ardupilot/libraries/AP_ADC/AP_ADC_ADS7844.cpp

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
 *       AP_ADC_ADS7844.cpp - ADC ADS7844 Library for Ardupilot Mega
 *       Code by Jordi Mu<EFBFBD>oz and Jose Julio. DIYDrones.com
 *
 *       Modified by John Ihlein 6 / 19 / 2010 to:
 *       1)Prevent overflow of adc_counter when more than 8 samples collected between reads.	Probably
 *               only an issue on initial read of ADC at program start.
 *       2)Reorder analog read order as follows:
 *               p, q, r, ax, ay, az
 *
 *       This library is free software; you can redistribute it and / or
 *               modify it under the terms of the GNU Lesser General Public
 *               License as published by the Free Software Foundation; either
 *               version 2.1 of the License, or (at your option) any later version.
 *
 *       External ADC ADS7844 is connected via Serial port 2 (in SPI mode)
 *       TXD2 = MOSI = pin PH1
 *       RXD2 = MISO = pin PH0
 *       XCK2 = SCK = pin PH2
 *       Chip Select pin is PC4 (33)	 [PH6 (9)]
 *       We are using the 16 clocks per conversion timming to increase efficiency (fast)
 *
 *       The sampling frequency is 1kHz (Timer2 overflow interrupt)
 *
 *       So if our loop is at 50Hz, our needed sampling freq should be 100Hz, so
 *       we have an 10x oversampling and averaging.
 *
 *       Methods:
 *               Init() : Initialization of interrupts an Timers (Timer2 overflow interrupt)
 *               Ch(ch_num) : Return the ADC channel value
 *
 *       // HJI - Input definitions.  USB connector assumed to be on the left, Rx and servo
 *       // connector pins to the rear.  IMU shield components facing up.  These are board
 *       // referenced sensor inputs, not device referenced.
 *       On Ardupilot Mega Hardware, oriented as described above:
 *       Chennel 0 : yaw rate, r
 *       Channel 1 : roll rate, p
 *       Channel 2 : pitch rate, q
 *       Channel 3 : x / y gyro temperature
 *       Channel 4 : x acceleration, aX
 *       Channel 5 : y acceleration, aY
 *       Channel 6 : z acceleration, aZ
 *       Channel 7 : Differential pressure sensor port
 *
 */
#include "AP_ADC_ADS7844.h"

extern "C" {
// AVR LibC Includes
#include <inttypes.h>
#include <stdint.h>
#include <avr/interrupt.h>
}
#if defined(ARDUINO) && ARDUINO >= 100
 #include "Arduino.h"
#else
 #include "WConstants.h"
#endif

// Commands for reading ADC channels on ADS7844
static const unsigned char adc_cmd[9]              = { 0x87, 0xC7, 0x97, 0xD7, 0xA7, 0xE7, 0xB7, 0xF7, 0x00 };

// the sum of the values since last read
static volatile uint32_t _sum[8];

// how many values we've accumulated since last read
static volatile uint16_t _count[8];

// variables to calculate time period over which a group of samples were collected
static volatile uint32_t _ch6_delta_time_start_micros = 0;  // time we start collecting sample (reset on update)
static volatile uint32_t _ch6_last_sample_time_micros = 0;  // time latest sample was collected

// TCNT2 values for various interrupt rates,
// assuming 256 prescaler. Note that these values
// assume a zero-time ISR. The actual rate will be a
// bit lower than this
#define TCNT2_781_HZ   (256-80)
#define TCNT2_1008_HZ  (256-62)
#define TCNT2_1302_HZ  (256-48)

static inline unsigned char ADC_SPI_transfer(unsigned char data)
{
    /* Put data into buffer, sends the data */
    UDR2 = data;
    /* Wait for data to be received */
    while ( !(UCSR2A & (1 << RXC2)) ) ;
    /* Get and return received data from buffer */
    return UDR2;
}


void AP_ADC_ADS7844::read(uint32_t tnow)
{
    uint8_t ch;

    bit_clear(PORTC, 4);                                                        // Enable Chip Select (PIN PC4)
    ADC_SPI_transfer(adc_cmd[0]);                                               // Command to read the first channel

    for (ch = 0; ch < 8; ch++) {
        uint16_t v;

        v = ADC_SPI_transfer(0) << 8;                    // Read first byte
        v |= ADC_SPI_transfer(adc_cmd[ch + 1]);          // Read second byte and send next command

        if (v & 0x8007) {
            // this is a 12-bit ADC, shifted by 3 bits.
            // if we get other bits set then the value is
            // bogus and should be ignored
            continue;
        }

        if (++_count[ch] == 0) {
            // overflow ... shouldn't happen too often
            // unless we're just not using the
            // channel. Notice that we overflow the count
            // to 1 here, not zero, as otherwise the
            // reader below could get a division by zero
            _sum[ch] = 0;
            _count[ch] = 1;
        }
        _sum[ch] += (v >> 3);
    }

    bit_set(PORTC, 4);                                          // Disable Chip Select (PIN PC4)

