tested and updated BLE tutorial

TUTORIAL.md

@@ -520,7 +520,7 @@ Connect the badge to a computer. The joystick moves the mouse cursor; button A i
 
 ## BLE
 
-The nice!nano's nRF52840 chip has built-in Bluetooth Low Energy. These examples use the [`github.com/tinygo-org/bluetooth`](https://github.com/tinygo-org/bluetooth) library.
+The nice!nano's nRF52840 chip has built-in Bluetooth Low Energy. These examples use the [`tinygo.org/x/bluetooth`](https://tinygo.org/x/bluetooth) library.
 
 **Recommended mobile apps**
 
@@ -558,28 +558,50 @@ This example implements the **Nordic UART Service (NUS)** — a de-facto standar
 | RX | `6E400002-…` | Write, WriteWithoutResponse | Central → Badge |
 | TX | `6E400003-…` | Notify, Read | Badge → Central |
 
-The counter increments every second. `txChar.Write()` sends a notification to any subscribed central. If `Write` returns an error no device is listening — that is how connection state is tracked.
+Connection state is tracked via `adapter.SetConnectHandler`, which receives real events from the nRF52840 SoftDevice. The handler only sets flags — display and advertising calls happen in the main loop to avoid re-entering the SoftDevice from its own event callback.
 
 ```go
-_, err := txChar.Write([]byte(strconv.Itoa(counter) + "\n"))
+adapter.SetConnectHandler(func(device bluetooth.Device, c bool) {
-connected = err == nil
+    connected = c
+    connChanged = true
+})
+
+for {
+    if connChanged {
+        connChanged = false
+        if connected {
+            drawStatus("Connected   ")
+        } else {
+            drawStatus("Advertising...")
+            adv.Start()
+        }
+    }
+    counter++
+    drawCounter(counter)
+    if connected {
+        txChar.Write([]byte(strconv.Itoa(counter) + "\n"))
+    }
+    time.Sleep(time.Second)
+}
 ```
 
+`AddService` must be called before `adv.Start()` — the nRF52840 SoftDevice needs the complete GATT table before advertising begins.
+
 ```sh
 tinygo flash -target nicenano ./ble/step1
 ```
 
 **How to test**
 1. Flash the badge. The display shows `BLE: Advertising...`.
-2. Open **nRF Toolbox** → UART → Connect → search for `NiceBadge`.
+2. Open **nRF Connect** → SCANNER → search for `NiceBadge`.
 3. Once connected the display shows `BLE: Connected` and the counter appears in the terminal.
 4. Type `reset` and send it — the counter resets to zero.
 
 **Key concepts**
 - `adapter.Enable()` — starts the BLE stack (SoftDevice on nRF52840). Must be called before anything else.
-- `adapter.AddService` — registers the GATT service and its characteristics.
+- `adapter.AddService` must be called **before** `adv.Start()` on nRF52840 — the GATT table is frozen once advertising starts.
-- `adv.Start()` — begins advertising; the badge is now discoverable.
+- `adapter.SetConnectHandler` — the correct way to track connection state; `txChar.Write()` always returns `nil` on nRF52840 regardless of whether a central is connected.
-- The `WriteEvent` callback runs when the central writes to a characteristic. It runs in a BLE interrupt context — keep it short.
+- Keep BLE callbacks short and flag-only — calling SoftDevice functions (like `adv.Start()`) or SPI ops from within a SoftDevice event handler causes a deadlock.
 
