GetShapeDmaNumFrames
Gets the number of Direct Memory Access (DMA) frames.Syntax
Parameters
context _In_Type: SHAPE_DMA_CONTEXT* Pointer to a SHAPE_DMA_CONTEXT structure.
Return value
Type: UINT32 Number of frames.Remarks
You can prevent blocked DMA commands by ensuring that your audio buffer is sufficiently large and that data is streamed at regular intervals (related to the buffer size). For example, if you are streaming four hardware frames at a time, ensure that some multiple of those frames (at least double-buffered at eight frames) are in the buffer so the hardware can write ahead of the title’s read pointer. Alternatively, you can enforce emptying of the buffer before submitting the next flowgraph (consume, update DMA read pointer, and then submit the flowgraph). For more details, see Blocked commands in Overview of SHAPE. The Direct Memory Access (DMA) system supports read and write functionality with automatic float-to-integer and integer-to-float conversion. The DMA system uses circular buffers containing de-interleaved samples in 128-sample blocks. The DMA processor allows the Scalable Hardware Audio Processing Engine (SHAPE) to send data from mix buffers to main system memory and retrieve data from main system into the mix buffers for further processing. DMA is done on a block basis, transferring one audio frame of data at a time. To facilitate block-interleaved data, a skip value specifies the number of audio frame blocks in system memory to skip (from the base address) when reading or writing samples. Multichannel streams therefore require one DMA context per channel. Audio data samples are always read and written as 32-bit values, either integer or float, as specified in thefloatConvert flag of the SHAPE_DMA_CONTEXT structure. Note that the direction of the DMA (read or write) is specified in the DMA command, not in the DMA context. This helps reduce the amount of data bandwidth. The DMA engine has no signal processing, but can perform float-to-integer conversion (or integer-to-float). This allows the application CPU to process data samples in floating-point format.
To calculate the size of a DMA buffer, use the following formula: