ATmega 328p 的静态函数表现很奇怪

发布于 2024-12-05 12:20:24 字数 1480 浏览 1 评论 0原文

我正在尝试使用 ATmega 328p（Arduino 以太网）来控制 Wiznet W5100 以太网控制器。我正在使用的库已经过测试并且可以工作，但对我来说却不行。以下是我跟踪问题的原因：

我正在尝试读取两个寄存器，它们告诉我 W5100 已接收到多少字节的数据：

uint16_t readTest() 
{
    uint16_t res = W5100.read(0x0426);
    res = (res << 8) + W5100.read(0x0427);
    return res;                                             
}

但是即使我没有发送任何数据，该函数还是从 main 调用的()，将返回 1024 而不是 0。现在奇怪的部分来了：如果我像这样添加 static 关键字：

static uint16_t readTest() 
{
    uint16_t res = W5100.read(0x0426);
    res = (res << 8) + W5100.read(0x0427);
    return res;                                             
}

那么该函数会突然返回 0，正如它应该的那样！我也可以将其更改为：

uint16_t readTest() 
{
    return (W5100.read(0x0426) << 8) + W5100.read(0x0427);
}

这一定是编译器在搞乱我。我真的不明白。为了进行编译，我使用标准 Arduino IDE，命令如下所示：

avr-g++ -c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=22 -I/usr/share/arduino/hardware/arduino/cores/arduino -I/usr/share/arduino/libraries/SoftwareSerial -I/home/xc317/sketchbook/libraries/serlcd -I/usr/share/arduino/libraries/SPI -I/usr/share/arduino/libraries/Ethernet -I/usr/share/arduino/libraries/Ethernet/utility /usr/share/arduino/libraries/Ethernet/Server.cpp -o/tmp/build1305752250561284982.tmp/Ethernet/Server.cpp.o

此行为的原因是什么？

原文

I'm trying to use an ATmega 328p (Arduino Ethernet) to control a Wiznet W5100 Ethernet controller. The libraries I'm using are tested and work, but for me they don't. Here's what I tracked the problem down to:

I'm trying to read two registers, that tell me how many bytes of data have been received by the W5100:

uint16_t readTest() 
{
    uint16_t res = W5100.read(0x0426);
    res = (res << 8) + W5100.read(0x0427);
    return res;                                             
}

But even though I'm not sending any data, this function, called from main(), will return 1024 instead of 0. Now comes the weird part: If I add the static keyword like this:

static uint16_t readTest() 
{
    uint16_t res = W5100.read(0x0426);
    res = (res << 8) + W5100.read(0x0427);
    return res;                                             
}

Then the function suddently returns 0 as it is supposed to!
Also I could change it to this:

uint16_t readTest() 
{
    return (W5100.read(0x0426) << 8) + W5100.read(0x0427);
}

This must be the compiler messing with me. I really don't get it. To compile I use the standard Arduino IDE, the command looks something like this:

avr-g++ -c -g -Os -w -fno-exceptions -ffunction-sections -fdata-sections -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=22 -I/usr/share/arduino/hardware/arduino/cores/arduino -I/usr/share/arduino/libraries/SoftwareSerial -I/home/xc317/sketchbook/libraries/serlcd -I/usr/share/arduino/libraries/SPI -I/usr/share/arduino/libraries/Ethernet -I/usr/share/arduino/libraries/Ethernet/utility /usr/share/arduino/libraries/Ethernet/Server.cpp -o/tmp/build1305752250561284982.tmp/Ethernet/Server.cpp.o

What is the reason for this behaviour?

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