关于ADC数据每秒10段存储至SD卡的定时器配置与分段传输问题

Let's break down your two key problems and give practical, embedded-friendly solutions that fit with your existing zero-crossing detection code.

1. Configuring a Timer to Achieve 10 Segments Per Second #

First, let's clarify the timing: 10 segments per second means we need to write one segment every 100ms (since 1000ms / 10 = 100ms). Here's how to implement this with a hardware timer (assuming you're using a microcontroller like STM32, Arduino, or similar):

• Calculate Timer Parameters:
  For a typical 72MHz system clock (adjust based on your MCU):

  • Prescaler: Set to 7199 (divides 72MHz down to 10kHz)
  • Auto-reload value: 999 (10kHz * 100ms = 1000 ticks, so 0-999 gives 100ms per interrupt)
    Note: Tweak these numbers to match your MCU's actual clock frequency.

• Set Up Timer Interrupt:
  Enable the timer's update interrupt. Don’t do the SD card write directly in the interrupt service routine (ISR)—SD operations are slow and will block critical timing. Instead:

  • Set a simple global flag (e.g., flag_write_segment = true)
  • Or push a "write request" to a lightweight queue (if you’re using an RTOS)

• Link with Your Zero-Crossing Code:
  Every time your zero-crossing function identifies a new data segment, store that segment in a thread-safe buffer (like a circular buffer). This ensures you have segments ready to write when the timer triggers.

2. Pausing After 10 Segments, Then Resuming #

You’ll need a counter to track batch progress, plus logic to pause and restart the timer:

• Add a Segment Counter:
  Declare a global or static variable (e.g., uint8_t segment_count = 0). Every time you successfully write a segment to SD:

  segment_count++;
  if (segment_count >= 10) {
    // Trigger pause
    HAL_TIM_Base_Stop_IT(&htimX); // Stop the write timer (adjust for your SDK/HAL)
    segment_count = 0;
    flag_paused = true;
  }
  

• Implement Pause Duration:
  Decide how long to pause (e.g., 1 second, or wait for an external trigger):

  • For a fixed pause: Use a second timer (or reuse the same timer in one-shot mode) to count the pause time. When it triggers:

    HAL_TIM_Base_Start_IT(&htimX); // Restart the write timer
    flag_paused = false;
    

  • For an external trigger (e.g., button press): Add a check in your main loop:

    while (flag_paused) {
      if (external_trigger_detected()) {
        HAL_TIM_Base_Start_IT(&htimX);
        flag_paused = false;
        break;
      }
      HAL_Delay(10); // Avoid busy-waiting
    }
    

• Main Loop Logic (Critical!):
  Keep your main loop focused on handling write requests and pause logic so SD operations don’t block time-sensitive tasks:

  while (1) {
    if (flag_write_segment && !flag_paused && buffer_not_empty()) {
      // Pull the next segment from your buffer
      adc_segment_t next_segment = buffer_pop();
      // Write to SD using your existing function
      sd_write_segment(&next_segment);
      // Clear the write flag
      flag_write_segment = false;
    }
  
    // Handle external trigger pause here if needed
    if (flag_paused && external_trigger_detected()) {
      HAL_TIM_Base_Start_IT(&htimX);
      flag_paused = false;
    }
  }
  

Key Notes to Avoid Issues #

• Buffer Safety: Use a thread-safe circular buffer with atomic read/write pointers—your zero-crossing code and timer interrupt will access the buffer concurrently.
• SD Latency: If SD writes take longer than 100ms, increase your buffer size or use DMA for SD operations if your MCU supports it to avoid dropping segments.
• Timer Precision: Stick to hardware timers instead of software delays—software delays drift when other tasks run.

内容的提问来源于stack exchange，提问作者joe