mirror of https://github.com/ArduPilot/ardupilot
216 lines
6.2 KiB
C++
216 lines
6.2 KiB
C++
/*
|
||
AP_ADC_ADS7844.cpp - ADC ADS7844 Library for Ardupilot Mega
|
||
Code by Jordi Mu<4D>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
|
||
|
||
*/
|
||
extern "C" {
|
||
// AVR LibC Includes
|
||
#include <inttypes.h>
|
||
#include <stdint.h>
|
||
#include <avr/interrupt.h>
|
||
#include "WConstants.h"
|
||
}
|
||
|
||
#include "AP_ADC_ADS7844.h"
|
||
|
||
|
||
// 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];
|
||
|
||
static uint32_t last_ch6_micros;
|
||
|
||
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;
|
||
}
|
||
|
||
|
||
ISR (TIMER2_OVF_vect)
|
||
{
|
||
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 count = _count[ch];
|
||
uint32_t sum = _sum[ch];
|
||
|
||
if (++count == 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 = 0;
|
||
count = 1;
|
||
last_ch6_micros = micros();
|
||
}
|
||
_count[ch] = count;
|
||
|
||
sum += ADC_SPI_transfer(0) << 8; // Read first byte
|
||
sum += ADC_SPI_transfer(adc_cmd[ch + 1]); // Read second byte and send next command
|
||
|
||
_sum[ch] = sum;
|
||
}
|
||
|
||
bit_set(PORTC, 4); // Disable Chip Select (PIN PC4)
|
||
TCNT2 = 200;
|
||
}
|
||
|
||
|
||
// Constructors ////////////////////////////////////////////////////////////////
|
||
AP_ADC_ADS7844::AP_ADC_ADS7844()
|
||
{
|
||
}
|
||
|
||
// Public Methods //////////////////////////////////////////////////////////////
|
||
void AP_ADC_ADS7844::Init(void)
|
||
{
|
||
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;
|
||
}
|
||
|
||
last_ch6_micros = micros();
|
||
|
||
// Enable Timer2 Overflow interrupt to capture ADC data
|
||
TIMSK2 = 0; // Disable interrupts
|
||
TCCR2A = 0; // normal counting mode
|
||
TCCR2B = _BV(CS21) | _BV(CS22); // Set prescaler of 256
|
||
TCNT2 = 0;
|
||
TIFR2 = _BV(TOV2); // clear pending interrupts;
|
||
TIMSK2 = _BV(TOIE2) ; // enable the overflow interrupt
|
||
}
|
||
|
||
// Read one channel value
|
||
uint16_t 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
|
||
cli();
|
||
count = _count[ch_num];
|
||
sum = _sum[ch_num];
|
||
_count[ch_num] = 0;
|
||
_sum[ch_num] = 0;
|
||
sei();
|
||
|
||
return sum/count;
|
||
}
|
||
|
||
// 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, uint16_t *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
|
||
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;
|
||
}
|
||
sei();
|
||
|
||
// 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] / count[i];
|
||
}
|
||
|
||
// return number of microseconds since last call
|
||
uint32_t us = micros();
|
||
uint32_t ret = us - last_ch6_micros;
|
||
last_ch6_micros = us;
|
||
return ret;
|
||
}
|