problems with multiple channels

[tpilt]

Hi,

I'm having problems with getting from channel 1,2,3 printed on the host side. Channel 0 works fine, and downlink channel 0 also works fine.

#[entry]
fn main() -> ! {
    let channels = rtt_init! {
        up: {
            0: {
                size: 1024
                name: "Trace"
            }
            1: {
                size: 1024
                name: "Shell up"
            }
        }
    };
    let mut shell_up = channels.up.1;
    let mut trace_up = channels.up.0;

    trace_up.write(b"trace_up\n"); // works fine
    shell_up.write(b"shell_up\n"); // does NOT work!

    set_print_channel(trace_up); // works fine
    rprintln!("main() says hello...");  // works fine

    loop {}
}

This does not print "shell_up" as expected. Is it a blunder on my side? :-)

[mvirkkunen]

What command are you using to view the output?

[tpilt]

###RTT Client: Connected.

SEGGER J-Link V6.70c - Real time terminal output
SEGGER J-Link ARM V10.0, SN=600001020
Process: JLinkGDBServerCLExe
trace_up
main() says hello...

Also tried the Gui version. (I'm on linux)

I tried singlestepping a bit into the write-call, and I got quite deep, I think it wrote something to some buffer... then I gave up.

How do we debug this? Should I try to NOT have the client connected. Then I can hex-dump the entire RTT memory before and after the call. (I'll need help for the hex-dumping :-) )

Or should we caputre the USB communication?

[mvirkkunen]

I haven't used that particular client because I don't have a J-Link and I assume it only works with those. Does it have command line options to specify which channels to use? Is it possible that by default it only looks at channel 0?

[mvirkkunen]

While I can't test this, these posts would suggest that the official viewer only supports channel 0 (Terminal):

https://forum.segger.com/index.php/Thread/2030-RTT-multiple-channels/

https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/multiple-channels-in-rtt

Apparently you're supposed to use "RTT Logger" instead if you want to view multiple channels.

You could also use cargo embed, which has a multi-channel viewer implemented with an RTT host library I also wrote and is known to work - although if you can spare the time, I'd be glad if you could also test with Segger's logger software just to verify.

[tpilt]

Thx, turns out that there is a difference between 'channels', and 'terminals', in Seggers terminology, that I was unaware of.

As written I also tried 'the GUI version', which is this: https://www.segger.com/products/debug-probes/j-link/tools/rtt-viewer/ This has different tabs , I assumed them to be 'channels' , but they are 'terminals'.

Looks like they send some kind of escape sequence, to set a new 'terminal' (0xFF 0x02 for terminal 2, if I'm not mistaken) and then send the string/data on CHANNEL 0. https://github.com/contiki-os/contiki/blob/master/platform/nrf52dk/rtt/segger-rtt.c

Regarding JLinkRTTLogger, you're (also!) right:

Searching for RTT Control Block...OK. 2 up-channels found.
RTT Channel description: 
  Index: 1
  Name:  Shell up
  Size:  1024 bytes.

Output file: /home/xxx/.config/SEGGER\RTTLogger_Channel_Shell up.log

( notice the backslash in the filename ... I think this was intended to go into a subdir, and indeed it will on windows :-) )

I must choose which channel to log from, but on linux at least, I can successfully have the VSCode debugging the application, and run two JLinkRTTLogger at the same time, logging to two different files.

I think I will look into the "cargo embed" crate soon. Just for fun, I might also try to send the "\xFF\x2" sequence, and see, if the JLinkRTTViewer now pick it up as 'terminal' 2.

[mvirkkunen]

rtt-target also supports the escape sequences for the different virtual terminals! It also takes care of not sending it partially if the buffer is almost full.

If using rprintln! there's a special syntax for it: https://docs.rs/rtt-target/0.1.1/rtt_target/macro.rprintln.html

If not, you can create a TerminalChannel: https://docs.rs/rtt-target/0.1.1/rtt_target/struct.TerminalChannel.html

[tpilt]

Indeed, this makes JLinkRTTViewer write into different 'terminals':

        let ch0: [u8; 2] = [0xFF, b'0'];
        let ch1: [u8; 2] = [0xFF, b'1'];
        // toggle alive-leds
        if second_elapsed {
            if uptime & 0x01 == 0 {
                efm_per.GPIO.pa_dout.write(|w| unsafe { w.bits(0x55) });
                trace_up.write(&ch0);
                trace_up.write(b"hoping for this to arrive at terminal 0\n");
            } else {
                trace_up.write(&ch1);
                trace_up.write(b"hoping for this to arrive at terminal 1\n");
                efm_per.GPIO.pa_dout.write(|w| unsafe { w.bits(0xAA) });
            }
        }

"All Terminals" Tab:

00> hoping for this to arrive at terminal 0
01> hoping for this to arrive at terminal 1
00> hoping for this to arrive at terminal 0
01> hoping for this to arrive at terminal 1
00> hoping for this to arrive at terminal 0
01> hoping for this to arrive at terminal 1
00> hoping for this to arrive at terminal 0

"Terminal 0" Tab

hoping for this to arrive at terminal 0
hoping for this to arrive at terminal 0
hoping for this to arrive at terminal 0
...

"Terminal 1" Tab

hoping for this to arrive at terminal 1
hoping for this to arrive at terminal 1
hoping for this to arrive at terminal 1
...

[tpilt]

Argh, these post crossed.... I WAS looking at the ( => 2, "hello") syntax at one time. But had trouble working all this out. Thx for all help :-)

[mvirkkunen]

Maybe it'd be a good idea to document what channels and terminals mean in the library docs because it can be confusing if you don't already know.