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change ADC sample rate to 1kHz 

this costs us about 9% of our CPU, but should make aliasing much less
of a problem.
This commit is contained in:
Andrew Tridgell 2011-09-15 18:45:51 +10:00
parent 55bcb8a1c0
commit 1c5e8f0381
7 changed files with 90 additions and 83 deletions
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5
libraries/AP_ADC/AP_ADC.h
View File

@ -33,10 +33,11 @@ class AP_ADC
Pass in an array of 6 channel numbers and results are
returned in result[]
The function returns the amount of time that the returned
value has been averaged over, in 2.5 millisecond units
The function returns the amount of time (in microseconds)
since the last call to Ch6().
*/
virtual uint32_t Ch6(const uint8_t *channel_numbers, uint16_t *result) = 0;
private:
};

134
libraries/AP_ADC/AP_ADC_ADS7844.cpp
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@ -19,9 +19,11 @@
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 400Hz (Timer2 overflow interrupt)
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 4x oversampling and averaging.
we have an 10x oversampling and averaging.
Methods:
Init() : Initialization of interrupts an Timers (Timer2 overflow interrupt)
@ -60,14 +62,14 @@ static volatile uint32_t _sum[8];
// how many values we've accumulated since last read
static volatile uint16_t _count[8];
static unsigned char ADC_SPI_transfer(unsigned char data)
{
/* Wait for empty transmit buffer */
while ( !( UCSR2A & (1 << UDRE2)) );
/* Put data into buffer, sends the data */
UDR2 = data;
/* Wait for data to be received */
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;
@ -75,38 +77,39 @@ static unsigned char ADC_SPI_transfer(unsigned char data)
ISR (TIMER2_OVF_vect)
{
uint8_t ch;
//bit_set(PORTL,6); // To test performance
{
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 adc_tmp;
adc_tmp = ADC_SPI_transfer(0) << 8; // Read first byte
adc_tmp |= ADC_SPI_transfer(adc_cmd[ch + 1]); // Read second byte and send next command
_count[ch]++;
if (_count[ch] == 0) {
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[ch] = 0;
_count[ch] = 1;
sum = 0;
count = 1;
last_ch6_micros = micros();
}
_sum[ch] += adc_tmp;
}
_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)
//bit_clear(PORTL,6); // To test performance
TCNT2 = 104; // 400Hz interrupt
}
TCNT2 = 200;
}
// Constructors ////////////////////////////////////////////////////////////////
AP_ADC_ADS7844::AP_ADC_ADS7844()
{
@ -114,21 +117,21 @@ 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
{
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++) {
@ -139,17 +142,18 @@ void AP_ADC_ADS7844::Init(void)
_sum[i] = adc_tmp;
}
// 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
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;
@ -174,7 +178,7 @@ uint16_t AP_ADC_ADS7844::Ch(uint8_t ch_num)
// 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
uint16_t AP_ADC_ADS7844::Ch6(const uint8_t *channel_numbers, uint16_t *result)
uint32_t AP_ADC_ADS7844::Ch6(const uint8_t *channel_numbers, uint16_t *result)
{
uint16_t count[6];
uint32_t sum[6];
@ -203,7 +207,9 @@ uint16_t AP_ADC_ADS7844::Ch6(const uint8_t *channel_numbers, uint16_t *result)
result[i] = sum[i] / count[i];
}
// this assumes the count in all channels is equal, which will
// be true if the callers are using the interface consistently
return count[0];
}
// return number of microseconds since last call
uint32_t us = micros();
uint32_t ret = us - last_ch6_micros;
last_ch6_micros = us;
return ret;
}

8
libraries/AP_ADC/AP_ADC_ADS7844.h
View File

@ -24,9 +24,9 @@ class AP_ADC_ADS7844 : public AP_ADC
uint16_t Ch(unsigned char ch_num);
// Read 6 sensors at once
uint16_t Ch6(const uint8_t *channel_numbers, uint16_t *result);
private:
};
uint32_t Ch6(const uint8_t *channel_numbers, uint16_t *result);
private:
};
#endif

6
libraries/AP_ADC/AP_ADC_HIL.cpp
View File

@ -47,11 +47,11 @@ void AP_ADC_HIL::Init(void)
uint16_t AP_ADC_HIL::Ch(unsigned char ch_num)
{
return adcValue[ch_num];
}
}
// Read 6 channel values
uint16_t AP_ADC_HIL::Ch6(const uint8_t *channel_numbers, uint16_t *result)
{
uint32_t AP_ADC_HIL::Ch6(const uint8_t *channel_numbers, uint16_t *result)
{
for (uint8_t i=0; i<6; i++) {
result[i] = Ch(channel_numbers[i]);
}

10
libraries/AP_ADC/AP_ADC_HIL.h
View File

@ -34,12 +34,12 @@ class AP_ADC_HIL : public AP_ADC
// Read the sensor, part of public AP_ADC interface
uint16_t Ch(unsigned char ch_num);
///
///
// Read 6 sensors at once
uint16_t Ch6(const uint8_t *channel_numbers, uint16_t *result);
///
// Set the adc raw values given the current rotations rates,
uint32_t Ch6(const uint8_t *channel_numbers, uint16_t *result);
///
// Set the adc raw values given the current rotations rates,
// temps, accels, and pressures
void setHIL(int16_t p, int16_t q, int16_t r, int16_t gyroTemp,
int16_t aX, int16_t aY, int16_t aZ, int16_t diffPress);

2
libraries/AP_IMU/AP_IMU_Oilpan.cpp
View File

@ -279,7 +279,7 @@ AP_IMU_Oilpan::update(void)
int tc_temp = _adc->Ch(_gyro_temp_ch);
uint16_t adc_values[6];
_ticks = _adc->Ch6(_sensors, adc_values);
_sample_time = _adc->Ch6(_sensors, adc_values);
// convert corrected gyro readings to delta acceleration
//

8
libraries/AP_IMU/IMU.h
View File

@ -81,7 +81,7 @@ public:
///
/// @returns number of seconds
///
float get_delta_time(void) { return _ticks * (2.5/1000.0); }
float get_delta_time(void) { return _sample_time * 1.0e-6; }
/// A count of bad sensor readings
///
@ -98,9 +98,9 @@ protected:
/// Most recent gyro reading obtained by ::update
Vector3f _gyro;
/// number of 2.5ms ticks that the accel and gyro values
/// were calculated from
uint16_t _ticks;
/// number of microseconds that the accel and gyro values
/// were sampled over
uint32_t _sample_time;
};
#endif