 ---
 
@@ -594,6 +616,8 @@ A custom service exposes a single writable characteristic. The central writes 3
 |---|---|---|---|
 | LED Color | `BADA5502-…` | Write, WriteWithoutResponse | Central → Badge |
 
+The `WriteEvent` callback handles the color update directly (SPI and GPIO — no SoftDevice re-entry). Connection tracking uses the same flag pattern as step1.
+
 ```go
 WriteEvent: func(client bluetooth.Connection, offset int, value []byte) {
     if len(value) < 3 {
@@ -605,7 +629,25 @@ WriteEvent: func(client bluetooth.Connection, offset int, value []byte) {
 },
 ```
 
-After all services are registered the main goroutine simply blocks with `select {}` — all activity is driven by the BLE callback.
+```go
+adapter.SetConnectHandler(func(device bluetooth.Device, c bool) {
+    connected = c
+    connChanged = true
+})
+// ...
+for {
+    if connChanged {
+        connChanged = false
+        if connected {
+            drawStatus("Connected   ")
+        } else {
+            drawStatus("Advertising...")
+            adv.Start()
+        }
+    }
+    time.Sleep(100 * time.Millisecond)
+}
+```
 
 ```sh
 tinygo flash -target nicenano ./ble/step2
@@ -619,7 +661,7 @@ tinygo flash -target nicenano ./ble/step2
 
 **Key concepts**
 - Custom 128-bit UUIDs let you define entirely private services not shared with any standard profile.
-- `select {}` is idiomatic Go for blocking forever; it is more explicit than `for {}` with a sleep.
+- `WriteEvent` can call SPI and GPIO safely — it only avoids re-entering the SoftDevice (e.g. `adv.Start()`).
 - Always validate `len(value)` in `WriteEvent` — a malformed write should not panic.
 
 ---
@@ -628,20 +670,28 @@ tinygo flash -target nicenano ./ble/step2
 
 **Goal:** put the radio in observer mode and display nearby BLE devices.
 
-In scanner mode the badge does not advertise — it only listens. `adapter.Scan` is a blocking call, so it runs in a goroutine while the main loop updates the display every 500 ms.
+`adapter.Scan` is a blocking call that drives its own internal event loop via `sd_app_evt_wait` — the nRF52840 SoftDevice primitive for waiting on BLE events. While inside this loop, **TinyGo's cooperative scheduler never gets CPU time**, so goroutines spawned to call `adapter.StopScan()` after a timeout never run.
+
+Running `adapter.Scan` and SPI display operations concurrently causes a second problem: the SoftDevice can hold interrupts during event processing, and TinyGo's SPI driver waits for a DMA-completion interrupt using `wfe` (Wait For Event). If the SoftDevice consumes that wake-up event, the SPI transfer hangs forever.
+
+The solution for both problems is to call `adapter.StopScan()` **from inside the scan callback** using `time.Since`:
 
