Implement basic busy-wait waitReady method

Fixes #40

README.md

@@ -186,6 +186,8 @@ pi@raspberrypi:~/hx711 $ sudo bin/advancedhx711test 2 3 -377 -363712
 
 - `bool isReady( )`. Returns true if the HX711 chip has data ready to be retrieved.
 
+- `void waitReady( )`. When called, waits for the HX711 chip to have data ready, then returns.
+
 - `void setStrictTiming( bool strict )`. The HX711 chip has specific timing requirements which if not adhered to may lead to corrupt data. If strict timing is enabled, an `IntegrityException` will be thrown when data integrity cannot be guaranteed. However, given the unreliability of timing on a non-realtime OS (such as Raspbian on a Raspberry Pi), this in itself is unreliable and therefore disabled by default. Use at your own risk.
 
 - `bool isStrictTiming( )`. Returns true if strict timing is used.

include/HX711.h

@@ -127,6 +127,7 @@ class HX711 {
     void setConfig(const Channel c = Channel::A, const Gain g = Gain::GAIN_128);
 
     bool isReady() const;
+    virtual void waitReady();
     Value readValue();
 
     void powerDown();

include/SimpleHX711.h

@@ -42,6 +42,7 @@ class SimpleHX711 : public AbstractScale, public HX711 {
 
     virtual std::vector<Value> getValues(const std::chrono::nanoseconds timeout) override;
     virtual std::vector<Value> getValues(const std::size_t samples) override;
+    //no override for waitReady; SimpleHX711 is based on busy-waiting
 
 };
 };

src/HX711.cpp

@@ -258,10 +258,8 @@ void HX711::setConfig(const Channel c, const Gain g) {
          * A read must take place to set the gain at the
          * hardware level. See datasheet pg. 4 "Serial
          * Interface".
-         * 
-         * TODO: this is an inefficient busy-wait. Solutions?
          */
-        while(!this->isReady());
+        this->waitReady();
         this->readValue();
 
         /**
@@ -309,6 +307,12 @@ bool HX711::isReady() const {
 
 }
 
+void HX711::waitReady() const {
+    while(!this->isReady()) {
+        //nop; busy-wait
+    }
+}
+
 Value HX711::readValue() {
 
     std::int32_t v = 0;