Poll for BOOTSEL readiness instead of fixed sleep, load with -x

cmd/load/main.go

@@ -116,7 +116,19 @@ func run(buildDir string) error {
 		}
 	}
 
-	time.Sleep(2 * time.Second)
+	for i := range 2 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			errs[i] = picotool.WaitForBootsel(serials[i], 10*time.Second)
+		}()
+	}
+	wg.Wait()
+	for i, err := range errs {
+		if err != nil {
+			return fmt.Errorf("wait %s: %w", serials[i], err)
+		}
+	}
 
 	uf2s := []string{
 		filepath.Join(buildDir, "picomap.uf2"),
@@ -138,21 +150,6 @@ func run(buildDir string) error {
 		}
 	}
 
-	fmt.Println("Rebooting...")
-	for i := range 2 {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			errs[i] = picotool.Reboot(serials[i])
-		}()
-	}
-	wg.Wait()
-	for i, err := range errs {
-		if err != nil {
-			return fmt.Errorf("reboot %s: %w", serials[i], err)
-		}
-	}
-
 	fmt.Println("Done.")
 	return nil
 }