DMA with ADC for continuous sampling in Embedded C - Step-by-Step Execution

Concept Flow - DMA with ADC for continuous sampling

Start ADC Conversion

↓

ADC samples analog input

↓

ADC conversion complete interrupt triggers

↓

DMA transfers ADC data to memory buffer

↓

Check if buffer full

↓

Continue

↓

Restart ADC Conversion for next sample

The ADC continuously samples an analog input. Each conversion triggers DMA to transfer data to memory. When the buffer fills, data is processed, and sampling continues.

Execution Sample

Embedded C

void setup() {
  ADC_Start();
  DMA_Start(buffer, size);
}

void ADC_IRQHandler() {
  DMA_Transfer();
}

Starts ADC and DMA for continuous sampling; DMA transfers ADC data on each conversion interrupt.

Execution Table

Step	ADC State	DMA Action	Buffer Index	Buffer Full?	Next Action
1	Start conversion	Idle	0	No	Wait for conversion
2	Conversion complete	Transfer sample to buffer[0]	1	No	Start next conversion
3	Conversion complete	Transfer sample to buffer[1]	2	No	Start next conversion
4	Conversion complete	Transfer sample to buffer[2]	3	No	Start next conversion
5	Conversion complete	Transfer sample to buffer[3]	4	No	Start next conversion
6	Conversion complete	Transfer sample to buffer[4]	5	No	Start next conversion
7	Conversion complete	Transfer sample to buffer[5]	6	No	Start next conversion
8	Conversion complete	Transfer sample to buffer[6]	7	No	Start next conversion
9	Conversion complete	Transfer sample to buffer[7]	8	No	Start next conversion
10	Conversion complete	Transfer sample to buffer[8]	9	No	Start next conversion
11	Conversion complete	Transfer sample to buffer[9]	10	Yes	Process buffer and restart
12	Start conversion	Idle	0	No	Wait for conversion
Exit	Buffer processed	DMA reset buffer index	-	-	Continuous sampling continues

💡 Buffer reaches full size (10 samples), triggers processing, then sampling restarts.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10	Final
buffer_index	0	1	2	3	4	5	6	7	8	9	10	0
buffer_full	No	No	No	No	No	No	No	No	No	No	Yes	No

Key Moments - 3 Insights

Why does the buffer_index reset to 0 after reaching 10?

Because when the buffer is full (see step 11 in execution_table), the program processes the data and resets the index to start filling the buffer again for continuous sampling.

Does the ADC stop sampling when the buffer is full?

No, the ADC keeps sampling continuously. The DMA transfers data and the buffer is processed in the background, then sampling continues immediately (see steps 11 and 12).

What triggers the DMA to transfer data from ADC to memory?

Each ADC conversion complete interrupt triggers the DMA transfer, as shown in each 'Conversion complete' step in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what is the buffer_index after step 5?

A 5

B 4

C 3

D 6

💡 Hint

Check the 'Buffer Index' column at step 5 in the execution_table.

At which step does the buffer become full?

A Step 11

B Step 9

C Step 10

D Step 12

💡 Hint

Look for 'Buffer Full?' column showing 'Yes' in the execution_table.

If the buffer size was increased to 20, how would the buffer_index change at step 11?

A It would be 11

B It would be 20

C It would be 10

D It would reset to 0

💡 Hint

Refer to variable_tracker and execution_table logic for buffer_index increments.

Concept Snapshot

DMA with ADC for continuous sampling:
- ADC converts analog input continuously.
- Each conversion triggers DMA to transfer data to a memory buffer.
- Buffer index increments with each sample.
- When buffer is full, data is processed and buffer resets.
- Sampling and DMA transfer continue without CPU blocking.

Full Transcript

This visual execution shows how DMA works with ADC for continuous sampling. The ADC starts converting analog signals. When a conversion finishes, an interrupt triggers DMA to move the data to a buffer in memory. The buffer index increases by one each time. When the buffer fills up, the program processes the data and resets the buffer index to zero. Then the ADC continues sampling and DMA transfers data again. This cycle repeats continuously without stopping the CPU. The execution table tracks each step, showing ADC state, DMA action, buffer index, and whether the buffer is full. The variable tracker shows how buffer_index and buffer_full change over time. Key moments clarify common confusions about buffer reset, continuous sampling, and DMA triggers. The quiz tests understanding of buffer indexing and buffer full conditions. This helps beginners see exactly how DMA and ADC work together for efficient continuous data sampling.