Emit RTT logs to a file.

Then defmt-print can read them.

.gitignore

@@ -1,6 +1,6 @@
 target/
 book/
 Cargo.lock
-
+rtt.log
 .vscode/
 *.DS_Store

beginner/apps/.vscode/launch.json

@@ -18,16 +18,21 @@
           "transport select swd",
           "source [find target/nrf52.cfg]"
         ],
-        // commands only supported in OpenOCD 0.11.0; also due to how the `rtt-target` crate works
-        // these commands need to run _after_ the target executes the `rtt_init` macro so running
-        // these commands when the device is halted on `main` will fail
-        // "postLaunchCommands": [
-        //   // FIXME(?) to work with a newer version (>0.3.7) of the cortex-debug extension the
-        //   // escaped backslashes (`\\`) may need to be removed
-        //   "monitor rtt setup 0x20000000 262144 \\\"SEGGER RTT\\\"",
-        //   "monitor rtt start",
-        //   "monitor rtt server start 8765 0",
-        // ],
+        "rttConfig": {
+          "enabled": true,
+          "address": "auto",
+          "decoders": [
+            {
+              "port": 0,
+              "type": "console",
+              "label": "Defmt RTT",
+              // You can parse this log file with
+              // tail -F rtt.log | defmt-print -e ./target/thumbv7em-none-eabihf/debug/led
+              "logfile": "${workspaceRoot}/rtt.log",
+              "noprompt": true
+            }
+          ]
+        }
       }
     ]
 }