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// +build esp32c3
package runtime
import (
"device/esp"
"device/riscv"
)
// 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 160MHz, 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 Timer 0 watchdog.
esp.TIMG0.WDTCONFIG0.Set(0)
// Disable RTC watchdog.
esp.RTC_CNTL.RTC_WDTWPROTECT.Set(0x50D83AA1)
esp.RTC_CNTL.RTC_WDTCONFIG0.Set(0)
// Disable super watchdog.
esp.RTC_CNTL.RTC_SWD_WPROTECT.Set(0x8F1D312A)
esp.RTC_CNTL.RTC_SWD_CONF.Set(esp.RTC_CNTL_RTC_SWD_CONF_SWD_DISABLE)
// 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.SYSCLK_CONF.Set(1 << esp.SYSTEM_SYSCLK_CONF_SOC_CLK_SEL_Pos)
// Change CPU frequency from 80MHz to 160MHz by setting SYSTEM_CPUPERIOD_SEL
// to 1 (see table "CPU Clock Frequency" in the reference manual).
// Note: we might not want to set SYSTEM_CPU_WAIT_MODE_FORCE_ON to save
// power. It is set here to keep the default on reset.
esp.SYSTEM.CPU_PER_CONF.Set(esp.SYSTEM_CPU_PER_CONF_CPU_WAIT_MODE_FORCE_ON | esp.SYSTEM_CPU_PER_CONF_PLL_FREQ_SEL | 1<<esp.SYSTEM_CPU_PER_CONF_CPUPERIOD_SEL_Pos)
clearbss()
// Initialize main system timer used for time.Now.
initTimer()
// Initialize the heap, call main.main, etc.
run()
// Fallback: if main ever returns, hang the CPU.
abort()
}
func abort() {
// lock up forever
for {
riscv.Asm("wfi")
}
}
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