runtime_esp32s3.go

//go:build esp32s3

package runtime

import (
	"device"
	"device/esp"
	"machine"
	"unsafe"
)

// This is the function called on startup after the flash (IROM/DROM) is
// initialized and the stack pointer has been set.
//
//export main
func main() {
	// This initialization configures the following things:
	// * It disables all watchdog timers. They might be useful at some point in
	//   the future, but will need integration into the scheduler. For now,
	//   they're all disabled.
	// * It sets the CPU frequency to 240MHz, which is the maximum speed allowed
	//   for this CPU. Lower frequencies might be possible in the future, but
	//   running fast and sleeping quickly is often also a good strategy to save
	//   power.
	// TODO: protect certain memory regions, especially the area below the stack
	// to protect against stack overflows. See
	// esp_cpu_configure_region_protection in ESP-IDF.

	// Disable RTC watchdog.
	esp.RTC_CNTL.WDTWPROTECT.Set(0x50D83AA1)
	esp.RTC_CNTL.WDTCONFIG0.Set(0)
	esp.RTC_CNTL.WDTWPROTECT.Set(0x0) // Re-enable write protect

	// Disable Timer 0 watchdog.
	esp.TIMG1.WDTWPROTECT.Set(0x50D83AA1) // write protect
	esp.TIMG1.WDTCONFIG0.Set(0)           // disable TG0 WDT
	esp.TIMG1.WDTWPROTECT.Set(0x0)        // Re-enable write protect

	esp.TIMG0.WDTWPROTECT.Set(0x50D83AA1) // write protect
	esp.TIMG0.WDTCONFIG0.Set(0)           // disable TG0 WDT
	esp.TIMG0.WDTWPROTECT.Set(0x0)        // Re-enable write protect

	// Disable super watchdog.
	esp.RTC_CNTL.SWD_WPROTECT.Set(0x8F1D312A)
	esp.RTC_CNTL.SWD_CONF.Set(esp.RTC_CNTL_SWD_CONF_SWD_DISABLE)
	esp.RTC_CNTL.SWD_WPROTECT.Set(0x0) // Re-enable write protect

	// Change CPU frequency from 20MHz to 80MHz, by switching from the XTAL to the
	// PLL clock source (see table "CPU Clock Frequency" in the reference manual).
	esp.SYSTEM.SetSYSCLK_CONF_SOC_CLK_SEL(1)

	// Change CPU frequency from 80MHz to 240MHz by setting SYSTEM_PLL_FREQ_SEL to
	// 1 and SYSTEM_CPUPERIOD_SEL to 2 (see table "CPU Clock Frequency" in the
	// reference manual).
	// We do this gradually to allow PLL and system to stabilize.
	esp.SYSTEM.SetCPU_PER_CONF_PLL_FREQ_SEL(1)

	// First switch to 160MHz (intermediate step)
	esp.SYSTEM.SetCPU_PER_CONF_CPUPERIOD_SEL(1)
	// Small delay to let PLL stabilize at 160MHz
	for i := 0; i < 1000; i++ {
		_ = esp.SYSTEM.CPU_PER_CONF.Get()
	}

	// Now switch to 240MHz
	esp.SYSTEM.SetCPU_PER_CONF_CPUPERIOD_SEL(2)
	// Small delay to let PLL stabilize at 240MHz
	for i := 0; i < 1000; i++ {
		_ = esp.SYSTEM.CPU_PER_CONF.Get()
	}

	// Clear bss. Repeat many times while we wait for cpu/clock to stabilize
	for x := 0; x < 30; x++ {
		clearbss()
	}

	// Initialize main system timer used for time.Now.
	initTimer()

	// Set up the Xtensa interrupt vector table.
	interruptInit()

	// Initialize the heap, call main.main, etc.
	run()

	// Fallback: if main ever returns, hang the CPU.
	exit(0)
}

func init() {
	// Initialize UART.
	machine.InitSerial()
}

func abort() {
	// lock up forever
	print("abort called\n")
}

// interruptInit installs the Xtensa vector table by writing its address
// to the VECBASE special register and ensures all CPU interrupts are
// initially disabled.
func interruptInit() {
	// Disable all CPU interrupts while we configure.
	device.AsmFull("wsr {zero}, INTENABLE", map[string]interface{}{
		"zero": uintptr(0),
	})

	// Write the vector table address to VECBASE (SR 231).
	vecbase := uintptr(unsafe.Pointer(&_vector_table))
	device.AsmFull("wsr {vecbase}, VECBASE", map[string]interface{}{
		"vecbase": vecbase,
	})

	// Synchronize pipeline after writing special registers.
	device.Asm("rsync")
}

//go:extern _vector_table
var _vector_table [0]uintptr

//go:extern _sbss
var _sbss [0]byte

//go:extern _ebss
var _ebss [0]byte