[embedded] print log using JLINK RTT

It can be used without serial port JLINK Of RTT namely Real Time Transfer function .RTT The working principle of is to create a in memory RTT Control block RTT Control Block, namely SEGGER_RTT_CB Structure . There are several uplink and downlink channels stored in this structure , Each channel has a data buffer And read and write pointers , Constitute a data queue . towards RTT Write... In the data queue of any uplink channel in the control block log Information , then JLINK Able to read and write RAM Content , Get the data of the queue buffer And write the contents of the pointer , And update the read pointer . If the data written is too fast ,JLINK If the refresh rate of is too late to read the contents of the queue , The queue may be full , Data loss , You can appropriately increase the length of the upload queue ：BUFFER_SIZE_UP, In profile SEGGER_RTT_Conf.h in .

stay JLINK In the installation directory of RTT Code for ：

You can use it directly SEGGER_RTT_Write Function to write a string ：

SEGGER_RTT_Write(0, "0123456789", 10);

Or use SEGGER_RTT_printf Format and print ：

SEGGER_RTT_printf(0, "%s\n", "test");

Use RTTViewer Tools can be passed through JLINK Real time reading RAM Get the data content of the upload channel ：

Due to the need to obtain chips RAM Data in , Then you have to know what to read RAM Address , That is to say RTT Control Block The address of .RTT Control Block The structure of is defined as ：

typedef struct {
  char                    acID[16];                                 // Initialized to "SEGGER RTT"
  int                     MaxNumUpBuffers;                          // Initialized to SEGGER_RTT_MAX_NUM_UP_BUFFERS (type. 2)
  int                     MaxNumDownBuffers;                        // Initialized to SEGGER_RTT_MAX_NUM_DOWN_BUFFERS (type. 2)
  SEGGER_RTT_BUFFER_UP    aUp[SEGGER_RTT_MAX_NUM_UP_BUFFERS];       // Up buffers, transferring information up from target via debug probe to host
  SEGGER_RTT_BUFFER_DOWN  aDown[SEGGER_RTT_MAX_NUM_DOWN_BUFFERS];   // Down buffers, transferring information down from host via debug probe to target
} SEGGER_RTT_CB;

The program defines a RTT Control Block Variable ：_SEGGER_RTT

SEGGER_RTT_PUT_CB_SECTION(SEGGER_RTT_CB_ALIGN(SEGGER_RTT_CB _SEGGER_RTT));

among acID Will be initialized to a fixed string value ：“SEGGER RTT”, You can use this string as Magic Number, Throughout RAM Search in the space RTT Control Block The location of , But a little silly . Find the compiled map file , lookup _SEGGER_RTT The location of ：

  And then in RTT Viewer Inside connect When setting RTT control block The address is _SEGGER_RTT The address of ：

Running results ：

RTT Viewer The terminal supports the display of different character colors and screen emptying instructions ,SEGGER_RTT.h There are control instruction definitions in , Examples of usage ：

SEGGER_RTT_Write(0, RTT_CTRL_BG_BLACK RTT_CTRL_TEXT_RED "0123456789", 20);

SEGGER_RTT_printf(0, RTT_CTRL_BG_GREEN RTT_CTRL_TEXT_YELLOW "%s\n", "test");

Running results ：

It's a little inconvenient to be in data When adding variables to the segment , The memory address of the data may change , that _SEGGER_RTT Your address will change , In this way, you should check every time _SEGGER_RTT The address of , More trouble , have access to attribute Keyword assignment _SEGGER_RTT Variables are stored in memory , Be careful to avoid the default allocation in the startup file stack Address area and heap Address area , For example, here I change it to ：

//SEGGER_RTT_PUT_CB_SECTION(SEGGER_RTT_CB_ALIGN(SEGGER_RTT_CB _SEGGER_RTT));
SEGGER_RTT_CB _SEGGER_RTT __attribute__ ((at(0x1FFE4000)));