esp32s3: correct clock frequencies

Author: cjpeterson

src/machine/machine_esp32s3.go

@@ -11,12 +11,54 @@ import (
 
 const deviceName = esp.Device
 
-const peripheralClock = 40_000000 // 80MHz
+const xtalClock = 40_000000       // 40MHz
+const apbClock = 80_000000        // 80MHz
+const cryptoPWMClock = 160_000000 // 160MHz
+
+// GetCPUFrequency returns the current CPU frequency of the chip.
+func GetCPUFrequency() (uint32, error) {
+	switch esp.SYSTEM.GetSYSCLK_CONF_SOC_CLK_SEL() {
+	case 0:
+		return xtalClock / (esp.SYSTEM.GetSYSCLK_CONF_PRE_DIV_CNT() + 1), nil
+	case 1:
+		switch esp.SYSTEM.GetCPU_PER_CONF_CPUPERIOD_SEL() {
+		case 0:
+			return 80e6, nil
+		case 1:
+			return 160e6, nil
+		case 2:
+			// If esp.SYSTEM.GetCPU_PER_CONF_PLL_FREQ_SEL() == 1, this is undefined
+			return 240e6, nil
+		}
+	case 2:
+		//RC Fast Clock
+		return (175e5) / (esp.SYSTEM.GetSYSCLK_CONF_PRE_DIV_CNT() + 1), nil
+	}
+	return 0, errors.New("machine: Unable to determine current cpu frequency")
+}
 
-// CPUFrequency returns the current CPU frequency of the chip.
-// Currently it is a fixed frequency but it may allow changing in the future.
-func CPUFrequency() uint32 {
-	return 160e6 // 80 MHz
+// SetCPUFrequency sets the frequency of the CPU to one of several targets
+func SetCPUFrequency(frequency uint32) error {
+	// Always assume we are on PLL. Lower frequencies can be set with a different
+	// clock source, but this will change the behavior of APB clock and Crypto PWM
+	// clock
+	//esp.SYSTEM.SetSYSCLK_CONF_SOC_CLK_SEL(1)
+	
+	switch frequency {
+	case 80_000000:
+		esp.SYSTEM.SetCPU_PER_CONF_CPUPERIOD_SEL(0)
+		esp.SYSTEM.SetCPU_PER_CONF_PLL_FREQ_SEL(0) // Reduce PLL freq when possible
+		return nil
+	case 160_000000:
+		esp.SYSTEM.SetCPU_PER_CONF_CPUPERIOD_SEL(1)
+		esp.SYSTEM.SetCPU_PER_CONF_PLL_FREQ_SEL(0)
+		return nil
+	case 240_000000:
+		esp.SYSTEM.SetCPU_PER_CONF_PLL_FREQ_SEL(1) // Increase PLL freq when needed
+		esp.SYSTEM.SetCPU_PER_CONF_CPUPERIOD_SEL(2)
+		return nil
+	}
+	return errors.New("machine: Unsupported CPU frequency selected. Supported: 80, 160, 240 MHz")
 }
 
 var (
@@ -188,7 +230,8 @@ func (uart *UART) Configure(config UARTConfig) {
 	if config.BaudRate == 0 {
 		config.BaudRate = 115200
 	}
-	uart.Bus.CLKDIV.Set(peripheralClock / config.BaudRate)
+	// Crystal clock source is selected by default
+	uart.Bus.CLKDIV.Set(xtalClock / config.BaudRate)
 }
 
 func (uart *UART) writeByte(b byte) error {

src/runtime/runtime_esp32s3.go

@@ -15,7 +15,7 @@ func main() {
 	// * 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
+	// * 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.
@@ -42,16 +42,15 @@ func main() {
 	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.SYSCLK_CONF.Set(1 << esp.SYSTEM_SYSCLK_CONF_SOC_CLK_SEL_Pos)
+	// 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 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)
+	// 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).
+	esp.SYSTEM.SetCPU_PER_CONF_PLL_FREQ_SEL(1)
+	esp.SYSTEM.SetCPU_PER_CONF_CPUPERIOD_SEL(2)
 
 	clearbss()