How to make my ADC work in tm4c123gxl microcontroller? - arm

Question

My steps are as follows:
enabling clock for ADC and port of AIN10 (PB4).
Disabling the respective bits in DEN and DIR register corresponding to pin B4.
Enabling the corresponding pins in AFSEL register and PCTL register*.
Setting the registers for: Sampling rate,priority(SS3) etc as shown in the code.
Then I trigger it in another function but somehow my ADC isn't reading any other value of applied voltage.
My first question is about PCTL and what value we need to enable ADC on it?
I have been trying to solve it for about a day now but I still haven't figured it out yet. Any help is much appreciated.
// Register definitions for clock enable
#define SYSCTL_RCGCGPIO_R ( * ( ( volatile unsigned long *) 0x400FE608 ) )
#define SYSCTL_RCGCADC_R ( * ( ( volatile unsigned long *) 0x400FE638 ) )
#define GPIO_PORTB_AFSEL_R ( * ( ( volatile unsigned long *) 0x40058420 ) )
#define GPIO_PORTB_PCTL_R (*(( volatile unsigned long *)0x4005952C))
// Register definitions for GPIO port B ;;;;; AIN10 = PB4
#define GPIO_PORTB_DATA_R ( * ( ( volatile unsigned long *) 0x400053FC) )
#define GPIO_PORTB_DIR_R ( * ( ( volatile unsigned long *) 0x40005400 ) )
#define GPIO_PORTB_DEN_R ( *( ( volatile unsigned long *) 0x4000551C) )
// Register definitions for ADC0 and Sample Sequencer 3
#define ADC0_PC_R ( * ( ( volatile unsigned long *) 0x40038FC4 ) )
#define ADC0_SSPRI_R ( * ( ( volatile unsigned long *) 0x40038020 ) )
#define ADC0_ACTSS_R ( * ( ( volatile unsigned long *) 0x40038000 ) )
#define ADC0_IM_R ( * ( ( volatile unsigned long *) 0x40038008 ) )
#define ADC0_RIS_R ( * ( ( volatile unsigned long *) 0x40038004 ) )
#define ADC0_ISC_R ( * ( ( volatile unsigned long *) 0x4003800C) )
#define ADC0_SAC_R ( * ( ( volatile unsigned long *) 0x40038030 ) )
#define ADC0_PSSI_R ( * ( ( volatile unsigned long *) 0x40038028 ) )
#define ADC0_SSCTL3_R ( * ( ( volatile unsigned long *) 0x400380A4 ) )
#define ADC0_SSFIFO3_R ( * ( ( volatile unsigned long *) 0x400380A8 ) )
unsigned char Lookup_7Seg_Disp [ 12 ] = {0xC0 , 0xF9 , 0xA4 , 0xB0 , 0x99 ,
0x92 , 0x82 , 0xF8 , 0x80 , 0x90 , 0xC6};
unsigned char Temperature_Value [ 3 ] = {0 , 0 , 0xA} ;
unsigned char i , value=0;
unsigned int ADC_value = 0 , voltage = 0 ;
int maxVoltage=0;
void ADC_Init() {
volatile unsigned long delay;
SYSCTL_RCGCGPIO_R |= 0x01; //Enable Clock for Port A
SYSCTL_RCGCADC_R |= 0x1; //Enable ADC0
delay = SYSCTL_RCGCGPIO_R; //Delay for clock to settle down
GPIO_PORTB_DIR_R &= ~(0x10);//PB4 as input
GPIO_PORTB_DEN_R &= ~(0x10);//PB4 as analog type
GPIO_PORTB_AFSEL_R |= 0x10;
GPIO_PORTB_PCTL_R |= 0x10;
//Clear sampling rate
ADC0_PC_R &= 0x00;
//Set sampling rate to 125ksps
ADC0_PC_R &= 0x01;
//Set priority to SSFI3
ADC0_SSPRI_R |= 0x3210;
//Disable sample sequence 3 befor configuration
ADC0_ACTSS_R &= ~0x8;
//Enable TS0, IE0 and END0 bits
ADC0_SSCTL3_R |= 0xE;
//Enable 16x hardware oversampling
ADC0_SAC_R |= 0x4;
//Disable Interrupt by writing 0 to corresponding bit
ADC0_IM_R &= ~(0x8);
//Activate sample sequencer
ADC0_ACTSS_R |= 0x8;
}
void SystemInit() {
}
void ADC_Voltage(void) {
ADC0_PSSI_R |= 0x8;
while ((ADC0_RIS_R & 0x8)==0);
ADC_value = (ADC0_SSFIFO3_R & 0xFFF);
voltage = (ADC_value)*44;
if(voltage>maxVoltage){
maxVoltage=voltage;
}
ADC0_ISC_R |= 0x08;
}
void delay(unsigned long counter) {
int i;
for(i=0;i<counter;i++)
{}
}
int main(void) {
ADC_Init();
delay(1000);
ADC_Voltage();
maxVoltage=maxVoltage*0.707;
}

Answer 1

I'm not sure if you solved this yet. I typically use TI's supplied driverlib that you can find in TivaWARE, so I don't know all the registers for doing this DRM off the top of my head. Double check that you are muxing the pin properly. The other thing to look at is the sample sequencer. The ADCs are on sample sequencers and you have to set them up as well, for the number of samples, the source of the samples, etc. You can test your ADC configuration by setting up the sequencer to read from the internal temperature sensor instead of an external pin to at least get that section of the code debugged. If that works, and you then switch it to an external pin and it doesn't work anymore, then you'll know the problem is the pin muxing.
Is there a compelling reason you aren't using TI's supplied driver library? It would have taken minutes to set up by using that instead of performing DRM. if code size is a concern, the tm4c also has driverlib on ROM
Even if you cannot use driverlib for some reason, take a look at the driverlib source, the tivaware peripheral driver library user guide and the example code. You'll see the driverlib calls that are required to set this up, and can track that back to the registers that need configuring.