i2c.cpp

00001 /**
00002  * Copyright (c) 2010 Roy van Dam <roy@negative-black.org>
00003  * All rights reserved.
00004  *
00005  * Redistribution and use in source and binary forms, with or without
00006  * modification, are permitted provided that the following conditions
00007  * are met:
00008  * 1. Redistributions of source code must retain the above copyright
00009  *    notice, this list of conditions and the following disclaimer.
00010  * 2. Redistributions in binary form must reproduce the above copyright
00011  *    notice, this list of conditions and the following disclaimer in the
00012  *    documentation and/or other materials provided with the distribution.
00013  *
00014  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
00015  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00016  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00017  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
00018  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00019  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
00020  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
00021  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00022  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
00023  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
00024  * SUCH DAMAGE.
00025  */
00026 
00027 #include "i2c.hpp"
00028 
00029 namespace SHTx {
00030     I2C::I2C(PinName sda, PinName scl) :
00031     scl_pin(scl), sda_pin(sda), frequency(10) {
00032         this->sda_pin.output();
00033         this->scl_pin.output();
00034     }
00035 
00036     void
00037     I2C::setFrequency(uint32_t hz) {
00038         this->frequency = (1000000 / hz);
00039     }
00040 
00041     void
00042     I2C::start(void) {
00043         this->output();
00044         this->sda(1);
00045         this->scl(1);
00046         this->sda(0);
00047         this->scl(0);
00048         this->scl(1);
00049         this->sda(1);
00050         this->scl(0);
00051     }
00052 
00053     void
00054     I2C::stop(void) {
00055         this->output();
00056         this->sda(0);
00057         this->scl(1);
00058         this->sda(1);
00059     }
00060 
00061     bool
00062     I2C::wait(void) {
00063         bool ack = false;
00064     
00065         this->input();
00066         for (uint8_t i = 0; i < 500 && !ack; i++) {
00067             wait_ms(1);
00068             ack = !this->sda_pin;
00069         }
00070     
00071         return ack;
00072     }
00073     
00074     void
00075     I2C::reset(void) {
00076         this->output();
00077         for (uint8_t i = 9; i; i--) {
00078             this->shift_out(1);
00079         }
00080         this->start();
00081         this->scl(1);
00082     }
00083 
00084     bool
00085     I2C::write(uint8_t data) {
00086         bool ack;
00087 
00088         this->output();
00089         for (uint8_t i = 8; i; i--) {
00090             this->shift_out(data & 0x80);
00091             data <<= 1;
00092         }
00093     
00094         this->input();
00095         ack = !this->shift_in();
00096     
00097         return ack;
00098     }
00099 
00100     uint8_t
00101     I2C::read(bool ack) {
00102         uint8_t data = 0;
00103     
00104         this->input();
00105         for (uint8_t i = 8; i; i--) {
00106             data <<= 1;
00107             data  |= this->shift_in();
00108         }
00109     
00110         this->output();
00111         this->shift_out(!ack);
00112     
00113         return data;
00114     }
00115 
00116     void
00117     I2C::output(void) {
00118         this->sda_pin.output();
00119     }
00120 
00121     void
00122     I2C::input(void) {
00123         this->sda_pin.input();
00124     }
00125 
00126     void
00127     I2C::sda(bool value) {
00128         this->sda_pin = value;
00129         wait_us(this->frequency);
00130     }
00131 
00132     void
00133     I2C::scl(bool value) {
00134         this->scl_pin = value;
00135         wait_us(this->frequency);
00136     }
00137 
00138     void
00139     I2C::shift_out(bool bit) {
00140         this->sda(bit);
00141         this->scl(1);
00142         this->scl(0);
00143     }
00144 
00145     bool
00146     I2C::shift_in(void) {
00147         wait_us(this->frequency);
00148         this->scl(1);
00149         bool bit = this->sda_pin;
00150         this->scl(0);
00151         return bit;
00152     }
00153 }