6.3.2 Host to Target
Host to target communication utilizes SEGGER's Real Time Transfer (RTT) technology. A full explanation of how this works can be
found in
J-Link/J-Trace User Guide (UM08001)
. Briefly summarized, RTT consists of a structure called the RTT Control Block, which is
located in RAM. This control block points to circular buffers that the debugger can write data into. The target application can then read
data out of this circular buffer.
The board controller will start searching for the RTT Control Block upon receiving data on TCP/IP port 4900. If the board controller is
unable to locate the RTT Control Block, it will return an error message on the same connection. For the board controller to be able to
locate the RTT Control Block, it has to be aligned on a 1024-byte boundary in RAM.
After initializing the RTT connection, the target will only enter emulated EM2 and EM3 where the power consumption remains similar to
EM1. This is because RTT utilizes the debug interface which requires use of high-frequency oscillators. Energy modes EM4S and
EM4H will work as normal. When debugging energy consumption, it is therefore important to not send data on TCP/IP port 4900 as not
to instantiate the RTT connection.
6.3.3 Limitations
• Because the SWO-connection can be disabled by the debugger at will, it is important for the target application to verify that SWO is
enabled and configured before each transmission on the interface.
• After initializing host to target communication over RTT by sending data on TCP/IP port 4900, the target application will be unable to
enter EM2 and EM3. This is because RTT utilizes the debug connection of the target.
• VUART might not work reliably during an active debugging session. This is because there is contention over the target's debug inter-
face. The board controller will defer accessing the target until it is made available by the host debugger.
• VUART is designed with the assumption that only the board controller will access the RTT control block. If the target application
uses RTT for other purposes, such as Segger SystemView, refrain from using VUART.
6.3.4 Troubleshooting
Problem
Solution
No data received after ending a
debug session.
After certain debugger operations, the host computer manually disables SWO on the target in order
to conserve power. This might cause SWO data to not appear if the target application initialized
SWO before the debugger has disconnected. Either press the RESET-button on the Wireless Start-
er Kit to reset the target application or make sure that the target application verifies that SWO is en-
abled and configured before sending any data.
No data received after flashing
a new application.
Other issues
Disconnect from TCP port 4900, press the RESET-button on the kit, then reconnect to 4900. If this
does not fix the issue, try to restart the kit by unplugging and replugging the USB cable.
UG525: EFR32xG24 2.4 GHz 10 dBm Wireless Pro Kit User's Guide
Board Controller
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