Delay JLink server startup to allow it to settle

src/common.ts

@@ -267,7 +267,7 @@ export interface GDBServerController extends EventEmitter {
     serverArguments(): string[];
     initMatch(): RegExp;
     serverLaunchStarted(): void;
-    serverLaunchCompleted(): void;
+    serverLaunchCompleted(): Promise<void> | void;
     debuggerLaunchStarted(): void;
     debuggerLaunchCompleted(): void;
 }

src/gdb.ts

@@ -398,14 +398,13 @@ export class GDBDebugSession extends DebugSession {
             }, GDBServer.SERVER_TIMEOUT);
 
             this.serverController.serverLaunchStarted();
-            this.server.init().then((started) => {
+            this.server.init().then(async (started) => {
                 if (timeout) {
                     clearTimeout(timeout);
                     timeout = null;
                 }
 
-                this.serverController.serverLaunchCompleted();
-
+                await this.serverController.serverLaunchCompleted();
                 let gdbargs = ['-q', '--interpreter=mi2'];
                 gdbargs = gdbargs.concat(this.args.debuggerArgs || []);
 

src/jlink.ts

@@ -186,7 +186,7 @@ export class JLinkServerController extends EventEmitter implements GDBServerCont
     }
 
     public serverLaunchStarted(): void {}
-    public serverLaunchCompleted(): void {
+    public serverLaunchCompleted(): Promise<void> {
         if (this.args.swoConfig.enabled) {
             if ((this.args.swoConfig.source === 'probe') || (this.args.swoConfig.source === 'socket')) {
                 const swoPortNm = createPortName(this.args.targetProcessor, 'swoPort');
@@ -200,6 +200,18 @@ export class JLinkServerController extends EventEmitter implements GDBServerCont
                 }));
             }
         }
+
+        /* The JLink Server will output its initMatch line before it's actually ready to
+         * process commands from a GDB client. This causes the JLink server's state to fall out of
+         * sync with the debugger chip from the beginning, and the GDB client will fail to start
+         * the processor correctly. This typically surfaces as a "Failed to start CPU" line in
+         * the Adapter output and all registers read as 0xdeadbeee or 0xdeadbeef until the debugger
+         * chip is reset with "monitor reset".
+         *
+         * Sleep for 500ms at the end of the server launch to give the JLink server time to
+         * settle:
+         */
+        return new Promise(resolve => setTimeout(resolve, 500));
     }
     public debuggerLaunchStarted(): void {}
     public debuggerLaunchCompleted(): void {