RTT waste more ram than you thought

RE: RTT waste more ram than you thought

Christopher — Tue, 19 Apr 2016 19:39:04 GMT

Yes, I can patch the files provided by Segger/Nordic, but I think this is more like a bug.

RE: RTT waste more ram than you thought

Tien — Mon, 18 Apr 2016 06:45:20 GMT

Did you remove the buf_normal_up[] and buf_down[] ? and try this config:

#define SEGGER_RTT_MAX_NUM_UP_BUFFERS             (1)     // Max. number of up-buffers (T->H) available on this target    (Default: 2)
#define SEGGER_RTT_MAX_NUM_DOWN_BUFFERS           (1)     // Max. number of down-buffers (H->T) available on this target  (Default: 2)

#define BUFFER_SIZE_UP                            (64)   // Size of the buffer for terminal output of target, up to host (Default: 1k)
#define BUFFER_SIZE_DOWN                          (1)    // Size of the buffer for terminal input to target from host (Usually keyboard input) (Default: 16)

RE: RTT waste more ram than you thought

Christopher — Mon, 18 Apr 2016 06:25:58 GMT

Hi,

I also use RTT in my application, running on an nRF51 chip with 16k RAM. I use RTT only to send trace messages to a PC client (SEGGER_RTT_BUFFER_UP) and I do not need the SEGGER_RTT_BUFFER_DOWN buffer at all.

In the latest RTT implementation given by Segger (RTT version 5.12b), the buffer are declared 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;

Depending on the compiler, it is not allowed to declare an array with a length of '0'. Is there a Nordic implementation of RTT which allow to disable the down buffer ? I have a limited amount of RAM and I do not like to lost bytes for a buffer I do no use.