machine/esp32: add PWM support using the LEDC peripheral for classic esp32 board

make/smoketest.mk

@@ -477,6 +477,8 @@ ifneq ($(XTENSA), 0)
 	@$(MD5SUM) $(SMOKE_OUT).bin
 	$(TINYGO) build -size short -o $(SMOKE_OUT).bin -target=esp32-coreboard-v2  examples/adc
 	@$(MD5SUM) $(SMOKE_OUT).bin
+	$(TINYGO) build -size short -o $(SMOKE_OUT).bin -target=esp32-coreboard-v2  examples/pwm
+	@$(MD5SUM) $(SMOKE_OUT).bin
 	$(TINYGO) build -size short -o $(SMOKE_OUT).bin -target=esp32c3-generic     examples/machinetest
 	@$(MD5SUM) $(SMOKE_OUT).bin
 	$(TINYGO) build -size short -o $(SMOKE_OUT).bin -target=esp32s3-generic     examples/machinetest

src/examples/pwm/esp32-coreboard-v2.go

@@ -0,0 +1,11 @@
+//go:build esp32_coreboard_v2
+
+package main
+
+import "machine"
+
+var (
+	pwm  = machine.PWM0
+	pinA = machine.GPIO18
+	pinB = machine.GPIO19
+)

src/machine/machine_esp32_pwm.go

@@ -0,0 +1,141 @@
+//go:build esp32
+
+// PWM on the classic ESP32 uses the LEDC peripheral.
+//
+// LEDC here has two halves: a high-speed one and a low-speed one. This file uses
+// the high-speed half. It gives 4 timers (PWM0-PWM3) and 8 channels.
+//
+// The code that is the same on every ESP32 chip is in machine_esp32xx_pwm.go.
+// This file adds only the parts that are different here.
+//
+// Three things are different from the ESP32-C3 and the ESP32-S3:
+//
+//   - The clock is switched on in DPORT. The newer chips renamed that block to
+//     SYSTEM. This chip also has no LEDC.CONF_CLK_EN bit.
+//   - Register names start with HS, for example HSTIMER0_CONF and HSCH0_CONF0.
+//   - There is no PARA_UP bit. On the C3 and S3 you set PARA_UP to say "apply my
+//     changes now". Here the channel applies them by itself, at the end of the
+//     period it is in. That is what makes it "high speed".
+//
+// Register addresses and bit positions come from the ESP32 TRM, chapter 14
+// "LED PWM Controller", section 14.4 "Register Summary".
+
+package machine
+
+import (
+	"device/esp"
+	"runtime/volatile"
+	"unsafe"
+)
+
+// The GPIO matrix can send an internal signal to almost any pin. Each signal has
+// a number. High-speed LEDC channel 0 is number 71, and the rest follow on from
+// there, so channels 0 to 7 are 71 to 78.
+// (From Espressif's soc/gpio_sig_map.h: LEDC_HS_SIG_OUT0_IDX.)
+const LEDC_HS_SIG_OUT0_IDX = 71
+
+const ledcChannelsESP32 = 8
+
+// Each channel has 5 registers and each timer has 2, so the blocks repeat at a
+// fixed distance. HSCH0_CONF0 is at 0x0 and HSCH1_CONF0 is at 0x14.
+// HSTIMER0_CONF is at 0x140 and HSTIMER1_CONF is at 0x148.
+const (
+	ledcChannelStride = 0x14
+	ledcTimerStride   = 0x8
+)
+
+// Bit positions in HSCHn_CONF0, HSCHn_CONF1 and HSTIMERn_CONF.
+const (
+	ledcTimerSelPos  = 0       // CONF0, which timer the channel follows
+	ledcSigOutEn     = 1 << 2  // CONF0, let the channel drive the pin
+	ledcDutyCyclePos = 10      // CONF1
+	ledcDutyNumPos   = 20      // CONF1
+	ledcDutyInc      = 1 << 30 // CONF1
+	ledcDutyStart    = 1 << 31 // CONF1, apply the other CONF1 fields
+	ledcDivNumPos    = 5       // TIMER CONF, clock divider
+	ledcTimerRst     = 1 << 24 // TIMER CONF
+	ledcTickSelAPB   = 1 << 25 // TIMER CONF, 1 is APB_CLK and 0 is REF_TICK
+)
+
+var (
+	PWM0 = &LEDCPWM{SigOutBase: LEDC_HS_SIG_OUT0_IDX, NumChannels: ledcChannelsESP32, timerNum: 0}
+	PWM1 = &LEDCPWM{SigOutBase: LEDC_HS_SIG_OUT0_IDX, NumChannels: ledcChannelsESP32, timerNum: 1}
