[Si443x] Fixed known binary receive length

src/modules/Si443x/Si443x.cpp

@@ -285,14 +285,22 @@ int16_t Si443x::readData(uint8_t* data, size_t len) {
   clearIRQFlags();
 
   // get packet length
-  size_t length = len;
-  if(len == RADIOLIB_SI443X_MAX_PACKET_LENGTH) {
-    length = getPacketLength();
+  size_t length = getPacketLength();
+  size_t dumpLen = 0;
+  if((len != 0) && (len < length)) {
+    // user requested less data than we got, only return what was requested
+    dumpLen = length - len;
+    length = len;
   }
 
   // read packet data
   _mod->SPIreadRegisterBurst(RADIOLIB_SI443X_REG_FIFO_ACCESS, length, data);
 
+  // dump the bytes that weren't requested
+  if(dumpLen != 0) {
+    clearFIFO(dumpLen);
+  }
+
   // clear internal flag so getPacketLength can return the new packet length
   _packetLengthQueried = false;
 
@@ -647,6 +655,13 @@ void Si443x::clearIRQFlags() {
   _mod->SPIreadRegisterBurst(RADIOLIB_SI443X_REG_INTERRUPT_STATUS_1, 2, buff);
 }
 
+void Si443x::clearFIFO(size_t count) {
+  while(count) {
+    _mod->SPIreadRegister(RADIOLIB_SI443X_REG_FIFO_ACCESS);
+    count--;
+  }
+}
+
 int16_t Si443x::config() {
   // set mode to standby
   int16_t state = standby();

src/modules/Si443x/Si443x.h

@@ -695,7 +695,8 @@ class Si443x: public PhysicalLayer {
 
       \param data Pointer to array to save the received binary data.
 
-      \param len Number of bytes that will be received. Must be known in advance for binary transmissions.
+      \param len Number of bytes that will be read. When set to 0, the packet length will be retreived automatically.
+      When more bytes than received are requested, only the number of bytes requested will be returned.
 
       \returns \ref status_codes
     */
@@ -838,6 +839,7 @@ class Si443x: public PhysicalLayer {
 #endif
     bool findChip();
     void clearIRQFlags();
+    void clearFIFO(size_t count);
     int16_t config();
     int16_t updateClockRecovery();
     int16_t directMode();