From d841d250d8c0a3408904fd04ec5d5be115ded3ac Mon Sep 17 00:00:00 2001
From: Tom Pittenger <tom.pittenger@krausaerospace.com>
Date: Mon, 3 Jul 2023 18:18:21 -0700
Subject: [PATCH] AP_HAL_ChibiOS: allow HW without HW_RNG to SW-based create
 psuedo-random

---
 libraries/AP_HAL_ChibiOS/Util.cpp                | 16 +++++++++++-----
 .../AP_HAL_ChibiOS/hwdef/common/stm32_util.h     |  3 +++
 libraries/AP_HAL_ChibiOS/system.cpp              |  7 +++++++
 3 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/libraries/AP_HAL_ChibiOS/Util.cpp b/libraries/AP_HAL_ChibiOS/Util.cpp
index c49d882bfe..a27d4ad86a 100644
--- a/libraries/AP_HAL_ChibiOS/Util.cpp
+++ b/libraries/AP_HAL_ChibiOS/Util.cpp
@@ -705,9 +705,7 @@ bool Util::get_random_vals(uint8_t* data, size_t size)
 {
 #if HAL_USE_HW_RNG && defined(RNG)
     size_t true_random_vals = stm32_rand_generate_nonblocking(data, size);
-    if (true_random_vals == size) {
-        return true;
-    } else {
+    if (true_random_vals != size) {
         if (!(true_random_vals % 2)) {
             data[true_random_vals] = (uint8_t)(get_random16() & 0xFF);
             true_random_vals++;
@@ -718,10 +716,18 @@ bool Util::get_random_vals(uint8_t* data, size_t size)
             true_random_vals+=sizeof(uint16_t);
         }
     }
-    return true;
 #else
-    return false;
+    size_t true_random_vals = 0;
+    while(true_random_vals < size) {
+        uint16_t val = get_random16();
+        memcpy(&data[true_random_vals], &val, sizeof(uint16_t));
+        true_random_vals+=sizeof(uint16_t);
+    }
+    if (size % 2) {
+        data[size-1] = get_random16() & 0xFF;
+    }
 #endif
+    return true;
 }
 
 /**
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h b/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h
index a91c972596..73afbfa930 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.h
@@ -177,6 +177,9 @@ bool stm32_rand_generate_blocking(unsigned char* output, unsigned int sz, uint32
 unsigned int stm32_rand_generate_nonblocking(unsigned char* output, unsigned int sz);
 #endif
 
+// To be defined in HAL code
+extern uint32_t chibios_rand_generate(void);
+
 void stm32_flash_protect_flash(bool bootloader, bool protect);
 void stm32_flash_unprotect_flash(void);
 
diff --git a/libraries/AP_HAL_ChibiOS/system.cpp b/libraries/AP_HAL_ChibiOS/system.cpp
index 82b948fce3..9a827d518d 100644
--- a/libraries/AP_HAL_ChibiOS/system.cpp
+++ b/libraries/AP_HAL_ChibiOS/system.cpp
@@ -304,6 +304,13 @@ void __entry_hook()
 }
 #endif
 
+uint32_t chibios_rand_generate()
+{
+    uint32_t val;
+    hal.util->get_random_vals((uint8_t*)&val, sizeof(val));
+    return val;
+}
+
 }
 namespace AP_HAL {