AP_HAL_SITL: sim: namespace for specifying SITL devices from cmdline

libraries/AP_HAL_SITL/SITL_State.cpp

@@ -191,6 +191,12 @@ void SITL_State::wait_clock(uint64_t wait_time_usec)
     }
 }
 
+#define streq(a, b) (!strcmp(a, b))
+int SITL_State::sim_fd(const char *name, const char *arg)
+{
+    AP_HAL::panic("unknown simulated device: %s", name);
+}
+
 #ifndef HIL_MODE
 /*
   check for a SITL RC input packet

libraries/AP_HAL_SITL/SITL_State.h

@@ -52,6 +52,10 @@ public:
         return _base_port;
     }
 
+    // create a file desciptor attached to a virtual device; type of
+    // device is given by name parameter
+    int sim_fd(const char *name, const char *arg);
+
     bool use_rtscts(void) const {
         return _use_rtscts;
     }

libraries/AP_HAL_SITL/UARTDriver.cpp

@@ -67,6 +67,7 @@ void UARTDriver::begin(uint32_t baud, uint16_t rxSpace, uint16_t txSpace)
              tcp:0:wait       // tcp listen on use base_port + 0
              tcpclient:192.168.2.15:5762
              uart:/dev/ttyUSB0:57600
+             sim:ParticleSensor_SDS021:
          */
         char *saveptr = nullptr;
         char *s = strdup(path);
@@ -89,6 +90,12 @@ void UARTDriver::begin(uint32_t baud, uint16_t rxSpace, uint16_t txSpace)
             _uart_path = strdup(args1);
             _uart_baudrate = baudrate;
             _uart_start_connection();
+        } else if (strcmp(devtype, "sim") == 0) {
+            ::printf("SIM connection %s:%s\n", args1, args2);
+            if (!_connected) {
+                _connected = true;
+                _fd = _sitlState->sim_fd(args1, args2);
+            }
         } else {
             AP_HAL::panic("Invalid device path: %s", path);
         }