firmware/target/arm/s3c2440/adc-s3c2440.c

   1 /***************************************************************************
   2  *             __________               __   ___.
   3  *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
   4  *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
   5  *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
   6  *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
   7  *                     \/            \/     \/    \/            \/
   8  * $Id$
   9  *
  10  * Copyright (C) 2006 by Wade Brown
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
  18  * KIND, either express or implied.
  19  *
  20  ****************************************************************************/
  21 #include "cpu.h"
  22 #include "system.h"
  23 #include "adc.h"
  24 #include "adc-target.h"
  25 #include "kernel.h"
  26
  27 #ifdef MINI2440
  28 #include "touchscreen-target.h"
  29 #endif
  30
  31 static unsigned short adc_readings[NUM_ADC_CHANNELS];
  32
  33 /* prototypes */
  34 static unsigned short __adc_read(int channel);
  35 static void adc_tick(void);
  36
  37 void adc_init(void)
  38 {
  39     int i;
  40
  41     /* Turn on the ADC PCLK */
  42     s3c_regset32(&CLKCON, 1<<15);
  43
  44     /* Set channel 0, normal mode, disable "start by read" */
  45     ADCCON &= ~(0x3F);
  46
  47     /* No start delay.  Use normal conversion mode. */
  48     ADCDLY = 0x1;
  49
  50     /* Set and enable the prescaler */
  51     ADCCON = (ADCCON & ~(0xff<<6)) | (0x19<<6);
  52     ADCCON |= (1<<14);
  53
  54     /* prefill the adc channels */
  55     for (i = 0; i < NUM_ADC_CHANNELS; i++)
  56     {
  57         adc_readings[i] = __adc_read(i);
  58     }
  59
  60     /* start at zero so when the tick starts it is at zero */
  61     adc_readings[0] = __adc_read(0);
  62
  63     /* attach the adc reading to the tick */
  64     tick_add_task(adc_tick);
  65 }
  66
  67 /* Called to get the recent ADC reading */
  68 inline unsigned short adc_read(int channel)
  69 {
  70     return adc_readings[channel];
  71 }
  72
  73 /**
  74   * Read the ADC by polling
  75   * @param channel The ADC channel to read
  76   * @return 10bit reading from ADC channel or ADC_READ_ERROR if timeout
  77   */
  78 static unsigned short __adc_read(int channel)
  79 {
  80     int i;
  81
  82     /* Set the channel */
  83     ADCCON = (ADCCON & ~(0x7<<3)) | (channel<<3);
  84
  85     /* Start the conversion process */
  86     ADCCON |= 0x1;
  87
  88     /* Wait for a low Enable_start */
  89     for (i = 20000;;)
  90     {
  91         if(0 == (ADCCON & 0x1))
  92         {
  93             break;
  94         }
  95         else
  96         {
  97             i--;
  98             if (0 == i)
  99             {
 100                 /* Ran out of time */
 101                 return ADC_READ_ERROR;
 102             }
 103         }
 104     }
 105
 106     /* Wait for high End_of_Conversion */
 107     for(i = 20000;;)
 108     {
 109         if(ADCCON & (1<<15))
 110         {
 111             break;
 112         }
 113         else
 114         {
 115             i--;
 116             if(0 == i)
 117             {
 118                 /* Ran out of time */
 119                 return ADC_READ_ERROR;
 120             }
 121         }
 122     }
 123     return (ADCDAT0 & 0x3ff);
 124 }
 125
 126 /* add this to the tick so that the ADC converts are done in the background */
 127 static void adc_tick(void)
 128 {
 129     static unsigned channel=0;
 130
 131     /* Check if the End Of Conversion is set */
 132     if (ADCCON & (1<<15))
 133     {
 134         adc_readings[channel] = (ADCDAT0 & 0x3FF);
 135         if (++channel >= NUM_ADC_CHANNELS)
 136         {
 137             channel = 0;
 138         }
 139 #ifdef MINI2440
 140         /* interleave a touchscreen read if neccessary */
 141         touchscreen_scan_device();
 142 #endif
 143         /* setup the next conversion and start it*/
 144         ADCCON = (ADCCON & ~(0x7<<3)) | (channel<<3) | 0x01;
 145     }
 146 }
 147