dev: Add a dummy serial device

Add a dummy serial device that discards any output and doesn't provide
any input. This device can be used to terminate UARTs that don't have
a default device (e.g., a terminal) attached.

Change-Id: I4a6b0b5037ce360f59bfb5c566e1698d113a1d26
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/4290
Reviewed-by: Gabe Black <gabeblack@google.com>

src/dev/Serial.py

@@ -42,3 +42,7 @@ class SerialDevice(SimObject):
     type = 'SerialDevice'
     abstract = True
     cxx_header = "dev/serial.hh"
+
+class SerialNullDevice(SerialDevice):
+    type = 'SerialNullDevice'
+    cxx_header = "dev/serial.hh"

src/dev/serial.cc

@@ -41,6 +41,7 @@
 
 #include "base/misc.hh"
 #include "params/SerialDevice.hh"
+#include "params/SerialNullDevice.hh"
 
 SerialDevice::SerialDevice(const SerialDeviceParams *p)
     : SimObject(p), interfaceCallback(nullptr)
@@ -71,3 +72,24 @@ SerialDevice::notifyInterface()
         interfaceCallback->process();
 }
 
+
+
+
+SerialNullDevice::SerialNullDevice(const SerialNullDeviceParams *p)
+    : SerialDevice(p)
+{
+}
+
+uint8_t
+SerialNullDevice::readData()
+{
+    panic("SerialNullDevice does not have pending data.\n");
+}
+
+
+
+SerialNullDevice *
+SerialNullDeviceParams::create()
+{
+    return new SerialNullDevice(this);
+}

src/dev/serial.hh

@@ -44,6 +44,7 @@
 #include "sim/sim_object.hh"
 
 struct SerialDeviceParams;
+struct SerialNullDeviceParams;
 
 /**
  * Base class for serial devices such as terminals.
@@ -140,4 +141,18 @@ class SerialDevice : public SimObject
     Callback *interfaceCallback;
 };
 
+/**
+ * Dummy serial device that discards all data sent to it.
+ */
+class SerialNullDevice : public SerialDevice
+{
+  public:
+    SerialNullDevice(const SerialNullDeviceParams *p);
+
+  public:
+    bool dataAvailable() const override { return false; }
+    void writeData(uint8_t c) override {};
+    uint8_t readData() override;
+};
+
 #endif // __DEV_SERIAL_HH__