Logic analyzer for signal debugging in Embedded C - Step-by-Step Execution

Concept Flow - Logic analyzer for signal debugging

Start program

↓

Initialize hardware

↓

Configure input pin

↓

Enter loop

↓

Read signal state

↓

Store timestamp and state

↓

Check buffer full?

Yes→Process/Output data

No↓

Read signal state

The program initializes hardware, reads a digital signal repeatedly, stores the time and state, and outputs data when the buffer is full.

Execution Sample

Embedded C

void loop() {
  int state = digitalRead(signalPin);
  buffer[index++] = state;
  if (index == BUFFER_SIZE) {
    outputData();
    index = 0;
  }
}

This code reads a signal pin, stores the state in a buffer, and outputs data when the buffer is full.

Execution Table

Step	Action	Signal State Read	Buffer Index	Buffer Content	Condition	Next Action
1	Read signal	0	0	[ ]	index < BUFFER_SIZE	Store state, index=1
2	Read signal	1	1	[0]	index < BUFFER_SIZE	Store state, index=2
3	Read signal	1	2	[0,1]	index < BUFFER_SIZE	Store state, index=3
4	Read signal	0	3	[0,1,1]	index < BUFFER_SIZE	Store state, index=4
5	Read signal	1	4	[0,1,1,0]	index < BUFFER_SIZE	Store state, index=5
6	Read signal	0	5	[0,1,1,0,1]	index < BUFFER_SIZE	Store state, index=6
7	Read signal	1	6	[0,1,1,0,1,0]	index < BUFFER_SIZE	Store state, index=7
8	Read signal	0	7	[0,1,1,0,1,0,1]	index < BUFFER_SIZE	Store state, index=8
9	Read signal	1	8	[0,1,1,0,1,0,1,0]	index < BUFFER_SIZE	Store state, index=9
10	Read signal	0	9	[0,1,1,0,1,0,1,0,1]	index < BUFFER_SIZE	Store state, index=10
11	Read signal	1	10	[0,1,1,0,1,0,1,0,1,0]	index == BUFFER_SIZE	Call outputData(), reset index=0
12	Output data	-	-	-	-	Clear buffer, start new cycle

💡 Buffer full at step 11, data output triggered, index reset to 0

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6	After 7	After 8	After 9	After 10	After 11	Final
index	0	1	2	3	4	5	6	7	8	9	10	0	0
buffer	[]	[0]	[0,1]	[0,1,1]	[0,1,1,0]	[0,1,1,0,1]	[0,1,1,0,1,0]	[0,1,1,0,1,0,1]	[0,1,1,0,1,0,1,0]	[0,1,1,0,1,0,1,0,1]	[0,1,1,0,1,0,1,0,1,0]	cleared	[]

Key Moments - 3 Insights

Why does the index reset to 0 after reaching BUFFER_SIZE?

Because when index equals BUFFER_SIZE (step 11), the buffer is full and outputData() is called. Then index resets to 0 to start storing new data, as shown in execution_table row 11.

What happens if we don't reset the index after outputting data?

If index is not reset, new data would overwrite buffer out of bounds or cause errors. The program relies on resetting index to 0 to reuse the buffer safely, as seen in the variable_tracker.

Why do we store the signal state before checking the buffer full condition?

Storing the state first ensures no data is lost. The condition check happens after storing, so the buffer fills completely before output, as shown in execution_table steps 1-11.

Visual Quiz - 3 Questions

Look at the execution table, what is the buffer index at step 5?

A 4

B 5

C 3

D 6

💡 Hint

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

At which step does the condition 'index == BUFFER_SIZE' become true?

A Step 10

B Step 11

C Step 9

D Step 12

💡 Hint

Look at the 'Condition' column in the execution_table to find when index equals BUFFER_SIZE.

If the signal state read at step 3 changed from 1 to 0, how would the buffer content at step 3 change?

A [0,0]

B [0,1]

C [1,0]

D [1,1]

💡 Hint

Check the 'Buffer Content' column at step 3 and imagine replacing the signal state read with 0.

Concept Snapshot

Logic Analyzer Loop in Embedded C:
- Initialize hardware and input pin
- Loop: read signal state
- Store state in buffer at current index
- If buffer full (index == BUFFER_SIZE), output data and reset index
- Repeat to capture signal changes over time

Full Transcript

This program acts like a simple logic analyzer. It starts by setting up the hardware and input pin. Then it enters a loop where it reads the digital signal state from a pin. Each state is saved in a buffer at the current index. The index increases with each read. When the buffer is full, the program calls a function to output the collected data and resets the index to zero to start over. This cycle repeats, allowing the program to capture and store signal changes over time for debugging.