From fbf7ac127fd7f28bebf853657e9cf8555dedca4d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vlastimil=20Slint=C3=A1k?= <slintak@uart.cz>
Date: Wed, 9 Jul 2025 11:52:51 +0200
Subject: [PATCH] Use TRNG for random numbers instead of analog input pin.

---
 NPR_14/source/config_flash.cpp | 40 +++++++++++++++++++++-------------
 NPR_14/source/config_flash.h   |  4 ++--
 NPR_14/source/main.cpp         |  6 +----
 3 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/NPR_14/source/config_flash.cpp b/NPR_14/source/config_flash.cpp
index 292b4b9..9db34a2 100644
--- a/NPR_14/source/config_flash.cpp
+++ b/NPR_14/source/config_flash.cpp
@@ -21,6 +21,7 @@
 #include "Eth_IPv4.h"
 #include "HMI_telnet.h"
 #include "TDMA.h"
+#include "trng_api.h"
 
 static unsigned char raw_config_data[260];
 static unsigned int config_index;
@@ -103,17 +104,21 @@ void virt_EEPROM_errase_all(void) {
 
 // higher level functions
 
-void NFPR_config_read(AnalogIn* analog_pin) {
+void NFPR_config_read(void) {
 	int i;
 	unsigned char default_config[260] = NFPR_default_config;
+	uint8_t random[2];
+
 	config_index = virt_EEPROM_read(raw_config_data);
 	if (config_index == 0) { //no previous config found
 		for (i=0; i<256; i++) {
 			raw_config_data[i] = default_config[i];
 		}
+
 		//MAC random 2 LSB values
-		raw_config_data[58] = NFPR_random_generator(analog_pin);
-		raw_config_data[59] = NFPR_random_generator(analog_pin);
+		NFPR_random_generator(random, sizeof(random));
+		raw_config_data[58] = random[0];
+		raw_config_data[59] = random[1];
 		raw_config_data[5] = raw_config_data[58];//callsign 1st char
 		raw_config_data[6] = raw_config_data[59];//callsign 2nd char
 		config_index = virt_EEPROM_write (raw_config_data, config_index);//save the MAC
@@ -127,19 +132,24 @@ void NFPR_config_read(AnalogIn* analog_pin) {
 	}
 }
 
-unsigned char NFPR_random_generator(AnalogIn* analog_pin) {
-	unsigned short interm_random;
-	unsigned char random_8;
-	int i;
-	random_8 = 0;
-	for (i=0; i<8; i++) {
-		interm_random = analog_pin->read_u16();
-		interm_random = (interm_random & 0x10)>>4;
-		interm_random = (interm_random << i);
-		random_8 = random_8 + interm_random;
-		wait_ms(4);
+/**
+ * Generate and save random `size` bytes into the `rnd` array.
+ * This code uses the STM32 TRNG HW.
+ * Returns `true` if the resulting data are random.
+ */
+bool NFPR_random_generator(uint8_t *rnd, size_t size) {
+	trng_t trng_obj;
+	size_t random_length = 0;
+
+	trng_init(&trng_obj);
+	trng_get_bytes(&trng_obj, rnd, size, &random_length);
+	trng_free(&trng_obj);
+
+	if(random_length == size) {
+		return true;
 	}
-	return random_8;
+
+	return false;
 }
 
 unsigned int NFPR_config_save(void) {
diff --git a/NPR_14/source/config_flash.h b/NPR_14/source/config_flash.h
index 3ad191c..0a94727 100644
--- a/NPR_14/source/config_flash.h
+++ b/NPR_14/source/config_flash.h
@@ -65,7 +65,7 @@
 
 unsigned int virt_EEPROM_read(unsigned char* data);
 
-unsigned char NFPR_random_generator(AnalogIn* analog_pin);
+bool NFPR_random_generator(uint8_t *rnd, size_t size);
 
 unsigned int virt_EEPROM_write(unsigned char* in_data, unsigned int previous_index);
 
@@ -77,7 +77,7 @@ void apply_config_from_raw_string(unsigned char* data_r);
 
 void write_config_to_raw_string (unsigned char* data_r);
 
-void NFPR_config_read(AnalogIn* analog_pin);
+void NFPR_config_read(void);
 
 unsigned int NFPR_config_save(void);
 
diff --git a/NPR_14/source/main.cpp b/NPR_14/source/main.cpp
index 4fa8744..f66611d 100644
--- a/NPR_14/source/main.cpp
+++ b/NPR_14/source/main.cpp
@@ -41,10 +41,6 @@ DigitalOut PTT_PA_pin(PA_0);//GPIO_10
 
 DigitalOut SI4463_SDN(PA_10);
 
-// TODO: Get random seed from somewhere else.
-// TODO: Random PIN is not present on the new PCB.
-AnalogIn Random_pin(PA_0);
-
 DigitalOut LED_RX_loc(PB_7);
 DigitalOut LED_connected(PA_4);
 
@@ -162,7 +158,7 @@ int main()
 	}
 	
 	wait_ms(100);
-	NFPR_config_read(&Random_pin);
+	NFPR_config_read();
 
 	//SI4463_print_version(G_SI4463);//!!!!
 	SI4463_get_state(G_SI4463);