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dma_relse(D3oddi)

dma_relse -- release previously allocated DMA channel

Synopsis

   #include <sys/dma.h>
   
   void dma_relse(unsigned chan);

Description

The dma_relse function releases a DMA channel that was previously allocated with the dma_alloc(D3oddi) or dma_start(D3oddi) function.

Arguments

chan

DMA channel to be released. Possible values are:

8-bit channels:: DMA_CH0, DMA_CH1, DMA_CH2, DMA_CH3
16-bit channels:: DMA_CH5, DMA_CH6, DMA_CH7

Channel 4 is not available. Other channels may be permanently allocated by system drivers. Consult the /usr/adm/messages file for a list of channels that are in use. Use the printcfg(D3oddi) function in your driver initialization routine to display the DMA channel that you select.

Return values

None.

Usage

This function should be called during the interrupt signaling completion of the DMA transfer or as soon as completion is detected (if polling is being used). If you intend to share DMA channels, you should use this routine. Sharing DMA channels is highly recommended.

If no dmareq structures are in the pending-request queue, dma_relse releases the channel, wakes up any processes sleeping on the channel, and exits. Otherwise it performs the next request on the queue by calling the routine defined in the xxd_proc member of the dmareq structure, with a pointer to the dmareq structure as a parameter. Because xxd_proc may be called during another driver's interrupt, the xxd_proc routine should be as minimal as possible to accomplish its task.

Context and synchronization

Non-blockable, interrupt, user, or blockable context.

Hardware applicability

All

Version applicability

oddi: 1, 2, 2mp, 3, 3mp, 4, 4mp, 5, 5mp, 6, 6mp

SVR5 DDI compatibility

This function is not supported for DDI drivers. See ``DMA'' in HDK Technical Reference for information about doing DMA operations in DDI drivers.

References

dma_enable(D3oddi), dma_start(D3oddi), dma_param(D3oddi), dma_alloc(D3oddi), dma_resid(D3oddi), printcfg(D3oddi)

Examples

The following example illustrates how to release a previously allocated channel:

   /* finished with DMA for now, release channel */
   	dma_relse( DMA_CH1 );