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PWM

This document describes the PWM module on the K3 secondary-core platform (ESOS/RTT), including its role, software architecture, device tree usage, and application programming model.

Module Overview​

PWM (Pulse Width Modulation) is used to generate pulse waveforms with configurable period and duty cycle. On the K3 ESOS secondary-core platform, the PWM module provides the following functions:

  • Enabling and disabling PWM output
  • Configuring the period and pulse width
  • Automatically probing and registering PWM devices through the DTS compatible property
  • Providing a unified PWM interface through the RT-Thread PWM device model
  • Working with the pinctrl subsystem to multiplex the PWM function onto the target PAD

On the current platform, PWM controllers use compatible strings from spacemit,k1x-rpwm0 through spacemit,k1x-rpwm9.

Software Architecture​

The following diagram illustrates the high-level call path from application or component driver code down to the hardware layer:

Application / component drivers
├─ rt_device_find("rpwm0")
├─ rt_pwm_set()
├─ rt_pwm_enable()
├─ rt_pwm_disable()
└─ rt_pwm_get()

                │
                ▼
RT-Thread PWM framework
├─ components/drivers/misc/rt_drv_pwm.c
└─ components/drivers/include/drivers/rt_drv_pwm.h

                │
                ▼
SoC PWM driver layer
└─ bsp/spacemit/drivers/pwm/pwm-pxa.c

                │
                ▼
PWM controller hardware
└─ rpwm0 ~ rpwm9

                │
                ▼
pinctrl / PAD multiplexing
└─ The PWM output PAD is selected through `pinctrl-0`

API Reference​

RT-Thread PWM API Overview​

When using the RT-Thread PWM interface, the PWM device handle is typically obtained by device name first:

  • rpwm0 ~ rpwm9: PWM device names on the K3 secondary-core platform

Register a PWM device

rt_err_t rt_device_pwm_register(struct rt_device_pwm *device,
                                const char *name,
                                const struct rt_pwm_ops *ops,
                                const void *user_data);

Parameters:

  • device: pointer to the PWM device object
  • name: device name, for example "rpwm0"
  • ops: PWM operation table
  • user_data: pointer to private user data

Return value:

  • RT_EOK: registration succeeded
  • other error codes: registration failed

Enable PWM output

rt_err_t rt_pwm_enable(struct rt_device_pwm *device, int channel);

Parameters:

  • device: PWM device handle
  • channel: PWM channel number

Return value:

  • RT_EOK: operation succeeded
  • other error codes: operation failed

Disable PWM output

rt_err_t rt_pwm_disable(struct rt_device_pwm *device, int channel);

Parameters:

  • device: PWM device handle
  • channel: PWM channel number

Return value:

  • RT_EOK: operation succeeded
  • other error codes: operation failed

Set the PWM period and pulse width

rt_err_t rt_pwm_set(struct rt_device_pwm *device,
                    int channel,
                    rt_uint32_t period,
                    rt_uint32_t pulse);

Parameters:

  • device: PWM device handle
  • channel: PWM channel number
  • period: PWM period (ns)
  • pulse: PWM pulse width (ns) and must satisfy pulse <= period

Return value:

  • RT_EOK: configuration succeeded
  • other error codes: configuration failed

PWM Control Commands​

Enable command

#define PWM_CMD_ENABLE      (128 + 0)

Description:

  • Enables PWM output

Return value:

  • None

Disable command

#define PWM_CMD_DISABLE     (128 + 1)

Description:

  • Disables PWM output

Return value:

  • None

Set command

#define PWM_CMD_SET         (128 + 2)

Description:

  • Sets the PWM period and pulse width

Return value:

  • None

Get command

#define PWM_CMD_GET         (128 + 3)

Description:

  • Retrieves the PWM configuration

Return value:

  • None

Usage Examples​

Device Tree Node Example​

&rpwm0 {
    pinctrl-names = "default";
    pinctrl-0 = <&rpwm0_0_cfg>;
    status = "okay";
};

Driver Usage Example​

struct rt_device_pwm *pwm_dev;

pwm_dev = (struct rt_device_pwm *)rt_device_find("rpwm0");
if (pwm_dev == RT_NULL)
    return -RT_ERROR;

rt_pwm_set(pwm_dev, 1, 100000, 50000);
rt_pwm_enable(pwm_dev, 1);

Disable Output Example​

rt_pwm_disable(pwm_dev, 1);

Shell Command Example​

pwm_set rpwm0 1 100000 50000
pwm_enable rpwm0 1