PWM Woes

Just in case anyone is having issues with the ESP8266 SDK and PWM. Problem now “solved” but you might find this interesting.

For many months now I’ve been using the PWM on the ESP8266 successfully, so much so that I’ve not tested it and just recently I’ve noticed it no longer works. Specifically, the PWM startup routine forces my ESP8266s to reboot with a watchdog timeout.

So first things first, the SDK manual appears to STILL be incorrect. It states in version 1.53 (ESP8266 SDK API guide) in page 178 that the DUTY parameter is pointer to an 8 bit array.

Yet the header and routines elsewhere require 32 bit values for the array. I’ve always ignored this.

#define PWM_1_OUT_IO_MUX PERIPHS_IO_MUX_MTDO_U
#define PWM_1_OUT_IO_NUM 15
#define PWM_1_OUT_IO_FUNC FUNC_GPIO15

#define PWM_3_OUT_IO_MUX PERIPHS_IO_MUX_GPIO4_U
#define PWM_3_OUT_IO_NUM 4
#define PWM_3_OUT_IO_FUNC FUNC_GPIO4

#define PWM_4_OUT_IO_MUX PERIPHS_IO_MUX_GPIO5_U
#define PWM_4_OUT_IO_NUM 5
#define PWM_4_OUT_IO_FUNC FUNC_GPIO5

uint32 duty[] = {0, 0, 0};
uint32 freq = 1000;
static uint8 donepwm = 0;

uint32 io_info[][3] = {
  {PWM_1_OUT_IO_MUX, PWM_1_OUT_IO_FUNC, PWM_1_OUT_IO_NUM},
  {PWM_3_OUT_IO_MUX, PWM_3_OUT_IO_FUNC, PWM_3_OUT_IO_NUM},
  {PWM_4_OUT_IO_MUX, PWM_4_OUT_IO_FUNC, PWM_4_OUT_IO_NUM}
};

So with these definitions I call….

if (donepwm == 0) {
   pwm_init(freq, duty, 3, io_info);
   donepwm = 1;
}

You should call the setup once only.. hence the wrapper using “donepwm”. This has always worked and yet now, no matter what I do, this crashes the processor – usually a few seconds after it has been called.

Result..

ets Jan  8 2013,rst cause:4, boot mode:(1,0)

wdt reset

This used to work – now it causes the WDT.

The example in the manual..

Example: uint32 io_info[][3] =  {{PWM_0_OUT_IO_MUX,PWM_0_OUT_IO_FUNC,PWM_0_OUT_IO_NUM},          {PWM_1_OUT_IO_MUX,PWM_1_OUT_IO_FUNC,PWM_1_OUT_IO_NUM}, {PWM_2_OUT_IO_MUX,PWM_2_OUT_IO_FUNC,PWM_2_OUT_IO_NUM}};

pwm_init(light_param.pwm_period, light_param.pwm_duty, 3, io_info);

HERE is a  “fix”…

http://www.esp8266.com/viewtopic.php?f=6&t=4675&p=46060#p46060

I amended the rom0.ld file and sure enough – fixed…

But that means there’s an issue somewhere –  and that manual needs fixing  – I hope Espressif are looking in.