树莓派4使用Python spidev与MCP3008时出现Segmentation fault错误

你的代码存在几个关键错误，这些是导致段错误和无法启动的核心原因，以下是逐一修正方案：

1. 修复SPI传输函数调用错误 #

spidev.SpiDev.xfer()的参数应为字节列表，而非三个独立整数。MCP3008的正确读取逻辑是发送包含3个字节的指令：

• 第一个字节：1（起始位）
• 第二个字节：(8 + 通道号) << 4（通道选择，比如通道0对应128、通道3对应176）
• 第三个字节：0（填充位，用于接收数据）

错误写法：

answerV = spi.xfer(1,128,0)
answerC = spi.xfer(1,176,0)

正确写法：

answerV = spi.xfer([1, 128, 0])
answerC = spi.xfer([1, 176, 0])

2. 修复函数缩进错误 #

get_voltage()中的return voltage_measurement缩进错误（位于函数外部），会触发语法错误，需缩进至函数内部：

修正后：

def get_voltage():
    answerV = spi.xfer([1, 128, 0])
    if 0 <= answerV[1] <= 3:
        voltage_measurement = ((((answerV[1] * 256) + answerV[2]) * 0.00322) * 90) // 40
        print(voltage_measurement, " V")
    return voltage_measurement

3. 修复变量未定义问题 #

• get_current()中，若第一个if条件不满足，current_measurement会未定义就返回，需提前初始化默认值：

def get_current():
    current_measurement = 0  # 初始化默认值
    answerC = spi.xfer([1, 176, 0])
    if 0 <= answerC[1] <= 3:
        current_measurement = ((answerC[1] * 256) + answerC[2]) * 0.00322 * 0.066
        print(current_measurement, " A")
    if ((answerC[1] * 256) + answerC[2]) * 0.00322 == 2:
        current_measurement = 0
    return current_measurement

• 主循环中p变量未定义，需先调用get_power()计算功率：

while True:
    tm = get_time()
    i = get_current()
    v = get_voltage()
    p = get_power(v, i)  # 新增该行
    writer.writerow([tm, v, i, p])
    time.sleep(1)

4. 优化文件写入逻辑 #

直接open("data.csv", "w")可能导致数据缓冲无法及时写入，建议用with语句管理文件，确保正确打开/关闭，同时手动触发刷新：

# 替换原writer初始化及主循环代码
with open("data.csv", "w", newline='') as f:
    writer = csv.writer(f)
    writer.writerow(["time", "voltage", "current", "power"])
    
    while True:
        tm = get_time()
        i = get_current()
        v = get_voltage()
        p = get_power(v, i)
        writer.writerow([tm, v, i, p])
        f.flush()  # 确保数据立即写入文件
        time.sleep(1)

5. 调整SPI速度（可选） #

MCP3008支持最高1MHz的SPI速度，原代码5000Hz过低，可调整为更合理的值：

spi.max_speed_hz = 100000  # 100kHz，兼顾稳定性和速度

完整修正后的代码 #

import spidev
import time
import csv
import datetime as dt

spi = spidev.SpiDev()
spi.open(0, 1)
spi.max_speed_hz = 100000

def get_time():
    tm = dt.datetime.now().strftime("%d.%m.%Y-%H:%M")
    return tm

def get_voltage():
    voltage_measurement = 0
    answerV = spi.xfer([1, 128, 0])
    if 0 <= answerV[1] <= 3:
        voltage_measurement = ((((answerV[1] * 256) + answerV[2]) * 0.00322) * 90) // 40
        print(voltage_measurement, " V")
    return voltage_measurement

def get_current():
    current_measurement = 0
    answerC = spi.xfer([1, 176, 0])
    if 0 <= answerC[1] <= 3:
        current_measurement = ((answerC[1] * 256) + answerC[2]) * 0.00322 * 0.066
        print(current_measurement, " A")
    # 替换浮点数精确比较，改用范围判断避免精度问题
    raw_voltage = ((answerC[1] * 256) + answerC[2]) * 0.00322
    if abs(raw_voltage - 2) < 0.01:
        current_measurement = 0
    return current_measurement

def get_power(v, i):
    return v * i

with open("data.csv", "w", newline='') as f:
    writer = csv.writer(f)
    writer.writerow(["time", "voltage", "current", "power"])
    
    while True:
        tm = get_time()
        i = get_current()
        v = get_voltage()
        p = get_power(v, i)
        writer.writerow([tm, v, i, p])
        f.flush()
        time.sleep(1)

注：原代码中浮点数==2的判断可能因精度问题失效，改用范围判断更可靠。

内容的提问来源于stack exchange，提问作者moknavi