How to use STM32 as a logic analyzer?

You can turn an STM32 microcontroller into a basic logic analyzer to capture and analyze digital signals. Here's how to implement this:

Hardware Requirements

• STM32 board (F3/F4/H7 series recommended for better performance)

• Input protection circuitry (optional but recommended - diodes, resistors)

• Host computer for data analysis

Software Approaches

1. Using Serial Communication (Basic)

Method:

• Configure GPIO pins in input mode

• Sample inputs at fixed intervals

• Send data via UART/USB to PC

Example Code:

#define SAMPLE_PIN PA0
#define SAMPLE_RATE 100000 // 100 kHz

void setup() {
  pinMode(SAMPLE_PIN, INPUT);
  Serial.begin(115200);
}

void loop() {
  static uint32_t lastTime = 0;
  if (micros() - lastTime >= (1000000/SAMPLE_RATE)) {
    lastTime = micros();
    Serial.println(digitalRead(SAMPLE_PIN));
  }
}

2. Using Timer Interrupts (Better Performance)

volatile uint8_t samples[1000];
volatile uint16_t sampleIndex = 0;

void setup() {
  pinMode(PA0, INPUT);
  TIM_TypeDef *Instance = TIM2;
  HardwareTimer *MyTim = new HardwareTimer(Instance);
  MyTim->setOverflow(100000, HERTZ_FORMAT); // 100 kHz sampling
  MyTim->attachInterrupt(sampleISR);
  MyTim->resume();
}

void sampleISR() {
  if(sampleIndex < 1000) {
    samples[sampleIndex++] = digitalRead(PA0);
  }
}

void loop() {
  if(sampleIndex >= 1000) {
    for(int i=0; i<1000; i++) {
      Serial.println(samples[i]);
    }
    sampleIndex = 0;
  }
}

3. Using DMA (Highest Performance)

For STM32H7/F7/F4 with DMA:

• Configure timer to trigger DMA transfers

• DMA writes directly to memory buffer

• Can achieve 10-50 MHz sampling on multiple channels

PC-Side Visualization Options

1. Sigrok/PulseView:

   • Use the "serial" or "UART" input option

   • Configure baud rate and data format

2. Custom Python Script:

import serial
import matplotlib.pyplot as plt

ser = serial.Serial('COM3', 115200)
data = []
for _ in range(1000):
    data.append(int(ser.readline().decode().strip()))
    
plt.plot(data)
plt.show()

3. Arduino Serial Plotter:

• Simple but limited to slower sample rates

Advanced Techniques

1. Multiple Channels:

   • Use GPIO port input register to read up to 16 pins simultaneously

   • Example: uint16_t port_data = GPIOA->IDR;

2. Trigger Conditions:

   • Implement hardware/comparator based triggers

   • Capture pre-trigger and post-trigger data

3. Timing Accuracy:

   • Use hardware timers for precise sampling intervals

   • STM32's timer peripherals can trigger DMA transfers

Limitations

1. Speed Limits:

   • Basic methods: ~100 kHz

   • DMA methods: Up to ~50 MHz (depends on STM32 model)

2. Memory Constraints:

   • Limited by available RAM for sample storage

   • STM32F103: ~20KB max buffer

   • STM32H743: Up to 1MB possible

3. Voltage Levels:

   • STM32 is 3.3V only (need level shifting for 5V signals)