 ```go
-go func() {
+scanStart := time.Now()
 adapter.Scan(func(a *bluetooth.Adapter, result bluetooth.ScanResult) {
-        name := result.LocalName()
+    if time.Since(scanStart) >= scanWindow {
-        if name == "" {
+        adapter.StopScan() // causes adapter.Scan to return
-            name = result.Address.String()
+        return
     }
-        // deduplicate by address, update RSSI
+    // deduplicate by address, update RSSI, copy name bytes
 })
-}()
+
+// adapter.Scan has returned — SPI is safe to use now
+drawDevices()
 ```
 
+Device names and addresses are stored as fixed-size byte arrays, not `string` fields. Strings returned by `result.LocalName()` and `result.Address.String()` may point into SoftDevice-managed buffers that are recycled after the callback returns; accessing them later from the main loop causes memory corruption.
+
 RSSI (Received Signal Strength Indicator) is expressed in dBm — closer to 0 is stronger. The display colors devices by signal quality:
 
 | RSSI | Color | Meaning |
@@ -657,8 +707,10 @@ tinygo flash -target nicenano ./ble/step3
 Up to 5 nearby devices are listed by name and signal strength. Press **button A** to clear the list and start fresh.
 
 **Key concepts**
-- `result.LocalName()` returns the advertised name, if any. Devices that don't advertise a name are identified by their MAC address.
+- `adapter.Scan` runs its own internal `sd_app_evt_wait` loop — it never yields to TinyGo's cooperative scheduler. A goroutine that calls `StopScan()` after a `time.Sleep` will never execute while `Scan` is running.
-- TinyGo uses a cooperative scheduler — goroutines yield at blocking calls (`Scan`, `Sleep`, channel ops). Shared variables accessed from both the goroutine and the main loop are safe here because the scheduler is cooperative, but in general you should use channels or atomics.
+- On nRF52840, **never run SPI and `adapter.Scan` at the same time**. The SoftDevice can consume the WFE wake-up that TinyGo's SPI driver needs to detect DMA completion, causing the SPI bus to hang indefinitely. Always stop the scan before doing any display update.
+- **BLE callbacks must not store strings** that point into SoftDevice buffers. Use fixed-size `[N]byte` arrays and `copy()` in callbacks; convert to `string` only in the main loop.
+- `result.LocalName()` returns the advertised name, if any. Devices that don't advertise a name are shown by their MAC address (`result.Address.String()`).
 
 ---
 

tutorial/ble/step1/main.go

@@ -11,7 +11,7 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/tinygo-org/bluetooth"
+	"tinygo.org/x/bluetooth"
 	"tinygo.org/x/drivers/st7789"
 	"tinygo.org/x/tinyfont"
 	"tinygo.org/x/tinyfont/freesans"
@@ -38,6 +38,7 @@ var (
 var (
 	display      st7789.Device
 	connected    bool
+	connChanged  bool
 	counter      int
 )
 
@@ -49,12 +50,21 @@ var (
 )
 
 func main() {
+	// sometimes, a little wait is needed to initialize it at hardware level
+	time.Sleep(2 * time.Second)
 	initDisplay()
 	drawStatus("Advertising...")
 	drawCounter(0)
 
 	must("enable BLE", adapter.Enable())
 
+	adv := adapter.DefaultAdvertisement()
+
+	must("configure adv", adv.Configure(bluetooth.AdvertisementOptions{
+		LocalName: "NiceBadge",
+	}))
+
+	// AddService must be called before adv.Start() on nRF52840 SoftDevice.
 	var txChar bluetooth.Characteristic
 
 	must("add service", adapter.AddService(&bluetooth.Service{
@@ -78,32 +88,31 @@ func main() {
 		},
 	}))
 
-	adv := adapter.DefaultAdvertisement()
+	// Only set flags here — calling adv.Start() or display ops from within
-	must("configure adv", adv.Configure(bluetooth.AdvertisementOptions{
+	// the SoftDevice event callback causes a deadlock on nRF52840.
