[digitaldcpower] / analog.c

/* vim: set sw=8 ts=8 si : */
/*********************************************
* Author: Guido Socher, Copyright: GPL 
*
* Digital analog conversion of channel ADC0 and ADC1 in
* free running mode. 
**********************************************/
#include <avr/interrupt.h>
#include <avr/io.h>
#include <inttypes.h>
#include <stdlib.h>
#include "dac.h"
#include "uart.h"
#include "hardware_settings.h"


//debug LED:
// set output to VCC, red LED off
#define LEDOFF PORTD|=(1<<PORTD0)
// set output to GND, red LED on
#define LEDON PORTD&=~(1<<PORTD0)
// to test the state of the LED
#define LEDISOFF PORTD&(1<<PORTD0)
static volatile uint8_t currentcontrol=1; // 0=voltage control, otherwise current control
// adc measurement results (11bit ADC):
static volatile int16_t analog_result[2];  


// target_val is the value that is requested (control loop calibrates to this).
// We use the same units a the ADC produces.
static volatile int16_t target_val[2];  // datatype int is 16 bit

static volatile int16_t dac_val=800; // the current dac setting

// You must enable interrupt with sei() in the main program 
// before you call init_analog 
void init_analog(void) 
{
        // initialize the adc result to very high values
        // to keep the control-loop down until proper measurements
        // are done:
        analog_result[0]=0; // I
        analog_result[1]=20;  // U
        target_val[0]=0; // initialize to zero, I
        target_val[1]=0; // initialize to zero, U
        /* enable analog to digital conversion in free run mode
        *  without noise canceler function. See datasheet of atmega8a page 210
        * We set ADPS2=1,ADPS1=1,ADPS0=0 to have a clock division factor of 64.
        * This is needed to stay in the recommended range of 50-200kHz 
        * ADEN: Analog Digital Converter Enable
        * ADIE: ADC Interrupt Enable
        * ADIF: ADC Interrupt Flag
        * ADFR: ADC Free Running Mode
        * ADCSR: ADC Control and Status Register
        * ADPS2..ADPS0: ADC Prescaler Select Bits
        * REFS: Reference Selection Bits (page 203)
        */

        // int-ref with external capacitor at AREF pin: 
        // 2.56V int ref=REFS1=1,REFS0=1
        // write only the lower 3 bit for channel selection
        
        // 2.56V ref, start with channel 0
        ADMUX=(1<<REFS1)|(1<<REFS0);

        ADCSR=(1<<ADEN)|(1<<ADIE)|(1<<ADFR)|(1<<ADIF)|(1<<ADPS2)|(1<<ADPS1)|(0<<ADPS0);

        //  start conversion 
        ADCSR|=(1<<ADSC);
}

int16_t get_dacval(void) 
{
        return(dac_val);
}

uint8_t is_current_limit(void) 
{
        // return 1 if current control loop active
        if (currentcontrol){
                return(1);
        }
        return(0);
}

/* set the target adc value for the control loop
 * values for item: 1 = u, 0 = i, units must be of the same as the values 
 * from the dac.
 */
void set_target_adc_val(uint8_t item,int16_t val) 
{
        // here we can directly write to target_val 
        target_val[item]=val;
}

int16_t getanalogresult(uint8_t channel) 
{
        return(analog_result[channel]);
}

// the control loop changes the dac:
static void control_loop(void){
        int16_t tmp;
        int8_t ptmp=0;
        tmp=target_val[0] - analog_result[0]; // current diff
        if (tmp <0){
                // stay in currnet control if we are
                // close to the target. We never regulate
                // the difference down to zero otherweise
                // we would suddenly hop to voltage control
                // and then back to current control. Permanent
                // hopping would lead to oscillation and current
                // spikes.
                if (tmp>-4) tmp=0;
                currentcontrol=40; // I control
                if (analog_result[1]>target_val[1]){
                        tmp=-20;
                        currentcontrol=0; // U control
                }
        }else{
                // if we are in current control then we can only go
                // down (tmp is negative). To increase the current
                // we come here to voltage control. We must slowly
                // count up.
                tmp=1 + target_val[1]  - analog_result[1]; // voltage diff
                //
                if (currentcontrol){
                        currentcontrol--;
                        if (currentcontrol%8==0){
                                // slowly up, 20 will become 1 further down
                                if (tmp>0) tmp=20;
                        }else{
                                tmp=0;
                        }
                }
        }
        if (tmp==0){
                return; // nothing to change
        }
        if (tmp> -5 && tmp<5){ // avoid LSB bouncing if we are close
                if (tmp>0){
                        ptmp++;
                        tmp=0;
                        if (ptmp>1){
                                tmp=1;
                                ptmp=0;
                        }
                }
                if (tmp<0){
                        ptmp--;
                        tmp=0;
                        if (ptmp<-1){
                                tmp=-1;
                                ptmp=0;
                        }
                }
        }
        // put a cap on increase
        if (tmp>1){
                tmp=1;
        }
        // put a cap on decrease
        if (tmp<-1){
                tmp=-1;
        }
        dac_val+=tmp;
        if (dac_val>0xFFF){
                dac_val=0xFFF; //max, 12bit
        }
        if (dac_val<400){  // the output is zero below 400 due to transistor threshold
                dac_val=400;
        }
        dac(dac_val);
}
/* the following function will be called when analog conversion is done.
 * It will be called every 13th cycle of the converson clock. At 8Mhz
 * and a ADPS factor of 64 this is: ((8000 kHz/ 64) / 13)= 9.6KHz intervalls
 *
 * We do 4 fold oversampling as explained in atmel doc AVR121.
 */
//SIGNAL(SIG_ADC) {
ISR(ADC_vect) {
        uint8_t i=0;
        uint8_t adlow;
        int16_t currentadc;
        static uint8_t channel=0; 
        static uint8_t chpos=0;
        // raw 10bit values:
        static int16_t raw_analog_u_result[8];  
        int16_t new_analog_u_result=0;
        adlow=ADCL; // read low first !! 
        currentadc=(ADCH<<8)|adlow;
        // toggel the channel between 0 an 1. This will however
        // not effect the next conversion as that one is already
        // ongoing.
        channel^=1;
        // 2.56V ref
        ADMUX=(1<<REFS1)|(1<<REFS0)|channel;
        // channel=1 = U, channel=0 = I
        if (channel==1) {
                raw_analog_u_result[chpos]=currentadc;
                //
                // we do 4 bit oversampling to get 11bit ADC resolution
                chpos=(chpos+1)%4; // rotate over 4 
                //analog_result[1]=0;
                while(i<4){
                        new_analog_u_result+=raw_analog_u_result[i];
                        i++;
                }
                new_analog_u_result=new_analog_u_result>>1; // 11bit
                // mean value:
                analog_result[1]=(new_analog_u_result+analog_result[1])/2; 
        }else{
                analog_result[0]=currentadc; // 10bit
        }
        // short circuit protection does not use the over sampling results
        // for speed reasons.
        // short circuit protection, current is 10bit ADC
        if (channel==0 && currentadc > SH_CIR_PROT){
                dac_val=400;
                dac(dac_val);
                currentcontrol=20;
                return;
        }
        //
        if (channel==1){
                // only after full measurement cycle
                control_loop();
        }else{
                uart_poll_getchar_isr();
        }
        // end of interrupt handler
}