embedded - 如何在Cortex-M4 MCU上捕获和查看ITM跟踪信息？

Question

我想捕获，解码和查看Cortex-M4 MCU(在我的情况下为Atmel SAM4S)的ITM跟踪信息。特别是，我想捕获异常和用户跟踪数据(相对于我板上的其他信号)(即在同一时间线上显示所有信号和跟踪信息)。

Answer 1

可以使用以下步骤完成此操作:

将调试器置于SWD模式下。如果在Linux上使用J-Link Segger，则可以使用JLinkGDBServer -if swd

完成

向MCU添加代码以启用跟踪。将比特率设置为适合您需要的值(我使用8 MHz)。示例Ada代码如下。

使用逻辑分析器从SAM4S处理器捕获TRACESWO线上的跟踪数据。我使用了100 MHz采样率的Saleae Logic Pro 16。

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 channel 进行捕获(因此每个样本导出一个字节)。

将数据以二进制格式导出到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

在PulseView中打开trace.sr文件。

将UART解码器添加到TRACESWO channel ，比特率8000000。

堆栈ARM-ITM解码器。

有关更多信息，请参见 http://www.sigrok.org/blog/new-protocol-decoders-arm-tpiu-itm-etmv3。

SAM4S跟踪的示例Ada代码:

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;