如何捕获和查看 Cortex-M4 MCU 上的 ITM 跟踪信息？

我想捕获、解码和查看 Cortex-M4 MCU（在我的例子中是 Atmel SAM4S）的 ITM 跟踪信息。特别是，我想捕获与板上其他信号相关的异常和用户跟踪数据（即在同一时间线上显示所有信号和跟踪信息）。

这可以通过以下步骤完成：

1. 将调试器置于 SWD 模式。如果在 Linux 上使用 J-Link Segger，可以使用以下命令完成JLinkGDBServer -if swd
2. 将代码添加到 MCU 以启用跟踪。将比特率设置为适合您需要的值（我使用 8 MHz）。 Ada 代码示例如下。
3. 使用逻辑分析仪从 SAM4S 处理器捕获 TRACESWO 线上的跟踪数据。我使用了具有 100 MHz 采样率的 Saleae Logic Pro 16。

4. 将数据转换为 sigrok 可用的格式。使用Saleae捕获数据，包括以下步骤：

   • 仅使用前 8 个通道进行捕获（因此每个样本导出一个字节）。
   • 将数据导出为二进制trace.bin，为每个样本写入一个字节。

   • 使用以下命令转换为trace.sr 文件：

     sigrok-cli -i trace.bin -I binary:samplerate=100000000,numchannels=4 -o trace.sr

5. 打开trace.srPulseView 中的文件。
6. TRACESWO通道添加UART解码器，比特率8000000。
7. 堆栈 ARM-ITM 解码器。

See http://www.sigrok.org/blog/new-protocol-decoders-arm-tpiu-itm-etmv3 http://www.sigrok.org/blog/new-protocol-decoders-arm-tpiu-itm-etmv3了解更多信息。

SAM4S Trace 的 Ada 代码示例：

sam4s-trace.ads：

with Interfaces;

package SAM4S.Trace is
   pragma Preelaborate;

   type Channel_Type is new Integer range 0 .. 31;
   type Value_Type is new Interfaces.Unsigned_32;

   procedure Initialize;

   procedure Put (Channel : Channel_Type;
                  Value   : Value_Type);

   procedure Put (Channel : Channel_Type;
                  Message : String);
end SAM4S.Trace;

sam4s-trace.adb：

with System;
with System.Storage_Elements; use System.Storage_Elements;

package body SAM4S.Trace is
   procedure Initialize is
      ITM_LAR : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E000_0FB0#), Volatile;

      ITM_TCR : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E000_0E80#), Volatile;

      ITM_TER : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E000_0E00#), Volatile;

      ITM_TPR : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E000_0E40#), Volatile;

      DEMR : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E000_EDFC#), Volatile;

      TPIU_SPP : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E004_00F0#), Volatile;

      TPIU_FFCR : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E004_0304#), Volatile;

      TPIU_ACPR : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E004_0010#), Volatile;

      DWT_CTRL : Interfaces.Unsigned_32
        with Address => System'To_Address (16#E000_1000#), Volatile;

      use Interfaces;

   begin
      --  Enable write access via the Lock Access Register.
      ITM_LAR := 16#C5AC_CE55#;
      --  Enable the ITM, enable SWO mode behavior, enable synchronization
      --  packets, enable DWT event submission, enable timestamps.
      ITM_TCR := 16#0001_001F#;
      --  Enable access in user mode to all 32 channels.
      ITM_TPR := 16#0000_0000#;
      --  Enable all 32 trace channels.
      ITM_TER := 16#FFFF_FFFF#;

      --  Set TRCENA bit to 1 in Debug Exception and Monitor Register.
      DEMR := DEMR or 16#0100_0000#;

      --  Select NRZ serial wire output.
      TPIU_SPP := 16#0000_0002#;

      --  Deactivate formatter.
      TPIU_FFCR := 16#0000_0100#;

      --  Set prescalar (/10).
      --  TPIU_ACPR := 16#0000_0009#;

      --  Set prescalar (/15).
      TPIU_ACPR := 14;

      --  Enable exception trace and exception overhead.
      DWT_CTRL := DWT_CTRL or 16#0005_0000#;

   end Initialize;

   procedure Put (Channel : Channel_Type;
                  Value   : Value_Type) is
      Port_Reg : Value_Type with Address => System'To_Address (16#E000_0000#) +
        4 * Channel_Type'Pos (Channel), Volatile;
   begin
      --  Port register lsb is set when the the FIFO can accept at least one
      --  word.
      while Port_Reg = 0 loop
         null;
      end loop;
      Port_Reg := Value;
   end Put;

   procedure Put (Channel : Channel_Type;
                  Message : String) is
      Port_Reg : Value_Type with Address => System'To_Address (16#E000_0000#) +
        4 * Channel_Type'Pos (Channel), Volatile;
   begin
      --  Port register lsb is set when the the FIFO can accept at least one
      --  word.
      for Index in Message'Range loop
         while Port_Reg = 0 loop
            null;
         end loop;
         Port_Reg := Value_Type (Character'Pos (Message (Index)));
      end loop;
   end Put;

end SAM4S.Trace;