[docs] update Doxygen groupings for new APIs (#4166)
diff --git a/include/openthread/error.h b/include/openthread/error.h
index 3c4c2d5..3d7b749 100644
--- a/include/openthread/error.h
+++ b/include/openthread/error.h
@@ -123,11 +123,20 @@
* @defgroup api-crypto Crypto
* @defgroup api-entropy Entropy Source
* @defgroup api-factory-diagnostics Factory Diagnostics
+ * @defgroup api-heap Heap
* @defgroup api-jam-detection Jam Detection
* @defgroup api-logging Logging
* @defgroup api-ncp Network Co-Processor
* @defgroup api-network-time Network Time Synchronization
- * @defgroup api-random Random Number Generator
+ * @defgroup api-random-group Random Number Generator
+ *
+ * @{
+ *
+ * @defgroup api-random-crypto RNG Cryptographic
+ * @defgroup api-random-non-crypto RNG Non-cryptographic
+ *
+ * @}
+ *
* @defgroup api-sntp SNTP
*
* @}
diff --git a/include/openthread/random_crypto.h b/include/openthread/random_crypto.h
index 42900ae..da4ba7b 100644
--- a/include/openthread/random_crypto.h
+++ b/include/openthread/random_crypto.h
@@ -45,7 +45,7 @@
#endif
/**
- * @addtogroup api-random
+ * @addtogroup api-random-crypto
*
* @brief
* This module includes functions that generates cryptographic random numbers.
diff --git a/include/openthread/random_noncrypto.h b/include/openthread/random_noncrypto.h
index 6b07cbc..40bb260 100644
--- a/include/openthread/random_noncrypto.h
+++ b/include/openthread/random_noncrypto.h
@@ -42,7 +42,7 @@
#endif
/**
- * @addtogroup api-random
+ * @addtogroup api-random-non-crypto
*
* @brief
* This module includes functions that generates non cryptographic random numbers.
