AP_HAL: proper RCInput interface specification

libraries/AP_HAL/RCInput.h

@@ -4,10 +4,32 @@
 
 #include "AP_HAL_Namespace.h"
 
+#define RC_INPUT_MIN_PULSEWIDTH 900
+#define RC_INPUT_MAX_PULSEWIDTH 2100
+
 class AP_HAL::RCInput {
 public:
-    RCInput() {}
-    virtual void init(int machtnicht) = 0;
+    /**
+     * Call init from the platform hal instance init, so that both the type of
+     * the RCInput implementation and init argument (e.g. ISRRegistry) are
+     * known to the programmer. (Its too difficult to describe this dependency
+     * in the C++ type system.)
+     */
+    virtual void init(void* implspecific) = 0;
+
+    /**
+     * Return the number of currently valid channels.
+     * Typically 0 (no valid radio channels) or 8 (implementation-defined)
+     * Could be less than or greater than 8 depending on your incoming radio
+     * or PPM stream
+     */
+    virtual uint8_t  valid() = 0;
+
+    /* Read a single channel at a time */
+    virtual uint16_t read(uint8_t ch) = 0;
+
+    /* Read an array of channels, return the valid count */
+    virtual uint8_t read(uint16_t* periods, uint8_t len) = 0;
 };
 
 #endif // __AP_HAL_RC_INPUT_H__