+	PWM2 = &LEDCPWM{SigOutBase: LEDC_HS_SIG_OUT0_IDX, NumChannels: ledcChannelsESP32, timerNum: 2}
+	PWM3 = &LEDCPWM{SigOutBase: LEDC_HS_SIG_OUT0_IDX, NumChannels: ledcChannelsESP32, timerNum: 3}
+)
+
+// chanReg returns a register of channel ch, given the register of channel 0.
+func chanReg(channel0 *volatile.Register32, ch uint8) *volatile.Register32 {
+	return (*volatile.Register32)(unsafe.Add(unsafe.Pointer(channel0), uintptr(ch)*ledcChannelStride))
+}
+
+// timerReg returns a register of timer t, given the register of timer 0.
+func timerReg(timer0 *volatile.Register32, t uint8) *volatile.Register32 {
+	return (*volatile.Register32)(unsafe.Add(unsafe.Pointer(timer0), uintptr(t)*ledcTimerStride))
+}
+
+// enableClock turns the LEDC hardware on and picks its clock.
+func (pwm *LEDCPWM) enableClock() {
+	// Every peripheral starts switched off, to save power. These registers are
+	// in DPORT on this chip. The C3 and S3 call the same block SYSTEM.
+	if !ledcStarted {
+		esp.DPORT.SetPERIP_CLK_EN_LEDC_CLK_EN(1)
+		esp.DPORT.SetPERIP_RST_EN_LEDC_RST(1)
+		esp.DPORT.SetPERIP_RST_EN_LEDC_RST(0)
+		ledcStarted = true
+	}
+
+	// Use APB_CLK, which runs at 80MHz. This chip has no CONF_CLK_EN bit, so
+	// there is nothing more to switch on.
+	esp.LEDC.SetCONF_APB_CLK_SEL(1)
+}
+
+// setTimerConf writes the resolution and the divider that Configure worked out
+// into one timer.
+//
+// Watch TICK_SEL. It is 1 here, not 0. On this chip:
+//
+//	1 = APB_CLK, 80MHz   <- what we want
+//	0 = REF_TICK, 1MHz
+//
+// The low speed timers on the C3 and S3 use the opposite meaning, so their code
+// writes 0. Writing 0 here would make every frequency 80 times too slow.
+//
+// These timers have no PARA_UP bit. The short reset pulse at the end is what
+// makes the new values take effect.
+func (pwm *LEDCPWM) setTimerConf(dutyRes uint8, divReg uint32) {
+	conf := timerReg(&esp.LEDC.HSTIMER0_CONF, pwm.timerNum)
+	value := uint32(dutyRes) | divReg<<ledcDivNumPos | ledcTickSelAPB
+	conf.Set(value | ledcTimerRst)
+	conf.Set(value)
+}
+
+// chanDisable stops a channel from driving its pin.
+func chanDisable(ch uint8) {
+	chanReg(&esp.LEDC.HSCH0_CONF0, ch).ClearBits(ledcSigOutEn)
+}
+
+// chanOp does the work for one channel, numbered 0 to 7. It either sets the
+// channel up or changes its duty.
+//
+// DUTY_SCALE stays 0. LEDC can fade slowly from one duty to the next, and 0
+// turns that off, so the duty changes in a single step.
+func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32) {
+	conf0 := chanReg(&esp.LEDC.HSCH0_CONF0, ch)
+
+	// DUTY_NUM and DUTY_CYCLE are 1 step of 1 period, which is the smallest
+	// fade. With DUTY_SCALE at 0 the step size is 0, so no fade happens.
+	const conf1 = 1<<ledcDutyCyclePos | 1<<ledcDutyNumPos | ledcDutyInc | ledcDutyStart
+
+	switch op {
+	case ledcChanOpInit:
+		chanReg(&esp.LEDC.HSCH0_HPOINT, ch).Set(0)
+		chanReg(&esp.LEDC.HSCH0_DUTY, ch).Set(0)
+		chanReg(&esp.LEDC.HSCH0_CONF1, ch).Set(conf1)
+		conf0.Set(uint32(pwm.timerNum)<<ledcTimerSelPos | ledcSigOutEn)
+	case ledcChanOpSetDuty:
+		chanReg(&esp.LEDC.HSCH0_DUTY, ch).Set(duty)
+		chanReg(&esp.LEDC.HSCH0_CONF1, ch).Set(conf1)
+		conf0.SetBits(ledcSigOutEn)
+	}
+}

src/machine/machine_esp32c3_pwm.go

@@ -23,12 +23,32 @@ var (
 	PWM3 = &LEDCPWM{SigOutBase: LEDC_LS_SIG_OUT0_IDX, NumChannels: ledcChannelsC3, timerNum: 3}
 )
 
