From 84bbee784deaaf8fbb300f2d3d5e5e601e99572d Mon Sep 17 00:00:00 2001
From: Alexandre Abadie <alexandre.abadie@inria.fr>
Date: Mon, 24 Aug 2020 14:06:15 +0200
Subject: [PATCH 1/2] cpu/stm32: add transition phase when raising +80MHz clock

---
 cpu/stm32/stmclk/stmclk_gx.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/cpu/stm32/stmclk/stmclk_gx.c b/cpu/stm32/stmclk/stmclk_gx.c
index 30e6e257da..396e53615f 100644
--- a/cpu/stm32/stmclk/stmclk_gx.c
+++ b/cpu/stm32/stmclk/stmclk_gx.c
@@ -155,9 +155,23 @@ void stmclk_init_sysclk(void)
     RCC->CR |= RCC_CR_PLLON;
     while (!(RCC->CR & RCC_CR_PLLRDY)) {}
 
+#if CLOCK_AHB > MHZ(80)
+    /* Divide HCLK by before enabling the PLL */
+    RCC->CFGR |= RCC_CFGR_HPRE_DIV2;
+#endif
+
     /* now that the PLL is running, we use it as system clock */
     RCC->CFGR |= RCC_CFGR_SW_PLL;
     while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_PLL) {}
+
+#if CLOCK_AHB > MHZ(80)
+    /* Wait 1us before switching back to full speed */
+    /* Use volatile to prevent the compiler from optimizing the loop */
+    volatile uint8_t count = CLOCK_CORECLOCK / MHZ(1);
+    while (count--) {}
+    RCC->CFGR &= ~RCC_CFGR_HPRE_DIV2;
+#endif
+
 #endif
 
     stmclk_disable_hsi();

From d15d123eef2d43ce4ce55f9c3d1ac12e0c3f679a Mon Sep 17 00:00:00 2001
From: Alexandre Abadie <alexandre.abadie@inria.fr>
Date: Mon, 24 Aug 2020 15:28:13 +0200
Subject: [PATCH 2/2] boards/stm32g4: enable max 170MHz clock by default

---
 boards/common/stm32/include/g4/cfg_clock_default.h | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/boards/common/stm32/include/g4/cfg_clock_default.h b/boards/common/stm32/include/g4/cfg_clock_default.h
index 19615da177..af258a87be 100644
--- a/boards/common/stm32/include/g4/cfg_clock_default.h
+++ b/boards/common/stm32/include/g4/cfg_clock_default.h
@@ -48,15 +48,10 @@ extern "C" {
 #define CLOCK_CORECLOCK     (CLOCK_HSE)
 
 #elif CLOCK_USE_PLL
-/* The following parameters configure a 80MHz system clock with HSE as input clock */
-#define CLOCK_PLL_M         (6)
-#define CLOCK_PLL_N         (40)
-#define CLOCK_PLL_R         (2)
-/* Use the following to reach 170MHz
+/* The following parameters configure a 170MHz system clock with HSE as input clock */
 #define CLOCK_PLL_M          (6)
 #define CLOCK_PLL_N          (85)
 #define CLOCK_PLL_R          (2)
-*/
 #if CLOCK_HSE
 #define CLOCK_PLL_SRC       (CLOCK_HSE)
 #else /* CLOCK_HSI */