gateware.usb2: add disconnect signal to USBResetSequencer

luna/gateware/usb/usb2/device.py

@@ -243,6 +243,8 @@ def elaborate(self, platform):
 
             reset_sequencer.vbus_connected  .eq(~self.utmi.session_end),
             reset_sequencer.line_state      .eq(self.utmi.line_state),
+
+            reset_sequencer.disconnect      .eq(~self.connect),
         ]
 
 

luna/gateware/usb/usb2/reset.py

@@ -65,6 +65,8 @@ class USBResetSequencer(Elaboratable):
         be held in perpetual bus reset, and reset handshaking will be disabled.
     line_state: Signal(2), input
         The UTMI linestate signals; used to read the current state of the USB D+ and D- lines.
+    disconnect: Signal(), input
+        If set, the device will be switched into non-driving operating mode to force a host disconnect.
 
     bus_reset: Signal(), output
         Strobe; pulses high for one cycle when a bus reset is detected. This signal indicates that the
@@ -123,6 +125,8 @@ def __init__(self):
         self.vbus_connected     = Signal()
         self.line_state         = Signal(2)
 
+        self.disconnect         = Signal()
+
         self.bus_reset          = Signal()
         self.suspended          = Signal()
 
@@ -166,7 +170,7 @@ def elaborate(self, platform):
         with m.If(self.current_speed == USBSpeed.HIGH):
             m.d.comb += bus_idle.eq(self.line_state == self._LINE_STATE_SQUELCH)
 
-        # Full and low-speed busses see a 'J' state when idle, due to the device pull-up restistors.
+        # Full and low-speed busses see a 'J' state when idle, due to the device pull-up resistors.
         # (The line_state values for these are flipped between speeds.) [USB2.0: 7.1.7.4.1; USB2.0: Table 7-2].
         with m.Elif(self.current_speed == USBSpeed.FULL):
             m.d.comb += bus_idle.eq(self.line_state == self._LINE_STATE_FS_HS_J)
@@ -200,7 +204,9 @@ def elaborate(self, platform):
                 # potential reset. Keep our timer at zero.
                 with m.If(self.line_state != self._LINE_STATE_SE0):
                     m.d.usb += timer.eq(0)
-
+                    # Enter forced disconnect when self.disconnect is high.
+                    with m.If(self.disconnect):
+                        m.next = "DISCONNECT"
 
                 # If VBUS isn't connected, don't go through the whole reset process;
                 # but also consider ourselves permanently in reset. This ensures we
@@ -242,6 +248,9 @@ def elaborate(self, platform):
                 # potential reset. Keep our timer at zero.
                 with m.If(self.line_state != self._LINE_STATE_SE0):
                     m.d.usb += timer.eq(0)
+                    # Enter forced disconnect when self.disconnect is high.
+                    with m.If(self.disconnect):
+                        m.next = "DISCONNECT"
 
                 # If VBUS isn't connected, our device/host relationship is effectively
                 # a blank state. We'll want to present our detection pull-up to the host,
@@ -508,4 +517,27 @@ def elaborate(self, platform):
                     with m.Else():
                         m.next = 'START_HS_DETECTION'
 
+
+            # DISCONNECT -- our device has entered a forced USB disconnect; hold the device in
+            # NON_DRIVING operating mode for Tddis=0.25us and wait for self.disconnect to go low.
+            with m.State('DISCONNECT'):
+                m.d.usb += self.operating_mode.eq(UTMIOperatingMode.NON_DRIVING)
+
+                # A disconnect condition is indicated if the host or hub is not driving the data lines and an
+                # SE0 persists on a downstream facing port for more than Tddis.
+                # [USB2.0: 7.1.7.3].
+                tddis = Signal()
+                with m.If(timer == self._CYCLES_2P5_MICROSECONDS):
+                    m.d.usb += tddis.eq(1)
+
+                # Exit DISCONNECT once the Tddis timer has expired and self.disconnect is low.
+                with m.If((~self.disconnect) & tddis):
+                    m.d.usb += [
+                        tddis.eq(0),
+                        self.current_speed.eq(USBSpeed.FULL),
+                        self.operating_mode.eq(UTMIOperatingMode.NORMAL),
+                        self.termination_select.eq(1),
+                    ]
+                    m.next = 'INITIALIZE'
+
         return m