Ability to disable RSSI-based random number generator in radio.c

src/lmic/config.h

@@ -151,6 +151,14 @@
 # error "You may define at most one of USE_ORIGINAL_AES and USE_IDEETRON_AES"
 #endif
 
+
+// By default LMIC use the radio to gather random seed from wideband RSSI
+// measurements. Extracting good quality random seed takes 480 SPI transactions
+// on average. This flag allows alternative random implementations, like
+// true-RNGs built-in to many MCUs. Use in conjuction with os_getRndU1.
+// define this in lmic_project_config.h to disable radio.c random number generator
+//#define LMIC_DISABLE_RADIO_RAND
+
 // LMIC_DISABLE_DR_LEGACY
 // turn off legacy DR_* symbols that vary by bandplan.
 // Older code uses these for configuration. EU868_DR_*, US915_DR_*

src/lmic/oslmic.h

@@ -92,9 +92,6 @@ extern u4_t AESKEY[];
 #define AESaux ((u1_t*)AESAUX)
 #define FUNC_ADDR(func) (&(func))
 
-u1_t radio_rand1 (void);
-#define os_getRndU1() radio_rand1()
-
 #define DEFINE_LMIC  struct lmic_t LMIC
 #define DECLARE_LMIC extern struct lmic_t LMIC
 
@@ -114,6 +111,7 @@ void os_init (void);
 int os_init_ex (const void *pPinMap);
 void os_runloop (void);
 void os_runloop_once (void);
+u1_t radio_rand1 (void);
 u1_t radio_rssi (void);
 void radio_monitor_rssi(ostime_t n, oslmic_radio_rssi_t *pRssi);
 
@@ -222,26 +220,30 @@ bit_t os_queryTimeCriticalJobs(ostime_t time);
 u4_t os_rlsbf4 (xref2cu1_t buf);
 #endif
 #ifndef os_wlsbf4
-//! Write 32-bit quntity into buffer in little endian byte order.
+//! Write 32-bit quantity into buffer in little endian byte order.
 void os_wlsbf4 (xref2u1_t buf, u4_t value);
 #endif
 #ifndef os_rmsbf4
 //! Read 32-bit quantity from given pointer in big endian byte order.
 u4_t os_rmsbf4 (xref2cu1_t buf);
 #endif
 #ifndef os_wmsbf4
-//! Write 32-bit quntity into buffer in big endian byte order.
+//! Write 32-bit quantity into buffer in big endian byte order.
 void os_wmsbf4 (xref2u1_t buf, u4_t value);
 #endif
 #ifndef os_rlsbf2
 //! Read 16-bit quantity from given pointer in little endian byte order.
 u2_t os_rlsbf2 (xref2cu1_t buf);
 #endif
 #ifndef os_wlsbf2
-//! Write 16-bit quntity into buffer in little endian byte order.
+//! Write 16-bit quantity into buffer in little endian byte order.
 void os_wlsbf2 (xref2u1_t buf, u2_t value);
 #endif
 
+//! Get random number (default impl for u1_t).
+#ifndef os_getRndU1
+#define os_getRndU1() radio_rand1()
+#endif
 //! Get random number (default impl for u2_t).
 #ifndef os_getRndU2
 #define os_getRndU2() ((u2_t)((os_getRndU1()<<8)|os_getRndU1()))

src/lmic/radio.c

@@ -373,9 +373,12 @@
 #error Missing CFG_sx1272_radio/CFG_sx1276_radio
 #endif
 
+
+#if !defined(LMIC_DISABLE_RADIO_RAND)
 // RADIO STATE
 // (initialized by radio_init(), used by radio_rand1())
 static u1_t randbuf[16];
+#endif
 
 
 static void writeReg (u1_t addr, u1_t data ) {
@@ -1117,21 +1120,26 @@ int radio_init () {
 #else
 #error Missing CFG_sx1272_radio/CFG_sx1276_radio
 #endif
+
     // set the tcxo input, if needed
     if (hal_queryUsingTcxo())
         writeReg(RegTcxo, readReg(RegTcxo) | RegTcxo_TcxoInputOn);
 
+#if !defined(LMIC_DISABLE_RADIO_RAND)
     // seed 15-byte randomness via noise rssi
     rxlora(RXMODE_RSSI);
     while( (readReg(RegOpMode) & OPMODE_MASK) != OPMODE_RX ); // continuous rx
     for(int i=1; i<16; i++) {
         for(int j=0; j<8; j++) {
+            // von Neumann extractor:
+            // creates uniform distribution random from a non-uniformly distributed random source.
             u1_t b; // wait for two non-identical subsequent least-significant bits
             while( (b = readReg(LORARegRssiWideband) & 0x01) == (readReg(LORARegRssiWideband) & 0x01) );
             randbuf[i] = (randbuf[i] << 1) | b;
         }
     }
     randbuf[0] = 16; // set initial index
+#endif
 
 #ifdef CFG_sx1276mb1_board
     // chain calibration
@@ -1157,6 +1165,7 @@ int radio_init () {
     return 1;
 }
 
+#if !defined(LMIC_DISABLE_RADIO_RAND)
 // return next random byte derived from seed buffer
 // (buf[0] holds index of next byte to be returned)
 u1_t radio_rand1 () {
@@ -1170,6 +1179,7 @@ u1_t radio_rand1 () {
     randbuf[0] = i;
     return v;
 }
+#endif
 
 u1_t radio_rssi () {
     u1_t r = readReg(LORARegRssiValue);