    // record time of this sample
    _ch6_last_sample_time_micros = micros();
}


// Constructors ////////////////////////////////////////////////////////////////
AP_ADC_ADS7844::AP_ADC_ADS7844()
{
}

// Public Methods //////////////////////////////////////////////////////////////
void AP_ADC_ADS7844::Init( AP_PeriodicProcess * scheduler )
{
    scheduler->suspend_timer();
    pinMode(ADC_CHIP_SELECT, OUTPUT);

    digitalWrite(ADC_CHIP_SELECT, HIGH);      // Disable device (Chip select is active low)

    // Setup Serial Port2 in SPI mode
    UBRR2 = 0;
    DDRH |= (1 << PH2);         // SPI clock XCK2 (PH2) as output. This enable SPI Master mode
    // Set MSPI mode of operation and SPI data mode 0.
    UCSR2C = (1 << UMSEL21) | (1 << UMSEL20);     // |(0 << UCPHA2) | (0 << UCPOL2);
    // Enable receiver and transmitter.
    UCSR2B = (1 << RXEN2) | (1 << TXEN2);
    // Set Baud rate
    UBRR2 = 2;          // SPI clock running at 2.6MHz

    // get an initial value for each channel. This ensures
    // _count[] is never zero
    for (uint8_t i=0; i<8; i++) {
        uint16_t adc_tmp;
        adc_tmp  = ADC_SPI_transfer(0) << 8;
        adc_tmp |= ADC_SPI_transfer(adc_cmd[i + 1]);
        _count[i] = 1;
        _sum[i]   = adc_tmp;
    }

    _ch6_last_sample_time_micros = micros();

    scheduler->resume_timer();
    scheduler->register_process( AP_ADC_ADS7844::read );

}

// Read one channel value
float AP_ADC_ADS7844::Ch(uint8_t ch_num)
{
    uint16_t count;
    uint32_t sum;

    // ensure we have at least one value
    while (_count[ch_num] == 0) /* noop */;

    // grab the value with interrupts disabled, and clear the count
    uint8_t oldSREG = SREG;
    cli();
    count = _count[ch_num];
    sum   = _sum[ch_num];
    _count[ch_num] = 0;
    _sum[ch_num]   = 0;

    SREG = oldSREG;

    return ((float)sum)/count;
}

// see if Ch6() can return new data
bool AP_ADC_ADS7844::new_data_available(const uint8_t *channel_numbers)
{
    uint8_t i;

    for (i=0; i<6; i++) {
        if (_count[channel_numbers[i]] == 0) {
            return false;
        }
    }
    return true;
}


// Read 6 channel values
// this assumes that the counts for all of the 6 channels are
// equal. This will only be true if we always consistently access a
// sensor by either Ch6() or Ch() and never mix them. If you mix them
// then you will get very strange results
uint32_t AP_ADC_ADS7844::Ch6(const uint8_t *channel_numbers, float *result)
{
    uint16_t count[6];
    uint32_t sum[6];
    uint8_t i;

    // ensure we have at least one value
    for (i=0; i<6; i++) {
        while (_count[channel_numbers[i]] == 0) /* noop */;
    }

    // grab the values with interrupts disabled, and clear the counts
    uint8_t oldSREG = SREG;
    cli();
    for (i=0; i<6; i++) {
        count[i] = _count[channel_numbers[i]];
        sum[i]   = _sum[channel_numbers[i]];
        _count[channel_numbers[i]] = 0;
        _sum[channel_numbers[i]]   = 0;
    }

    // calculate the delta time.
    // we do this before re-enabling interrupts because another sensor read could fire immediately and change the _last_sensor_time value
    uint32_t ret = _ch6_last_sample_time_micros - _ch6_delta_time_start_micros;
    _ch6_delta_time_start_micros = _ch6_last_sample_time_micros;

    SREG = oldSREG;

    // calculate averages. We keep this out of the cli region
    // to prevent us stalling the ISR while doing the
    // division. That costs us 36 bytes of stack, but I think its
    // worth it.
    for (i = 0; i < 6; i++) {
        result[i] = sum[i] / (float)count[i];
    }

    // return number of microseconds since last call
    return ret;
}

/// Get minimum number of samples read from the sensors
uint16_t AP_ADC_ADS7844::num_samples_available(const uint8_t *channel_numbers)
{
    // get count of first channel as a base
    uint16_t min_count = _count[channel_numbers[0]];

    // reduce to minimum count of all other channels
    for (uint8_t i=1; i<6; i++) {
        if (_count[channel_numbers[i]] < min_count) {
            min_count = _count[channel_numbers[i]];
        }
    }
    return min_count;
}