-		LocalName:    "NiceBadge",
+	adapter.SetConnectHandler(func(device bluetooth.Device, c bool) {
-		ServiceUUIDs: []bluetooth.UUID{serviceUUID},
+		connected = c
-	}))
+		connChanged = true
+	})
+
 	must("start adv", adv.Start())
 
 	for {
-		counter++
+		if connChanged {
-		drawCounter(counter)
+			connChanged = false
-
-		// Write sends a BLE notification to subscribed centrals.
-		// If no device is subscribed, Write returns an error.
-		_, err := txChar.Write([]byte(strconv.Itoa(counter) + "\n"))
-
-		wasConnected := connected
-		connected = err == nil
-		if wasConnected != connected {
 			if connected {
 				drawStatus("Connected   ")
 			} else {
 				drawStatus("Advertising...")
-				must("restart adv", adv.Start())
+				adv.Start()
 			}
 		}
 
+		counter++
+		drawCounter(counter)
+		if connected {
+			txChar.Write([]byte(strconv.Itoa(counter) + "\n"))
+		}
 		time.Sleep(time.Second)
 	}
 }

tutorial/ble/step2/main.go

@@ -14,8 +14,9 @@ import (
 	"image/color"
 	"machine"
 	"strconv"
+	"time"
 
-	"github.com/tinygo-org/bluetooth"
+	"tinygo.org/x/bluetooth"
 	"tinygo.org/x/drivers/st7789"
 	"tinygo.org/x/drivers/ws2812"
 	"tinygo.org/x/tinyfont"
@@ -39,24 +40,27 @@ var (
 	display      st7789.Device
 	leds         ws2812.Device
 	connected    bool
+	connChanged  bool
 	ledColor     color.RGBA
+	colorChanged bool
 )
 
 var (
 	black = color.RGBA{0, 0, 0, 255}
 	cyan  = color.RGBA{0, 200, 255, 255}
 	white = color.RGBA{255, 255, 255, 255}
-	gray  = color.RGBA{150, 150, 150, 255}
 )
 
 func main() {
+	time.Sleep(2 * time.Second)
 	initDisplay()
 	initLEDs()
 	drawStatus("Advertising...")
-	drawColor(color.RGBA{0, 0, 0, 255})
+	drawColor(color.RGBA{})
 
 	must("enable BLE", adapter.Enable())
 
+	// AddService must be called before adv.Start() on nRF52840 SoftDevice.
 	must("add service", adapter.AddService(&bluetooth.Service{
 		UUID: ledServiceUUID,
 		Characteristics: []bluetooth.CharacteristicConfig{
@@ -67,29 +71,45 @@ func main() {
 					if len(value) < 3 {
 						return
 					}
-					// value[0]=R, value[1]=G, value[2]=B
+					// Only assign values — no heap allocs (strconv, string concat)
+					// allowed in interrupt context on nRF52840.
 					ledColor = color.RGBA{value[0], value[1], value[2], 255}
-					setLEDs(ledColor)
+					colorChanged = true
-					drawColor(ledColor)
-
-					if !connected {
-						connected = true
-						drawStatus("Connected   ")
-					}
 				},
 			},
 		},
 	}))
 
+	// Only set flags here — calling adv.Start() or display ops from within
+	// the SoftDevice event callback causes a deadlock on nRF52840.
+	adapter.SetConnectHandler(func(device bluetooth.Device, c bool) {
+		connected = c
+		connChanged = true
+	})
+
 	adv := adapter.DefaultAdvertisement()
 	must("configure adv", adv.Configure(bluetooth.AdvertisementOptions{
 		LocalName: "NiceBadge",
-		ServiceUUIDs: []bluetooth.UUID{ledServiceUUID},
 	}))
 	must("start adv", adv.Start())
 
-	// wait forever; all logic is driven by the BLE WriteEvent callback
+	for {
-	select {}
+		if connChanged {
+			connChanged = false
+			if connected {
+				drawStatus("Connected   ")
+			} else {
+				drawStatus("Advertising...")
+				adv.Start()
+			}
+		}
+		if colorChanged {
+			colorChanged = false
+			setLEDs(ledColor)
+			drawColor(ledColor)
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
 }
 
 func initDisplay() {
@@ -127,7 +147,6 @@ func drawStatus(status string) {
 }
 
 func drawColor(c color.RGBA) {
-	// show a filled rectangle with the current color and its RGB values below
 	display.FillRectangle(0, 38, 240, 60, color.RGBA{c.R, c.G, c.B, 255})
 	display.FillRectangle(0, 100, 240, 35, black)
 	rgb := "R:" + strconv.Itoa(int(c.R)) +

tutorial/ble/step3/main.go

@@ -1,8 +1,8 @@
