ESP32 ledc 1bit PWM Configuration is impossible

[mhuttner]

Board

ESP32

Device Description

ESP32-WROOM

Hardware Configuration

GPIO19 is LED PWM Pin

Version

v2.0.4

IDE Name

arduino-cli

Operating System

macOS 12.4

Flash frequency

40MHz

PSRAM enabled

no

Upload speed

921600

Description

ledcWrite makes it impossible to set the duty cycle to 50% for 1bit PWM because of this:

arduino-esp32/cores/esp32/esp32-hal-ledc.c

Lines 89 to 96 in 9432163

	//Fixing if all bits in resolution is set = LEDC FULL ON
	uint32_t max_duty = (1 << channels_resolution[chan]) - 1;
	if(duty == max_duty){
	duty = max_duty + 1;
	}
	ledc_set_duty(group, channel, duty);

when channels_resolution[chan] is 1 the possible duty cycles should be 0 (0%), 1 (50%) and 2(100%).
But for a duty of 1 max_duty will be 1 (1<<1 - 1) and since duty == max_duty the duty will be set to 2

Sketch

void setup() {
    uint8_t channel = 0;
    
    uint8_t bits = 1;
    uint8_t pin = 19;
    uint32_t freq = 40 * 1000 * 1000 // 40 MHz
    uint8_t duty = 1; // 50% duty

    ledcSetup(channel, freq, bits);
    ledcAttachPin(pin, channel);
    ledcWrite(channel, duty);
}

void loop(){}

Debug Message

None

Other Steps to Reproduce

No response

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[lbernstone]

1-bit PWM means the duty cycle is fixed at 50%. https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/ledc.html#supported-range-of-frequency-and-duty-resolutions

[mhuttner]

Yes, but i can not manage to configure it to get output on the pin.

Removing the ledcWrite(channel, duty);results in no output.
If i comment out

if(duty == max_duty){ 
     duty = max_duty + 1; 
 } 

the example above works as expected and i get a PWM Signal.

[P-R-O-C-H-Y]

Hi @mhuttner, this part of code was added, because of a simple reason. If all bits from given resolution are set, then LEDC should be full on.

Quick example is on 8-bit resolution. The value is between 0-255, thats 8 bits. But without this piece of code the 255 won't be 100% on, you need to write 256 to be fully on, but it makes no sense.
According to @lbernstone mentioned link, I will make a PR to change 1-bit resolution to be 0 - fully off and 1 be 50%. It makes sense.
With 1 bit you can never set duty to 0% , 50% and 100%. Thats 3 values, you have only 2 available (0/1).

If you need to be able to set these, select 2 bits resolution.
Example using only 2 bits:
0 - always low
1 -> actually sets to 1 - 25% duty
2 -> actually sets to 2 - 50% duty
3 -> actually sets to 4 - always high (100% duty)

With this change, we loose the value 1 for all resolutions, but for most use cases, it affordable price.

[P-R-O-C-H-Y]

@mhuttner Can you please test your code with this change:

    if((duty == max_duty) && (max_duty != 1)) {
        duty = max_duty + 1;
    }

Thanks!

[mhuttner]

@P-R-O-C-H-Y Thanks for the response. The change works with my code.