SAMx7x external clock

src/modm/board/samv71_xplained_ultra/board.hpp

@@ -25,7 +25,7 @@ using namespace modm::platform;
 
 struct SystemClock
 {
-	// 300MHz system clock generated by PLLA from internal Rc 12MHz clock
+	// 300 MHz system clock generated by PLLA from external 12 MHz crystal
 	static constexpr uint32_t PllAMult = 25;
 	static constexpr uint32_t Frequency = 300_MHz;
 	static constexpr uint32_t Mck = Frequency / 2;  // 150 MHz max.
@@ -35,10 +35,11 @@ struct SystemClock
 	static bool inline
 	enable()
 	{
-		ClockGen::setFlashLatency<Frequency / 2>();  // Flash runs off MCK
+		ClockGen::setFlashLatency<Mck>();
+
+		ClockGen::enableMainExternalCrystal<12_MHz>(std::chrono::microseconds{1000});
+		ClockGen::selectMainClockSource(MainClockSource::External);
 
-		ClockGen::enableMainInternal(MainInternalFreq::Rc12Mhz);
-		ClockGen::selectMainClockSource(MainClockSource::Internal);
 		ClockGen::enablePllA<PllAMult>();
 		ClockGen::selectMasterClk<MasterClkSource::PLLA_CLK, MasterClkPrescaler::CLK_1, MasterClkDivider::Div2>();
 		ClockGen::updateCoreFrequency<Frequency>();

src/modm/platform/clock/sam_pmc/clockgen.hpp.in

@@ -1,6 +1,7 @@
 /**
  * Copyright (c) 2021, Jeff McBride
  * Copyright (c) 2021, Tomasz Wasilczyk
+ * Copyright (c) 2023, Christopher Durand
  *
  * This file is part of the modm project.
  *
@@ -12,7 +13,8 @@
 
 #pragma once
 
-#include <stdint.h>
+#include <cstdint>
+#include <chrono>
 #include "../device.hpp"
 #include <modm/architecture/interface/delay.hpp>
 
@@ -267,8 +269,14 @@ public:
 	inline static void
 	enableMainInternal(MainInternalFreq freq);
 
+%% if target.family == "e7x/s7x/v7x"
+	template<uint32_t frequency>
+	static bool
+	enableMainExternalCrystal(std::chrono::microseconds startupTime);
+
 	inline static void
-	enableMainExternal(bool bypass);
+	enableMainExternalClock();
+%% endif
 
 	inline static void
 	selectMainClockSource(MainClockSource src);

src/modm/platform/clock/sam_pmc/clockgen_impl.hpp.in

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2021 Jeff McBride
  * Copyright (c) 2021, Tomasz Wasilczyk
+ * Copyright (c) 2023, Christopher Durand
  *
  * This file is part of the modm project.
  *
@@ -10,6 +11,8 @@
  */
 // ----------------------------------------------------------------------------
 
+#include <algorithm>
+
 namespace modm::platform
 {
 
@@ -28,6 +31,48 @@ ClockGen::enableMainInternal(MainInternalFreq freq)
 	while (!(PMC->PMC_SR & PMC_SR_MOSCRCS));
 }
 
+%% if target.family == "e7x/s7x/v7x"
+template<uint32_t frequency>
+bool
+ClockGen::enableMainExternalCrystal(std::chrono::microseconds startupTime)
+{
+	// disable external clock, clear startup time bits
+	PMC->CKGR_MOR = (PMC->CKGR_MOR | CKGR_MOR_KEY_PASSWD) &
+		~(CKGR_MOR_MOSCXTBY | CKGR_MOR_MOSCXTST_Msk);
+	// wait for external clock to shutdown
+	while (PMC->PMC_SR & PMC_SR_MOSCXTS);
+
+	// convert microseconds to startup time register value
+	// register unit is SCLK cycles (32768 Hz) multiplied by 8
+	const auto cycles = startupTime.count() * (32'768ll / 8) / 1'000'000;
+	const uint32_t timeSetting = std::clamp(cycles, 0ll, 255ll) << CKGR_MOR_MOSCXTST_Pos;
+
+	PMC->CKGR_MOR |= CKGR_MOR_KEY_PASSWD | CKGR_MOR_MOSCXTEN | timeSetting;
+	while (!(PMC->PMC_SR & PMC_SR_MOSCXTS));
+
+	// measure crystal frequency
+	PMC->CKGR_MCFR = CKGR_MCFR_CCSS | CKGR_MCFR_RCMEAS;
+	// two subsequent reads of MAINFRDY must be 1
+	while (!(PMC->CKGR_MCFR & CKGR_MCFR_MAINFRDY));
+	while (!(PMC->CKGR_MCFR & CKGR_MCFR_MAINFRDY));
+	const auto resultFrequency = ((PMC->CKGR_MCFR & CKGR_MCFR_MAINF_Msk) >> CKGR_MCFR_MAINF_Pos)
+		* (32768u / 16u);
+
+	// default slow clock has big tolerance (20 ... 57 kHz), only coarse check is safe
+	return (resultFrequency > (frequency / 2)) && (resultFrequency < (frequency * 2));
+}
+
+void
+ClockGen::enableMainExternalClock()
+{
+	// disable external crystal
+	PMC->CKGR_MOR = (PMC->CKGR_MOR | CKGR_MOR_KEY_PASSWD) & ~CKGR_MOR_MOSCXTEN;
+
+	// enable external clock input
+	PMC->CKGR_MOR |= CKGR_MOR_KEY_PASSWD | CKGR_MOR_MOSCXTBY;
+}
+%% endif
+
 void
 ClockGen::selectMainClockSource(MainClockSource src)
 {