fix: drain SPE status backlog so display is current (was ~15s stale); ON now pulses DTR (0x0B is level-only); power-level cycle waits for real status change

internal/spe/spe.go

@@ -146,30 +146,53 @@ func (c *Client) Operate(on bool) error {
 // ToggleOperate flips STANDBY/OPERATE unconditionally.
 func (c *Client) ToggleOperate() error { return c.sendCmd(cmdOperate) }
 
-// PowerOn presses the POWER key (turns the amp on when it's off).
-func (c *Client) PowerOn() error { return c.sendCmd(cmdPower) }
+// PowerOn turns the amplifier on. Per the SPE manual this is NOT a data command
+// but a hardware DTR pulse on the serial line (the "Remote_ON" pin), which needs
+// the special SPE cable — so it only applies to the serial transport. Over TCP
+// there is no DTR line and power-on isn't possible remotely.
+func (c *Client) PowerOn() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	sp, ok := c.conn.(serial.Port)
+	if !ok {
+		return fmt.Errorf("power-on needs the serial DTR line (special SPE cable); not available over network")
+	}
+	// A single positive pulse (~1.2s) on DTR, as the manual describes.
+	if err := sp.SetDTR(true); err != nil {
+		return err
+	}
+	time.Sleep(1200 * time.Millisecond)
+	return sp.SetDTR(false)
+}
 
 // PowerOff presses the OFF key (switches the amp off).
 func (c *Client) PowerOff() error { return c.sendCmd(cmdOff) }
 
 // SetPowerLevel cycles the output power level (L/M/H) to the requested one by
-// tapping the POWER key until the reported level matches, giving the amp time to
-// report each change. `level` is "L", "M" or "H" (case-insensitive).
+// tapping the POWER key (0x0B) and WAITING for the amp to actually report the new
+// level before the next tap — the status is streamed, so we poll GetStatus rather
+// than sleeping a fixed time. `level` is "L", "M" or "H" (case-insensitive).
 func (c *Client) SetPowerLevel(level string) error {
 	want := strings.ToUpper(strings.TrimSpace(level))
 	if want == "" {
 		return nil
 	}
-	// At most 3 taps to walk the 3-way cycle back around to the target.
+	// At most 3 taps to walk the 3-way L→M→H cycle around to the target.
 	for i := 0; i < 3; i++ {
-		cur := strings.ToUpper(strings.TrimSpace(c.GetStatus().PowerLevel))
-		if cur == want {
+		if strings.ToUpper(strings.TrimSpace(c.GetStatus().PowerLevel)) == want {
 			return nil
 		}
+		prev := strings.ToUpper(strings.TrimSpace(c.GetStatus().PowerLevel))
 		if err := c.sendCmd(cmdPower); err != nil {
 			return err
 		}
-		time.Sleep(1 * time.Second) // let the amp apply it and the poll refresh status
+		// Wait (up to ~2s) for the streamed status to reflect the change.
+		for w := 0; w < 20; w++ {
+			time.Sleep(100 * time.Millisecond)
+			if strings.ToUpper(strings.TrimSpace(c.GetStatus().PowerLevel)) != prev {
+				break
+			}
+		}
 	}
 	return nil
 }
@@ -186,6 +209,11 @@ func (c *Client) pollLoop() {
 				c.setErr(fmt.Errorf("connect: %w", err))
 				continue
 			}
+			// The amp streams status frames faster than one per poll, so a backlog
+			// builds up and we'd read stale frames (the display lagged ~15s behind
+			// the real amp). Flush anything pending, THEN request + read exactly one
+			// fresh frame — the status we show is always current.
+			c.drainInput()
 			if err := c.sendCmd(cmdStatus); err != nil {
 				c.mu.Lock()
 				c.dropLocked()
@@ -229,6 +257,32 @@ func (c *Client) dropLocked() {
 	}
 }
 
+// drainInput discards everything currently pending on the link (OS buffer + the
+// bufio reader) so the next read returns a fresh frame rather than a queued stale
+// one. Called before each status request.
+func (c *Client) drainInput() {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.conn == nil {
+		return
+	}
+	if sp, ok := c.conn.(serial.Port); ok {
+		_ = sp.ResetInputBuffer()
+	} else if nc, ok := c.conn.(net.Conn); ok {
+		_ = nc.SetReadDeadline(time.Now().Add(15 * time.Millisecond))
+		buf := make([]byte, 4096)
+		for {
+			n, err := nc.Read(buf)
+			if n == 0 || err != nil {
+				break
+			}
+		}
+	}
+	if c.r != nil {
+		c.r.Reset(c.conn)
+	}
+}
+
 // sendCmd frames one keystroke code and writes it. Single-byte payload → CHK is
 // the code itself.
 func (c *Client) sendCmd(code byte) error {