dma_mapalloc(D3X)dma_mapalloc(D3X)NAMEdma_mapalloc - allocate a DMA map
SYNOPSIS
#include "sys/types.h"
#include "sys/sema.h"
#include "sys/dmamap.h"
dmamap_t *dma_mapalloc(int type,int adapter, int num_pages,int flags);
Arguments
type Must be either DMA_A32VME or DMA_A24VME depending on the transfer
desired. (The DMA_SCSI type is reserved for exclusive use by the
SCSI host adapter driver.)
adapter
Specifies the I/O adapter to use for setting up the mapping This
should be set to the I/O bus adapter number to which the device
doing DMA is attached to.
num_pages
Specifies the maximum number of mapping registers to allocate.
Mapping registers are responsible for translating the addresses that
appear on the I/O bus to a format that could be used internally
within a system. On current Silicon Graphics systems, each mapping
register is capable of mapping a page of length 4096 bytes on the
I/O bus to a set of consecutive addresses on system memory. This is
true regardless of the system page size. The number of bytes each
mapping register is capable of mapping could change in future
systems. In order to keep the device driver platform independent,
use of the macro io_btoc is recommended to calculate the num_pages
parameter for required length of mapping. You need to allocate an
extra page for non-page aligned transfers-for example, a transfer of
4096 bytes starting at a non-aligned address actually requires two
mapping registers.
flags
Reserved for future development. For now, you should always set it
to 0.
DESCRIPTIONdma_mapalloc allocates DMA mapping registers on multiprocessor models and
returns a pointer to a structure, of type dmamap_t, for later use by the
mapping routine dma_map. You need DMA maps to access main memory through
VME A24 space. In addition, because DMA maps give you the ability to
perform transfers to non-contiguous physical memory, you also want them
for A32 access.
Use dma_mapfree to free the DMA mapping registers and other resources
associated with a given map.
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dma_mapalloc(D3X)dma_mapalloc(D3X)
VME adapter number to which a device is attached is available at edtinit
time via e_adap field in edt structure. It is also possible to get this
number by using the function vme_adapter(D3X).
This call can block (it calls psema) if no maps are available, so it must
never be called at interrupt time.
On Challenge and Onyx systems, the maximum amount of address space that
can be mapped for DMA by A32 VME devices is 64MB by default. This can be
changed by modifying the systune variable nvme32_dma. The value of
nvme32_dma is the maximum amount of address space (in megabytes) that may
be allocated for A32 VME devices. The default value for nvme32_dma is 64
(corresponding to the standard limit of 64MB of address space).
nvme32_dma must be a power of 2 and may not exceed 512 (meaning 512MB).
If a value larger than 512 is specified, it will be forced back down to
512. If the value is not a power of 2, it will be rounded up to the next
higher power of 2 (but not to exceed 512).
Return Values
dma_mapalloc returns a pointer to the DMA map structure on models that
support DMA maps. On other models, dma_mapalloc returns -1 to indicate
that DMA mapping is not possible on that model.
See Also
dma_map(D3X), dma_mapaddr(D3X), dma_mapfree(D3X), vme_adapter(D3X).
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