IOCTL_PWM_PIN_SET_POLARITY IOCTL (pwm.h)

Article
10/21/2021

Sets the signal polarity of the pin or channel. The control code sets the signal polarity based on a PWM_PIN_SET_POLARITY_INPUT structure. The signal polarity is either Active High or Active Low, as defined in the PWM_POLARITY enumeration.

Input buffer

A pointer to a buffer that contains a PWM_PIN_GET_POLARITY_OUTPUT structure. This represents the polarity value of the PWM controller, and is either Active High or Active Low.

Input buffer length

The size of the input buffer, in bytes.

Output buffer

Not used with this operation; set to NULL.

Output buffer length

Not used with this operation; set to zero.

Remarks

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL 
   WINAPI 
   DeviceIoControl( (HANDLE)       hDevice,         // handle to device
                    (DWORD)        IOCTL_PWM_PIN_SET_POLARITY, // dwIoControlCode(LPDWORD)      lpInBuffer,      // input buffer
                    (DWORD)        nInBufferSize,   // size of input buffer
                    (LPDWORD)      NULL,      // output buffer
                    (DWORD)        0,  // size of output buffer
                    (LPDWORD)      lpBytesReturned, // number of bytes returned
                    (LPOVERLAPPED) lpOverlapped );  // OVERLAPPED structure

Parameters	Description
hDevice [in]	A handle to the device. To obtain a device handle, call the CreateFile function.
dwIoControlCode [in]	The control code for the operation. Use IOCTL_PWM_PIN_SET_POLARITY for this operation.
lpInBuffer	A pointer to a buffer that contains a PWM_PIN_GET_POLARITY_OUTPUT structure. This represents the polarity value of the PWM controller, and is either Active High or Active Low.
nInBufferSize [in]	The size of the input buffer, in bytes.
lpOutBuffer [out]	Not used with this operation; set to NULL.
nOutBufferSize [in]	Not used with this operation; set to zero.
lpBytesReturned [out]	LPDWORD A pointer to a variable that receives the size of the data stored in the output buffer, in bytes. If the output buffer is too small, the call fails, GetLastError returns ERROR_INSUFFICIENT_BUFFER, and lpBytesReturned is zero. If lpOverlapped is NULL, lpBytesReturned cannot be NULL. Even when an operation returns no output data and lpOutBuffer is NULL, DeviceIoControl makes use of lpBytesReturned. After such an operation, the value of lpBytesReturned is meaningless. If lpOverlapped is not NULL, lpBytesReturned can be NULL. If this parameter is not NULL and the operation returns data, lpBytesReturned is meaningless until the overlapped operation has completed. To retrieve the number of bytes returned, call GetOverlappedResult. If the hDevice parameter is associated with an I/O completion port, you can retrieve the number of bytes returned by calling GetQueuedCompletionStatus.
lpOverlapped [in]	LPOVERLAPPED A pointer to an OVERLAPPED structure. If hDevice was opened without specifying FILE_FLAG_OVERLAPPED, lpOverlapped is ignored. If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, the operation is performed as an overlapped (asynchronous) operation. In this case, lpOverlapped must point to a valid OVERLAPPED structure that contains a handle to an event object. Otherwise, the function fails in unpredictable ways. For overlapped operations, DeviceIoControl returns immediately, and the event object is signaled when the operation has been completed. Otherwise, the function does not return until the operation has been completed or an error occurs.

Changing polarity is only allowed when the pin is stopped. You can tell whether the pin is stopped by using the IOCTL_PWM_PIN_IS_STARTED control code.

Changing polarity while a pin is started can lead to glitches on some Pulse Width Modulation (PWM) controllers. If you want to change polarity, stop the pin first, change the polarity, and then start the pin.

Requirements

Requirement	Value
Minimum supported client	Windows 10 [desktop apps only]
Minimum supported server	Windows Server 2016 [desktop apps only]
Header	pwm.h (include Pwm.h)

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