MSP430F5529: Convert and store 1k samples from ADC

Hi Caleb,

Thank you very much for your response. Based on your response, I tried implementing DMA but it appears I am missing something.

Here is the DMA setup done inside main:

/* Configure DMA to transfer A2 and A3 values from the ADC to RAM */
    DMACTL0 = DMA0TSEL_24;                       // ADC12IFGx triggers DMA0
    DMA0SA = ADC12MEM0;                          // Source address
    DMA0DA = &adc_values[0];                     // Destination address
    DMA0SZ = 2;                                  // Transfer 2 16 bit words per trigger

In the ADC12_ISR, I have the following line

DMA0CTL = DMADT_0 | DMADSTINCR_3 | DMASRCINCR_3 | DMAEN | DMAIE; // Single transfer, increment dest addr, enable DMA & interrupt

Here are the problems that I am facing for which I would highly appreciate your suggestions:

1. The main problem I have is that I have a function call inside the infinite while loop that sends these values. So I can't have ADC in repeated mode. ADC and DMA have to work in single mode, enabling each other's ISRs. If I understand it correctly, the flow should be like, ADC ISR->ADC_ISR invokes DMA_ISR->Value is copied from ADC12MEM0, thus clearing IFG flag of ADC->DMA_ISR exit->ADC_ISR exit->Function inside infinite while loop of main sends the value

   However, during debugging, DMA doesn't seem to be invoked at all.

2. "You can also setup the DMA to interrupt the CPU once it has moved 1000 conversions to RAM and then wake from LPM"

   As shown in my code, I am using a counter samples_count to take care of when 1000 samples are collected. Do you mean I need to move this to the DMA ISR (where I am currently doing nothing)? I am taking one sample from ADC and then moving it to the array using DMA. Can I still implement your suggestion in this scenario?

3. The following line shows warning

   DMA0SA = ADC12MEM0;

   warning #515-D: a value of type "unsigned int" cannot be assigned to an entity of type "__SFR_FARPTR"

   The same is the case for DMA0DA line as well.

Hi Caleb,

I really appreciate your help! I tried to incorporate the changes you have suggested while referring to the user's guide multiple times.

Here's how the ADC setup looks like with Repeat-single-channel conversion mode:

static void setup_ADC(void){
	ADC12CTL0 = ADC12SHT02 + ADC12MSC+ ADC12ON;					// Sampling time, ADC12 on
	ADC12CTL1 = ADC12SHP + ADC12SSEL_1 + ADC12CONSEQ_2;			// Use sampling timer; Pulse Sample Mode; ADC12SHT02 decides the interval of the sampling timer
																// ACLK (32.768 kHz) selected as the clock source // Repeat-single-channel
	ADC12IE = 0x01;												// Enable interrupt
	ADC12CTL0 |= ADC12ENC;
	P6SEL |= 0x01;                            // P6.0 ADC option select
}

The DMA setup with Repeated single transfer mode is like this:

static void setup_DMA(void){
	/* Configure DMA to transfer values from the ADC to RAM */
	DMACTL0 = DMA0TSEL_24;                               // ADC12IFGx triggers DMA0
	DMACTL4 = DMARMWDIS;                                 // Read-modify-write disable
	DMA0CTL &= ~DMAIFG;
	DMA0CTL = DMADT_4 | DMADSTINCR_3 | DMAEN | DMAIE;    // Repeated single transfer, increment dest addr, enable DMA & interrupt
	DMA0SZ = 1000;                                       // Transfer 2 16 bit words per trigger
	__data16_write_addr((unsigned short) &DMA0SA,(unsigned long) &ADC12MEM0);	        // Source block address
	__data16_write_addr((unsigned short) &DMA0DA,(unsigned long) &adc_values);		// Destination single address
}

Inside the main, they are called in this sequence:

       
	setup_ADC();
	setup_DMA();

	while(1){
		/* Start ADC*/
		ADC12CTL0 |= ADC12SC;                   // Start sampling/conversion

		__bis_SR_register(LPM0_bits + GIE);     // LPM0, ADC12_ISR will force exit
		__no_operation();                       // For debugger
	}

There is only one ISR that is 

#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=DMA_VECTOR
__interrupt void DMA_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(DMA_VECTOR))) DMA_ISR (void)
#else
#error Compiler not supported!
#endif
{
	switch(__even_in_range(DMAIV,16))
	{
	case 0: break;
	case 2:                                 // DMA0IFG = DMA Channel 0
		__bic_SR_register_on_exit(LPM0_bits);   // Exit active CPU
	case 4: break;                          // DMA1IFG = DMA Channel 1
	case 6: break;                          // DMA2IFG = DMA Channel 2
	case 8: break;                          // DMA3IFG = DMA Channel 3
	case 10: break;                         // DMA4IFG = DMA Channel 4
	case 12: break;                         // DMA5IFG = DMA Channel 5
	case 14: break;                         // DMA6IFG = DMA Channel 6
	case 16: break;                         // DMA7IFG = DMA Channel 7
	default: break;
	}
}

I have the following problems now and would be thankful to have your suggestions/pointers on the same:

1. The debugger gets stuck at the following line inside main and never goes to the ISR. (There is only DMA_ISR in the code.)

