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   1 /*
   2  * Copyright © 2019 Keith Packard <keithp@keithp.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation, either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  */
  14
  15 #include <ao.h>
  16 #include <ao_adc-samd21.h>
  17
  18 static void
  19 ao_adc_sync(void)
  20 {
  21         while (samd21_adc.status & (1 << SAMD21_ADC_STATUS_SYNCBUSY))
  22                 ;
  23 }
  24
  25 static uint16_t
  26 ao_adc_do_conversion(void)
  27 {
  28         ao_adc_sync();
  29         samd21_adc.swtrig = (1 << SAMD21_ADC_SWTRIG_START);
  30         ao_adc_sync();
  31         while ((samd21_adc.intflag & (1 << SAMD21_ADC_INTFLAG_RESRDY)) == 0)
  32                 ao_adc_sync();
  33         ao_adc_sync();
  34         return samd21_adc.result;
  35 }
  36
  37 uint16_t
  38 ao_adc_read(uint8_t channel)
  39 {
  40         ao_adc_sync();
  41         samd21_adc.inputctrl = ((channel << SAMD21_ADC_INPUTCTRL_MUXPOS) |
  42                                 (SAMD21_ADC_INPUTCTRL_MUXNEG_GND << SAMD21_ADC_INPUTCTRL_MUXNEG) |
  43                                 (0 << SAMD21_ADC_INPUTCTRL_INPUTSCAN) |
  44                                 (0 << SAMD21_ADC_INPUTCTRL_INPUTOFFSET) |
  45                                 (SAMD21_ADC_INPUTCTRL_GAIN_DIV2 << SAMD21_ADC_INPUTCTRL_GAIN));
  46
  47         /* Read twice and discard the first value as recommended by app note
  48          * http://www.atmel.com/images/Atmel-42645-ADC-Configurations-with-Examples_ApplicationNote_AT11481.pdf
  49          */
  50         (void) ao_adc_do_conversion();
  51         return ao_adc_do_conversion();
  52 }
  53
  54 void
  55 ao_adc_init(void)
  56 {
  57         /* supply a clock */
  58         samd21_gclk_clkctrl(0, SAMD21_GCLK_CLKCTRL_ID_ADC);
  59
  60         /* enable the device */
  61         samd21_pm.apbcmask |= (1 << SAMD21_PM_APBCMASK_ADC);
  62
  63         /* Reset */
  64         samd21_adc.ctrla = (1 << SAMD21_ADC_CTRLA_SWRST);
  65
  66         ao_adc_sync();
  67
  68         while ((samd21_adc.ctrla & (1 << SAMD21_ADC_CTRLA_SWRST)) != 0 ||
  69                (samd21_adc.status & (1 << SAMD21_ADC_STATUS_SYNCBUSY)) != 0)
  70                 ao_adc_sync();
  71
  72         /* Load ADC calibration values */
  73         uint32_t b = (samd21_aux1.calibration >> SAMD21_AUX1_CALIBRATION_ADC_BIASCAL) & SAMD21_AUX1_CALIBRATION_ADC_BIASCAL_MASK;
  74         uint32_t l = (samd21_aux1.calibration >> SAMD21_AUX1_CALIBRATION_ADC_LINEARITY) & SAMD21_AUX1_CALIBRATION_ADC_LINEARITY_MASK;
  75
  76         samd21_adc.calib = ((b << SAMD21_ADC_CALIB_BIAS_CAL) |
  77                             (l << SAMD21_ADC_CALIB_LINEARITY_CAL));
  78
  79
  80         ao_adc_sync();
  81
  82         samd21_adc.ctrlb = ((0 << SAMD21_ADC_CTRLB_DIFFMODE) |
  83                             (0 << SAMD21_ADC_CTRLB_LEFTADJ) |
  84                             (0 << SAMD21_ADC_CTRLB_FREERUN) |
  85                             (0 << SAMD21_ADC_CTRLB_CORREN) |
  86                             (SAMD21_ADC_CTRLB_RESSEL_12BIT << SAMD21_ADC_CTRLB_RESSEL) |
  87                             (SAMD21_ADC_CTRLB_PRESCALER_DIV512 << SAMD21_ADC_CTRLB_PRESCALER));
  88
  89         ao_adc_sync();
  90
  91         samd21_adc.sampctrl = 0x1f;
  92
  93         ao_adc_sync();
  94
  95         samd21_adc.refctrl = (SAMD21_ADC_REFCTRL_REFSEL_INTVCC1 << SAMD21_ADC_REFCTRL_REFSEL);
  96
  97         ao_adc_sync();
  98
  99         samd21_adc.ctrla = (1 << SAMD21_ADC_CTRLA_ENABLE);
 100 }