串口收发性能测试

本页测试 LibXR 串口驱动在 2～9 Mbaud 下的收发速率，以及收发过程中的线程调度情况。数据为早期测试记录，只对应下文列出的 STM32F103C8、CH32V307VC 和 STM32F407IG；下文的测试代码已按当前 LibXR 更新，数据没有重新测量。

测试环境

串口驱动是整个LibXR里面最复杂的部分，性能测试的环境如下：

STM32F103C8，Cortex-M3 @ 72 MHz
CH32V307VC, RISC-V @ 144 MHz
STM32F407IG，Cortex-M4 @ 168 MHz
Debug模式只有用户代码是-Og优化，HAL库，FreeRTOS，USB等库是-O2优化。Release模式都为-O3优化。
使用杜邦线将USART1的TX RX连接起来，数据位为8，停止位为1，无流控，无奇偶校验
收到数据后对整包进行CRC校验，每秒统计发送成功、发送失败和总共校验失败的次数

测试代码

同步方式收发各使用一个线程，虽然上下文切换会带来一些性能损失，但是影响不大。追求极限性能可以使用异步方式收发。

  constexpr size_t BUFFER_SIZE = 32;
  constexpr size_t BAUDRATE = 2000000;

  static uint8_t read_buffer[BUFFER_SIZE], write_buffer[BUFFER_SIZE];
  static uint32_t count_read = 0, count_write = 0, count_error = 0;

  for (uint32_t i = 0; i < sizeof(write_buffer); i++) {
    write_buffer[i] = i;
  }

  STDIO::write_ = uart_cdc.write_port_;

  void (*fun)(void *) = [](void *) {
    LibXR::STDIO::Printf<"read count: %u, write count: %u, error count: %u\r\n">(
        count_read, count_write, count_error);
    LibXR::STDIO::Printf<"speed: %u BAUD\r\n">(
        static_cast<unsigned>(count_read * 10 * sizeof(write_buffer)));
    count_read = 0;
    count_write = 0;
  };

  auto print_task =
      LibXR::Timer::CreateTask(fun, reinterpret_cast<void *>(0), 1000);
  LibXR::Timer::Add(print_task);
  LibXR::Timer::Start(print_task);

  void (*thread_read)(LibXR::UART *) = [](LibXR::UART *uart) {
    LibXR::Semaphore sem(0);
    LibXR::ReadOperation op(sem);
    while (true) {
      uart->Read(read_buffer, op);
      if (LibXR::CRC8::Verify(read_buffer, sizeof(read_buffer))) {
        count_read++;
      } else {
        count_error++;
      }
    }
  };

  void (*thread_write)(LibXR::UART *) = [](LibXR::UART *uart) {
    LibXR::Semaphore sem(0);
    LibXR::WriteOperation op(sem);

    uart->SetConfig({BAUDRATE, LibXR::UART::Parity::NO_PARITY, 8, 1});

    while (true) {
      write_buffer[0]++;
      write_buffer[sizeof(write_buffer) - 1] = LibXR::CRC8::Calculate(
          write_buffer, sizeof(write_buffer) - sizeof(uint8_t));

      uart->Write(write_buffer, op);
      count_write++;
    }
  };

  LibXR::Thread read_thread, write_thread;

  read_thread.Create(reinterpret_cast<LibXR::UART *>(&usart1), thread_read,
                     "read_thread", 2048,
                     static_cast<LibXR::Thread::Priority>(4));

  write_thread.Create(reinterpret_cast<LibXR::UART *>(&usart1), thread_write,
                      "write_thread", 2048,
                      static_cast<LibXR::Thread::Priority>(3));

  while (true) {
    LibXR::Thread::Sleep(UINT32_MAX);
  }

代码块已折叠

速率测试

STM32F1 -Og 32字节 2M波特率

32字节接近实际的串口数据包大小，在2M波特率下能够逼近串口理论速率。

read count: 6000, write count: 5999, error count: 0
speed: 1920000 BAUD
read count: 6000, write count: 6000, error count: 0
speed: 1920000 BAUD
read count: 5999, write count: 6000, error count: 0
speed: 1919680 BAUD
read count: 6000, write count: 5999, error count: 0
speed: 1920000 BAUD
read count: 6000, write count: 6000, error count: 0
speed: 1920000 BAUD
read count: 5999, write count: 6000, error count: 0
speed: 1919680 BAUD

STM32F1 -O3 32字节 2M波特率

O3优化下没有明显区别

read count: 6000, write count: 5999, error count: 0
speed: 1920000 BAUD
read count: 5999, write count: 6000, error count: 0
speed: 1919680 BAUD
read count: 6000, write count: 6000, error count: 0
speed: 1920000 BAUD
read count: 6000, write count: 5999, error count: 0
speed: 1920000 BAUD
read count: 5999, write count: 6000, error count: 0
speed: 1919680 BAUD
read count: 6000, write count: 6000, error count: 0
speed: 1920000 BAUD

STM32F1 -Og 128字节 4M波特率

更大的数据包，更高的波特率

read count: 3061, write count: 3061, error count: 0
speed: 3918080 BAUD
read count: 3062, write count: 3062, error count: 0
speed: 3919360 BAUD
read count: 3062, write count: 3062, error count: 0
speed: 3919360 BAUD
read count: 3061, write count: 3061, error count: 0
speed: 3918080 BAUD
read count: 3062, write count: 3062, error count: 0
speed: 3919360 BAUD
read count: 3063, write count: 3062, error count: 0
speed: 3920640 BAUD

CH32V307 -Og 64字节 9M波特率

9M波特率下一样能够达到理论速率

read count: 14000, write count: 14000, error count: 0
speed: 8960000 BAUD
read count: 14000, write count: 14000, error count: 0
speed: 8960000 BAUD
read count: 14000, write count: 14000, error count: 0
speed: 8960000 BAUD
read count: 14000, write count: 14000, error count: 0
speed: 8960000 BAUD
read count: 14000, write count: 14000, error count: 0
speed: 8960000 BAUD
read count: 14000, write count: 14000, error count: 0
speed: 8960000 BAUD

系统调用分析

以下使用 STM32F4 与 SystemView 展示收发过程中的系统调用。系统调用只有线程唤醒和同步所需的信号量操作。

较低波特率

低波特率下多个包被连起来，无法触发IDLE中断。写线程周期性被唤醒，读线程等到半满/全满中断时被唤醒。

Low Speed

较高波特率

高波特率下，一收一发两个线程轮流唤醒。

High Speed

总结

在 STM32F103（72 MHz）上，32 字节包 2 Mbaud 与 128 字节包 4 Mbaud 的测试中，线路速率接近设定波特率，CRC 校验无错误；CH32V307（144 MHz）在 9 Mbaud 下同样接近设定波特率。

测试环境​

测试代码​

速率测试​

STM32F1 -Og 32字节 2M波特率​

STM32F1 -O3 32字节 2M波特率​

STM32F1 -Og 128字节 4M波特率​

CH32V307 -Og 64字节 9M波特率​

系统调用分析​

较低波特率​

较高波特率​

总结​