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Date of registration: Jan 20th 2016

Posts: 21


Thursday, October 5th 2017, 5:25pm

[SOLVED] Again - or still: Failed to start recording. RTT Control Block not found.

I read through many posts but still I do not get it working. The control block address is
0x200021e8 (retrieved via _SEGGER_RTT in Keil command window).

However, I do not receive RTT with SystemView.

J-Link commander does not give an output when I type, e.g.:
J-Link> exec SetRTTSearchRanges 0x20002000 0x1000

J-Link RTT Client shows:
###RTT Client: Connecting to J-Link RTT Server via localhost:19021 Connected.
SEGGER J-Link V6.20d - Real time terminal output
J-Trace PRO V1 Cortex-M compiled Sep 26 2017 17:01:49 V1.0, SN=751000184
Process: UV4.exe

This is my environment:
Firmware: J-Trace PRO V1 Cortex-M compiled Sep 26 2017 17:01:49 Hardware: V1.00
Keil ┬ÁVision 5.22 and Segger SystemView V2.52a

Thanks for any help -


SEGGER - Johannes

Super Moderator

Date of registration: Aug 31st 2012

Posts: 379


Monday, October 9th 2017, 1:14pm

Hi Marcus,

In general there should not be a problem, as with STM32F4 devices even auto detection should work.
So if the control block cannot be found there seems to be an issue with your setup.

It is correct that J-Link Commander does not give an output, neither will RTT Client if you do not do any prontf output viar RTT.

Do you run SystemView stand-alone or is there any other connection to J-Link, e.g. a debug session, open?
Did you select the device in the SystemView configuration dialog?
Does your system use any low-power mode, i.e. call WFI?




Date of registration: Jan 20th 2016

Posts: 21


Tuesday, October 10th 2017, 11:10am

Hi Johannes,

thanks for the hint with the printf output:

SEGGER_RTT_WriteString(0, "Hello

is working correctly. Then I re-examined my code and found that the initialization block


was beyond a break statement - sorry, dumb fault. After correction everything is fine...

Thanks again,