AP_HAL: default to register checking every 10th call

this saves having this in nearly all callers

libraries/AP_HAL/Device.cpp

@@ -35,13 +35,15 @@
 /*
   setup nregs checked registers
  */
-bool AP_HAL::Device::setup_checked_registers(uint8_t nregs)
+bool AP_HAL::Device::setup_checked_registers(uint8_t nregs, uint8_t frequency)
 {
     if (_checked.regs != nullptr) {
         delete[] _checked.regs;
         _checked.n_allocated = 0;
         _checked.n_set = 0;
         _checked.next = 0;
+        _checked.frequency = frequency;
+        _checked.counter = 0;
     }
     _checked.regs = new struct checkreg[nregs];
     if (_checked.regs == nullptr) {
@@ -84,6 +86,11 @@ bool AP_HAL::Device::check_next_register(void)
     if (_checked.n_set == 0) {
         return true;
     }
+    if (++_checked.counter < _checked.frequency) {
+        return true;
+    }
+    _checked.counter = 0;
+    
     struct checkreg &reg = _checked.regs[_checked.next];
     uint8_t v;
     if (!read_registers(reg.regnum, &v, 1) || v != reg.value) {

libraries/AP_HAL/Device.h

@@ -121,9 +121,10 @@ public:
     void set_checked_register(uint8_t reg, uint8_t val);
 
     /**
-     * setup for register value checking
+     * setup for register value checking. Frequency is how often to check registers. If set to 10 then
+     * every 10th call to check_next_register will check a register
      */
-    bool setup_checked_registers(uint8_t num_regs);
+    bool setup_checked_registers(uint8_t num_regs, uint8_t frequency=10);
 
     /**
      * check next register value for correctness. Return false if value is incorrect
@@ -266,6 +267,8 @@ private:
         uint8_t n_allocated;
         uint8_t n_set;
         uint8_t next;
+        uint8_t frequency;
+        uint8_t counter;
         struct checkreg *regs;
     } _checked;
 };