DMA_AllocateLogicalChannels (changes)
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DMAManager
» SWI Calls
» DMA_AllocateLogicalChannels
DMA_AllocateLogicalChannels
(SWI &46147)
| Entry | |
|---|---|
| R0 | Number of logical channels to allocate |
| Exit | |
|---|---|
| R0 | Number of first logical channel in allocation (any others are in a contiguous range above this number) |
| - | Other registers preserved |
Use
Since DMA controllers can now be added by third parties, a method of allocating logical channel numbers is required – this is what this SWI achieves. The logical channels are guaranteed to be unique within this session, even across reinitialisations of the DMAManager.
Notes
Currently DMAManager reserves logical channel numbers 0-&FFF (inclusive) for use by DMA controllers/drivers located in the HAL. Therefore DMA channels allocated by this SWI will start their numbering at &1000. However, this range may change in future in order to accommodate the requirements of individual HALs. Software outside the HAL should not make any assumptions about what range of logical channel numbers it will be allocated.
This documentation only covers the RISC OS 5 version of the DMAManager SWIs. For other OS versions, consult the appropriate PRM volume (e.g. volume 5a).
See also
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