We have an M0 here (custom mfg, but OTS IP), and need to use RTT fluidly. I've got the V5.10p software and Keil UV5 and a USB J-Link through JTAG. We are running code in RAM.

When I did the RTT Viewer and "Existing Session", I got:

0> SEGGER J-Link V5.02f - Real time terminal output
0> J-Link V10 compiled Mar 15 2016 18:03:41 V10.0, SN=50000599
0> Process: UV4.exe

But no other viewer output. This looks like text which sources from the debugger, not our cortex. That last line looks irregular- I'm using UV5, not UV4. I went with USB, "Cortex-M0", JTAG, 1MHz, RTT Control Block 0=auto, got nothing.

Inside Keil, I tried the Command window and typed _SEGGER_RTT and got 0x10000434, so I put that into "RTT Control Block" and it WORKS, my printf data comes across and anything I type ends up in the downlink buffer. But I can't ask our users to manually check the address after every compile and copy that into the config.

The manual says SEGGER_RTT_IN_RAM should be defined as (1) in certain cases. I found this in older versions of RTT code (which also didn't work automatically, with or without this defined to 1, and I called the Init task)- but it does NOT exist at all in v5.10p, even though it's still in the User Guide. There's nothing to set.

I read some ambiguous stuff that the SEGGER_RTT_IN_RAM wasn't necessary if you had the Jlink, even with the code in RAM, it could get the _SEGGER_RTT from code automatically. I did see the Keil Command window say "ws SEGGER_RTT_IN_RAM" at some point, which I thought was RTT Viewer grabbing the address without exhaustively searching RAM. But it wasn't working with or without that SEGGER_RTT_IN_RAM =1. I don't see any way to query RTT Viewer to see what address it's trying to use for the Buffer Control Block, although Channel Infos does give the buffer sizes.

The actual question: how can I get this to automatically find the RTT Control block, instead of asking Keil for _SEGGER_RTT and copying it into the Viewer config manually?

OK, so SEGGER_RTT_IN_RAM isn't a thing anymore, but what about the "SEGGER_RTT_Init()" task, is that still necessary?

I tried the RTT Viewer setup and gave a base+range for RTT and it seems to work!

What's it take to become a "known device"?

It looks like I was mistaken. In my test I already had a session connected and it used that, it did NOT find the RTT Control block.

My _SEGGER_RTT is 0x10000434. I opened the RTT Viewer, did "USB", "Cortex-M0", JTAG 4000KHz, RTT Control Block "0x10000000 0x2000"

Nothing is displayed. I checked Channel Info and I get "RTT Control Block not found on target, yet".

Shouldn't this work? An automatic RTT detection is kinda critical here.

I looked through and tried the following commands in J-Link Commander:

exec SetRTTSearchRanges 0x10000000 0x2000

Then opened RTT Viewer and left RTT Control Block at "0" for searching. It didn't work, did I not do this right?

I also tried:
exec SetRTTAddr 0x10000500

This is my known RTT address. Again, starting RTT Viewer from there doesn't make it work. What's the relationship between these JLink Commander commands and the RTT Viewer environment?

Just as a context, we need to provide demo boards to a handful of customers, and explaining "every time you compile, go to Debug Command window, type _SEGGER_RTT, then open up RTT Viewer and enter that number"... it seems sub-optimal.

I ended up going into SEGGER_RTT.c and changing (in Keil) to:

SEGGER_RTT_CB __attribute__((at(0x10000500))) _SEGGER_RTT;

This did, in fact, result in the _SEGGER_RTT assuming a fixed location. Is there a more elegant way of doing this?