[example] Add delay measurement example

examples/nucleo_f303k8/blink/main.cpp

@@ -13,16 +13,104 @@
 
 using namespace Board;
 
+
+namespace modm
+{
+
+inline void
+delay_ns_inl(uint32_t ns)
+{
+	volatile uint32_t cycles;
+	// ns_per_loop = nanoseconds per cycle times cycles per loop ({{loop}} cycles)
+	asm volatile (
+		".syntax unified \n\t"
+		".align 4 \n\t"
+		"muls.n	%[ovhd], %[ovhd], %[dnpl] \n\t"	// multiply the overhead cycles with the ns per cycle:  1-2 cycles on cm3, up to 32 cycles on cm0
+		"subs.n	%[cyc], %[cyc], %[ovhd] \n\t"	// subtract the overhead in ns from the input:          1 cycle
+	"1:  subs.n	%[cyc], %[cyc], %[dnpl] \n\t"	// subtract the ns per loop from the input:             1 cycle
+		"bpl.n	1b"								// keep doing that while result is still positive:      2 cycles (when taken)
+	: [cyc] "=l" (cycles) : "0" (ns), [dnpl] "l" (platform::delay_ns_per_loop), [ovhd] "l" (2));
+}
+
+}
+
+void run_delay_inl(uint32_t ns)
+{
+	__DSB(); __ISB();
+	GpioA4::toggle();
+	const uint32_t start = DWT->CYCCNT;
+	modm::delay_ns_inl(ns);
+	const uint32_t stop = DWT->CYCCNT;
+	GpioA4::toggle();
+	const uint32_t cycles = (stop - start);
+	const uint32_t expected = uint64_t(SystemCoreClock) * ns / 1'000'000'000ull;
+	const uint32_t real = cycles * 1'000'000'000ull / SystemCoreClock;
+	MODM_LOG_INFO.printf("%7lu |  %5lu |  %5lu | %7lu      %c\n",
+	                     ns, expected, cycles, real, (cycles < (expected*1.1f) ? ' ' : 'x')) << modm::flush;
+}
+
+void run_delay(uint32_t ns)
+{
+	__DSB(); __ISB();
+	GpioA4::toggle();
+	const uint32_t start = DWT->CYCCNT;
+	modm::delay_ns(ns);
+	const uint32_t stop = DWT->CYCCNT;
+	GpioA4::toggle();
+	const uint32_t cycles = (stop - start);
+	const uint32_t expected = uint64_t(SystemCoreClock) * ns / 1'000'000'000ull;
+	const uint32_t real = cycles * 1'000'000'000ull / SystemCoreClock;
+	MODM_LOG_INFO.printf("%7lu |  %5lu |  %5lu | %7lu      %c\n",
+	                     ns, expected, cycles, real, (cycles < (expected*1.1f) ? ' ' : 'x')) << modm::flush;
+}
+
 int
 main()
 {
 	Board::initialize();
 	GpioA4::setOutput();
 
+	MODM_LOG_INFO << "\n\ndelay_ns in RAM, 3 cycles per loop\n\n";
+	MODM_LOG_INFO << "  delay | expect | cycles |   real \n";
+
+	run_delay(1);
+	run_delay(5);
+	run_delay(10);
+	run_delay(50);
+	run_delay(100);
+	run_delay(200);
+	run_delay(400);
+	run_delay(600);
+	run_delay(800);
+	run_delay(1000);
+	run_delay(1500);
+	run_delay(2000);
+	run_delay(10'000);
+	run_delay(100'000);
+	run_delay(1'000'000);
+
+	MODM_LOG_INFO << "\n\ndelay_ns inlined in Flash, 6 cycles per loop\n\n";
+	MODM_LOG_INFO << "  delay | expect | cycles |   real \n";
+	modm::platform::delay_ns_per_loop = std::round(6000/64);
+
+	run_delay_inl(1);
+	run_delay_inl(5);
+	run_delay_inl(10);
+	run_delay_inl(50);
+	run_delay_inl(100);
+	run_delay_inl(200);
+	run_delay_inl(400);
+	run_delay_inl(600);
+	run_delay_inl(800);
+	run_delay_inl(1000);
+	run_delay_inl(1500);
+	run_delay_inl(2000);
+	run_delay_inl(10'000);
+	run_delay_inl(100'000);
+	run_delay_inl(1'000'000);
+
 	while (true)
 	{
-		GpioA4::toggle();
-		modm::delay_ns(100000);
 	}
 
 	return 0;