 package main
 
 // BLE scanner example.
-// Scans for nearby BLE devices and shows their names, addresses and signal
+// Scans for nearby BLE devices and shows their names and signal strength
-// strength (RSSI) on the display. Press button A to clear the list.
+// (RSSI) on the display. Press button A to clear the list.
 
 import (
 	"image/color"
@@ -10,17 +10,21 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/tinygo-org/bluetooth"
+	"tinygo.org/x/bluetooth"
 	"tinygo.org/x/drivers/st7789"
 	"tinygo.org/x/tinyfont"
 	"tinygo.org/x/tinyfont/freesans"
 )
 
 const maxDevices = 5
+const maxNameLen = 16
+const scanWindow = 500 * time.Millisecond
 
+// Fixed-size byte arrays avoid dangling pointers into SoftDevice buffers.
 type bleDevice struct {
-	name string
+	name [maxNameLen]byte
-	addr string
+	nLen uint8
+	addr bluetooth.Address
 	rssi int16
 }
 
@@ -41,53 +45,56 @@ var (
 )
 
 func main() {
+	time.Sleep(2 * time.Second)
 	initDisplay()
 
 	btnA := machine.P1_06
 	btnA.Configure(machine.PinConfig{Mode: machine.PinInputPullup})
 
 	must("enable BLE", adapter.Enable())
-
 	drawHeader()
 
-	// scan runs in a goroutine; found devices are stored and displayed in the main loop
-	go func() {
-		adapter.Scan(func(a *bluetooth.Adapter, result bluetooth.ScanResult) {
-			name := result.LocalName()
-			if name == "" {
-				name = result.Address.String()
-			}
-
-			// update existing entry if already seen, otherwise add new
-			found := false
-			for i := 0; i < count; i++ {
-				if devices[i].addr == result.Address.String() {
-					devices[i].rssi = result.RSSI
-					found = true
-					break
-				}
-			}
-			if !found && count < maxDevices {
-				devices[count] = bleDevice{
-					name: name,
-					addr: result.Address.String(),
-					rssi: result.RSSI,
-				}
-				count++
-			}
-		})
-	}()
-
 	for {
-		// button A clears the list
 		if !btnA.Get() {
 			count = 0
-			display.FillRectangle(0, 32, 240, 103, black)
 			time.Sleep(200 * time.Millisecond)
 		}
 
+		// adapter.Scan never yields to TinyGo's scheduler, so a goroutine
+		// calling StopScan() never gets CPU time.
+		// Fix: check elapsed time inside the callback and stop from there.
+		scanStart := time.Now()
+		adapter.Scan(func(a *bluetooth.Adapter, result bluetooth.ScanResult) {
+			if time.Since(scanStart) >= scanWindow {
+				adapter.StopScan()
+				return
+			}
+			for i := 0; i < count; i++ {
+				if devices[i].addr == result.Address {
+					devices[i].rssi = result.RSSI
+					return
+				}
+			}
+			if count >= maxDevices {
+				return
+			}
+			n := result.LocalName()
+			if n == "" {
+				n = result.Address.String()
+			}
+			nLen := len(n)
+			if nLen > maxNameLen {
+				nLen = maxNameLen
+			}
+			copy(devices[count].name[:], n)
+			devices[count].nLen = uint8(nLen)
+			devices[count].addr = result.Address
+			devices[count].rssi = result.RSSI
+			count++
+		})
+
+		// Scan has stopped — safe to use SPI now.
 		drawDevices()
-		time.Sleep(500 * time.Millisecond)
 	}
 }
 
@@ -111,11 +118,10 @@ func initDisplay() {
 }
 
 func drawHeader() {
-	tinyfont.WriteLine(&display, &freesans.Bold12pt7b, 10, 24, "BLE Scanner", cyan)
+	tinyfont.WriteLine(&display, &freesans.Regular9pt7b, 10, 24, "BLE Scanner", cyan)
 }
 
 func drawDevices() {
-	// clear device list area
 	display.FillRectangle(0, 32, 240, 103, black)
 
 	if count == 0 {
@@ -125,13 +131,9 @@ func drawDevices() {
 
 	for i := 0; i < count; i++ {
 		y := int16(52 + i*20)
-		name := devices[i].name
+		name := string(devices[i].name[:devices[i].nLen])
-		if len(name) > 16 {
-			name = name[:16]
-		}
 		rssi := " " + strconv.Itoa(int(devices[i].rssi)) + "dB"
 
-		// color by signal strength
 		c := white
 		if devices[i].rssi > -60 {
 			c = green