReadReg8 (fd, 0xF7) ;
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// And calculate...
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tu = (data [0] * 256.0) + data [1] ;
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a = c5 * (tu - c6) ;
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fTemp = a + (mc / (a + md)) ;
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cTemp = (int)rint (((100.0 * fTemp) + 0.5) / 10.0) ;
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#ifdef DEBUG
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printf ("fTemp: %f, cTemp: %6d\n", fTemp, cTemp) ;
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#endif
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// Start a pressure snsor reading
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wiringPiI2CWriteReg8 (fd, 0xF4, 0x34 | (BMP180_OSS << 6)) ;
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delay (5) ;
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// Read the raw data
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data [0] = wiringPiI2CReadReg8 (fd, 0xF6) ;
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data [1] = wiringPiI2CReadReg8 (fd, 0xF7) ;
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data [2] = wiringPiI2CReadReg8 (fd, 0xF8) ;
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// And calculate...
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pu = ((double)data [0] * 256.0) + (double)data [1] + ((double)data [2] / 256.0) ;
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s = fTemp - 25.0 ;
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x = (x2 * pow (s, 2.0)) + (x1 * s) + x0 ;
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y = (yy2 * pow (s, 2.0)) + (yy1 * s) + yy0 ;
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z = (pu - x) / y ;
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fPress = (p2 * pow (z, 2.0)) + (p1 * z) + p0 ;
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cPress = (int)rint (((100.0 * fPress) + 0.5) / 10.0) ;
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#ifdef DEBUG
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printf ("fPress: %f, cPress: %6d\n", fPress, cPress) ;
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#endif
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}
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/*
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* myAnalogWrite:
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* Write to a fake register to represent the height above sea level
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* so that the peudo millibar register can read the pressure in mB
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*********************************************************************************
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*/
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static void myAnalogWrite (struct wiringPiNodeStruct *node, int pin, int value)
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{
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int chan = pin - node->pinBase ;
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if (chan == 0)
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altitude = value ;
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}
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/*
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* myAnalogRead:
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*********************************************************************************
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*/
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static int myAnalogRead (struct wiringPiNodeStruct *node, int pin)
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{
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int chan = pin - node->pinBase ;
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bmp180ReadTempPress (node->fd) ;
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/**/ if (chan == 0) // Read Temperature
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return cTemp ;
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else if (chan == 1) // Pressure
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return cPress ;
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else if (chan == 2) // Pressure in mB
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return cPress / pow (1 - ((double)altitude / 44330.0), 5.255) ;
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else
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return -9999 ;
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}
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/*
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* bmp180Setup:
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* Create a new instance of a PCF8591 I2C GPIO interface. We know it
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* has 4 pins, (4 analog inputs and 1 analog output which we'll shadow
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* input 0) so all we need to know here is the I2C address and the
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* user-defined pin base.
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*********************************************************************************
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*/
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int bmp180Setup (const int pinBase)
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{
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double c3, c4, b1 ;
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int fd ;
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struct wiringPiNodeStruct *node ;
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if ((fd = wiringPiI2CSetup (I2C_ADDRESS)) < 0)
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return FALSE ;
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node = wiringPiNewNode (pinBase, 4) ;
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node->fd = fd ;
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node->analogRead = myAnalogRead ;
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node->analogWrite = myAnalogWrite ;
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// Read calibration data
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AC1 = read16 (fd, 0xAA) ;
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AC2 = read16 (fd, 0xAC) ;
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AC3 = read16 (fd, 0xAE) ;
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AC4 = read16 (fd, 0xB0) ;
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AC5 = read16 (fd, 0xB2) ;
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AC6 = read16 (fd, 0xB4) ;
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VB1 = read16 (fd, 0xB6) ;
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VB2 = read16 (fd, 0xB8) ;
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MB = read16 (fd, 0xBA) ;
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MC = read16 (fd, 0xBC) ;
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MD = read16 (fd, 0xBE) ;
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// Calculate coefficients
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c3 = 160.0 * pow (2.0, -15.0) * AC3 ;
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c4 = pow (10.0, -3.0) * pow(2.0,-15.0) * AC4 ;
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b1 = pow (160.0, 2.0) * pow(2.0,-30.0) * VB1 ;
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c5 = (pow (2.0, -15.0) / 160.0) * AC5 ;
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c6 = AC6 ;
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mc = (pow (2.0, 11.0) / pow(160.0,2.0)) * MC ;
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md = MD / 160.0 ;
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x0 = AC1 ;
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x1 = 160.0 * pow (2.0, -13.0) * AC2 ;
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x2 = pow (160.0, 2.0) * pow(2.0,-25.0) * VB2 ;
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yy0 = c4 * pow (2.0, 15.0) ;
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yy1 = c4 * c3 ;
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yy2 = c4 * b1 ;
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p0 = (3791.0 - 8.0) / 1600.0 ;
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p1 = 1.0 - 7357.0 * pow (2.0, -20.0) ;
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p2 = 3038.0 * 100.0 * pow (2.0, -36.0) ;
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return TRUE ;
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}
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