__bis_SR_register(LPM0_bits + GIE);

The same happens with MSP430F55xx_dma_04.c example as well.

2. Since DMAEAN=1 as well as ADC12IFG0 gets set, shouldn't DMA_ISR get called? Do I need to enable/set something else as well?

3. "Inside the interrupt I recommend disabling the ADC"

So if I understand correctly, inside the DMA_ISR, I need to do something like clearing ADC12ENC bit.

Feedback on Documentation:
In the page 390 of slau208p, the section "11.2.3 Initiating DMA Transfers" says " The DMAxTSEL bits should be modified only when the DMACTLx DMAEN bit is 0." I think it should be DMAxCTL DMAEN instead.

Hi Caleb,

Yes, it worked! Thank you very much for that.

Now I am working on making the best of MSP430 power saving as well as efficiency. However these are the hurdles that I'm currently facing:

1. I was able to read the values through DMA, however the code seems to be very slow.  I am sharing the recent code to show this problem. The output "Inside main" shows up on the serial monitor like once in a second.

while(1){
		CLI_Write((_u8 *)" Inside main \n\r");
		DMA0SZ = 1000;                                 // Transfer 2 16 bit words per trigger
		/* Read ADC values*/
		ADC12CTL0 |= ADC12ENC | ADC12SC;		// Enable and Start sampling/conversion
		__bis_SR_register(LPM0_bits + GIE);     // LPM0, DMA_ISR will force exit
		__no_operation();                       // For debugger
	}

The ADC and DMA settings being as follows

static void setup_DMA(void){
	/* Configure DMA to transfer values from the ADC to RAM */
	DMA0CTL &= ~DMAEN;/* DMAxTSEL should by modified only when the DMACTLx DMAEN bit is 0 */
	if(~DMAEN){
		DMACTL0 = DMA0TSEL_24;                       // ADC12IFGx triggers DMA0
	}else{
		CLI_Write((_u8 *)" Cannot modify DMAxTSEL. DMA already enabled \n\r");
	}
	DMACTL4 = DMARMWDIS;                      // Read-modify-write disable
	DMA0CTL &= ~DMAIFG;
	DMA0CTL = DMADT_4 | DMADSTINCR_3 | DMAEN | DMAIE; // Repeated single transfer, increment dest addr, enable DMA & interrupt
	__data16_write_addr((unsigned short) &DMA0SA,(unsigned long) &ADC12MEM0);	// Source block address
	__data16_write_addr((unsigned short) &DMA0DA,(unsigned long) &adc_values);		// Destination single address
}

static void setup_ADC(void){
	ADC12CTL0 = ADC12SHT0_0 | ADC12MSC | ADC12ON;					// Sampling time, multiple sample and conversion, ADC12 on
	ADC12CTL1 = ADC12SHP | ADC12SSEL_1 | ADC12DIV1 | ADC12CONSEQ_2;			// Use sampling timer; Pulse Sample Mode; ADC12SHT02 decides the interval of the sampling timer
	// ACLK (32.768 kHz) selected as the clock source
	// Divide the clock by 2. New Clock becomes ACLK/2 around 16kHz
	// Repeat-single-channel
	P6SEL |= 0x01;                            // P6.0 ADC option select
}

Inside DMA ISR, I'm just enabling the ADC conversion with the following line

ADC12CTL0 &= ~ADC12ENC; // Disable conversion

2. In the ADC, I'm currently using ADC12SHT0_0. I understand that when ADC12SHP is set, i.e. Pulse Sample mode,  ADC12SHT0x decides the sampling timer interval. Which ADC12SHT0x should I use so that the sampling interval for SAMPCON would be just enough?

3. MCLK is disabled in LPM0, but DMA needs 2 MCLK cycles. So apparently it enables it without waking up the CPU and then disables. Doesn't it affect the efficiency? I am looking for optimizing the time my code stays in the Low power mode. If you have some guidelines for the same please let me know.

Hi Deepak, 

I wouldn't say your code is running slow, it just takes a while to sample, convert, then transfer 1000 samples to memory. Especially when your running the ADC at 16kHz as your comments above suggest. If you want your code to run faster you'll need to increase your ADC clock source and decrease the sample and hold time as much as possible. 

To reduce your sample and hold timing to a minimum, take a look at section 28.2.5.3 of the MSP430F5529 User's Guide. This short section describes how to calculate the minimum sampling time required for your application. 

Finally, using DMA is the best way to optimize for low power in this type of application. While it takes 2 MCLK cycles to transfer data, the CPU remains in LPM0 during the transfers.

Best regards, 
Caleb Overbay

Hi Caleb,

I'm really sorry I thought I have already shared updates with you, but I was wrong. Everything worked great! 

I would like to thank you once again for all the help you have provided to make the best use of MSP430 in my project.

Best Regards,

Deepak Koranga