analogin_api.c

00001 /* mbed Microcontroller Library
00002  * Copyright (c) 2006-2013 ARM Limited
00003  *
00004  * Licensed under the Apache License, Version 2.0 (the "License");
00005  * you may not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  *     http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an "AS IS" BASIS,
00012  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 #include "analogin_api.h"
00017 #include "cmsis.h"
00018 #include "pinmap.h"
00019 #include "error.h"
00020 
00021 #define ANALOGIN_MEDIAN_FILTER      1
00022 
00023 #define ADC_10BIT_RANGE             0x3FF
00024 #define ADC_12BIT_RANGE             0xFFF
00025 
00026 static inline int div_round_up(int x, int y) {
00027   return (x + (y - 1)) / y;
00028 }
00029 
00030 static const PinMap PinMap_ADC[] = {
00031     {P0_23, ADC0_0, 1},
00032     {P0_24, ADC0_1, 1},
00033     {P0_25, ADC0_2, 1},
00034     {P0_26, ADC0_3, 1},
00035     {P1_30, ADC0_4, 3},
00036     {P1_31, ADC0_5, 3},
00037     {NC,    NC,     0}
00038 };
00039 
00040 #define ADC_RANGE    ADC_10BIT_RANGE
00041 
00042 
00043 void analogin_init(analogin_t *obj, PinName pin) {
00044     obj->adc = (ADCName)pinmap_peripheral(pin, PinMap_ADC);
00045     if (obj->adc == (uint32_t)NC) {
00046         error("ADC pin mapping failed");
00047     }
00048     
00049     // ensure power is turned on
00050     LPC_SC->PCONP |= (1 << 12);
00051     
00052     // set PCLK of ADC to /1
00053     LPC_SC->PCLKSEL0 &= ~(0x3 << 24);
00054     LPC_SC->PCLKSEL0 |= (0x1 << 24);
00055     uint32_t PCLK = SystemCoreClock;
00056     
00057     // calculate minimum clock divider
00058     //  clkdiv = divider - 1
00059     uint32_t MAX_ADC_CLK = 13000000;
00060     uint32_t clkdiv = div_round_up(PCLK, MAX_ADC_CLK) - 1;
00061     
00062     // Set the generic software-controlled ADC settings
00063     LPC_ADC->ADCR = (0 << 0)      // SEL: 0 = no channels selected
00064                   | (clkdiv << 8) // CLKDIV: PCLK max ~= 25MHz, /25 to give safe 1MHz at fastest
00065                   | (0 << 16)     // BURST: 0 = software control
00066                   | (0 << 17)     // CLKS: not applicable
00067                   | (1 << 21)     // PDN: 1 = operational
00068                   | (0 << 24)     // START: 0 = no start
00069                   | (0 << 27);    // EDGE: not applicable
00070     
00071     pinmap_pinout(pin, PinMap_ADC);
00072 }
00073 
00074 static inline uint32_t adc_read(analogin_t *obj) {
00075     // Select the appropriate channel and start conversion
00076     LPC_ADC->ADCR &= ~0xFF;
00077     LPC_ADC->ADCR |= 1 << (int)obj->adc;
00078     LPC_ADC->ADCR |= 1 << 24;
00079     
00080     // Repeatedly get the sample data until DONE bit
00081     unsigned int data;
00082     do {
00083         data = LPC_ADC->ADGDR;
00084     } while ((data & ((unsigned int)1 << 31)) == 0);
00085     
00086     // Stop conversion
00087     LPC_ADC->ADCR &= ~(1 << 24);
00088     
00089     return (data >> 6) & ADC_RANGE; // 10 bit
00090 }
00091 
00092 static inline void order(uint32_t *a, uint32_t *b) {
00093     if (*a > *b) {
00094         uint32_t t = *a;
00095         *a = *b;
00096         *b = t;
00097     }
00098 }
00099 
00100 static inline uint32_t adc_read_u32(analogin_t *obj) {
00101     uint32_t value;
00102 #if ANALOGIN_MEDIAN_FILTER
00103     uint32_t v1 = adc_read(obj);
00104     uint32_t v2 = adc_read(obj);
00105     uint32_t v3 = adc_read(obj);
00106     order(&v1, &v2);
00107     order(&v2, &v3);
00108     order(&v1, &v2);
00109     value = v2;
00110 #else
00111     value = adc_read(obj);
00112 #endif
00113     return value;
00114 }
00115 
00116 uint16_t analogin_read_u16(analogin_t *obj) {
00117     uint32_t value = adc_read_u32(obj);
00118     
00119     return (value << 6) | ((value >> 4) & 0x003F); // 10 bit
00120 }
00121 
00122 float analogin_read(analogin_t *obj) {
00123     uint32_t value = adc_read_u32(obj);
00124     return (float)value * (1.0f / (float)ADC_RANGE);
00125 }