-// chanOp implements LEDC low-speed channel ops for ESP32-C3 (channels 0–5 only).
-func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool) {
-	invVal := uint32(0)
-	if inverting {
-		invVal = 1
+// chanDisable stops a channel from driving its pin.
+func chanDisable(ch uint8) {
+	switch ch {
+	case 0:
+		esp.LEDC.SetCH0_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH0_CONF0_PARA_UP(1)
+	case 1:
+		esp.LEDC.SetCH1_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH1_CONF0_PARA_UP(1)
+	case 2:
+		esp.LEDC.SetCH2_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH2_CONF0_PARA_UP(1)
+	case 3:
+		esp.LEDC.SetCH3_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH3_CONF0_PARA_UP(1)
+	case 4:
+		esp.LEDC.SetCH4_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH4_CONF0_PARA_UP(1)
+	case 5:
+		esp.LEDC.SetCH5_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH5_CONF0_PARA_UP(1)
 	}
+}
+
+// chanOp implements LEDC low-speed channel ops for ESP32-C3 (channels 0–5 only).
+func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32) {
 	switch ch {
 	case 0:
 		switch op {
@@ -51,8 +71,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH0_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH0_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH0_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH0_CONF0_IDLE_LV(invVal)
 		}
 	case 1:
 		switch op {
@@ -75,8 +93,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH1_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH1_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH1_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH1_CONF0_IDLE_LV(invVal)
 		}
 	case 2:
 		switch op {
@@ -99,8 +115,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH2_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH2_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH2_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH2_CONF0_IDLE_LV(invVal)
 		}
 	case 3:
 		switch op {
@@ -123,8 +137,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH3_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH3_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH3_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH3_CONF0_IDLE_LV(invVal)
 		}
 	case 4:
 		switch op {
@@ -147,8 +159,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH4_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH4_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH4_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH4_CONF0_IDLE_LV(invVal)
 		}
 	case 5:
 		switch op {
@@ -171,8 +181,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH5_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH5_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH5_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH5_CONF0_IDLE_LV(invVal)
 		}
 	}
 }

src/machine/machine_esp32s3_pwm.go

@@ -23,12 +23,38 @@ var (
 	PWM3 = &LEDCPWM{SigOutBase: LEDC_LS_SIG_OUT0_IDX, NumChannels: ledcChannelsS3, timerNum: 3}
 )
 
-// chanOp implements LEDC low-speed channel ops for ESP32-S3 (channels 0–7).
-func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool) {
-	invVal := uint32(0)
-	if inverting {
-		invVal = 1
+// chanDisable stops a channel from driving its pin.
+func chanDisable(ch uint8) {
+	switch ch {
+	case 0:
+		esp.LEDC.SetCH0_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH0_CONF0_PARA_UP(1)
+	case 1:
+		esp.LEDC.SetCH1_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH1_CONF0_PARA_UP(1)
+	case 2:
+		esp.LEDC.SetCH2_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH2_CONF0_PARA_UP(1)
+	case 3:
+		esp.LEDC.SetCH3_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH3_CONF0_PARA_UP(1)
+	case 4:
+		esp.LEDC.SetCH4_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH4_CONF0_PARA_UP(1)
+	case 5:
+		esp.LEDC.SetCH5_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH5_CONF0_PARA_UP(1)
+	case 6:
+		esp.LEDC.SetCH6_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH6_CONF0_PARA_UP(1)
+	case 7:
+		esp.LEDC.SetCH7_CONF0_SIG_OUT_EN(0)
+		esp.LEDC.SetCH7_CONF0_PARA_UP(1)
 	}
+}
+
+// chanOp implements LEDC low-speed channel ops for ESP32-S3 (channels 0–7).
+func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32) {
 	switch ch {
 	case 0:
 		switch op {
@@ -51,8 +77,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH0_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH0_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH0_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH0_CONF0_IDLE_LV(invVal)
 		}
 	case 1:
 		switch op {
@@ -75,8 +99,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH1_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH1_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH1_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH1_CONF0_IDLE_LV(invVal)
 		}
 	case 2:
 		switch op {
@@ -99,8 +121,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH2_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH2_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH2_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH2_CONF0_IDLE_LV(invVal)
 		}
 	case 3:
 		switch op {
@@ -123,8 +143,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH3_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH3_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH3_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH3_CONF0_IDLE_LV(invVal)
 		}
 	case 4:
 		switch op {
@@ -147,8 +165,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH4_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH4_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH4_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH4_CONF0_IDLE_LV(invVal)
 		}
 	case 5:
 		switch op {
@@ -171,8 +187,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH5_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH5_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH5_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH5_CONF0_IDLE_LV(invVal)
 		}
 	case 6:
 		switch op {
@@ -195,8 +209,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH6_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH6_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH6_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH6_CONF0_IDLE_LV(invVal)
 		}
 	case 7:
 		switch op {
@@ -219,8 +231,6 @@ func (pwm *LEDCPWM) chanOp(ch uint8, op ledcChanOp, duty uint32, inverting bool)
 			esp.LEDC.SetCH7_CONF1_DUTY_START(1)
 			esp.LEDC.SetCH7_CONF0_SIG_OUT_EN(1)
 			esp.LEDC.SetCH7_CONF0_PARA_UP(1)
-		case ledcChanOpSetInvert:
-			esp.LEDC.SetCH7_CONF0_IDLE_LV(invVal)
 		}
 	}
 }