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NAME
- CachePreDMA
-
Take actions prior to hardware DMA (V37)
SYNOPSIS
paddress = CachePreDMA(vaddress,&length,flags)
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APTR CachePreDMA(APTR,LONG *,ULONG);
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APTR CachePreDMA(APTR,LONG *,ULONG);
FUNCTION
Take all appropriate steps before Direct Memory Access (DMA). This function is primarily intended for writers of DMA device drivers. The action will depend on the CPU type installed, caching modes, and the state of any Memory Management Unit (MMU) activity.
This function supports advanced cache architectures that have "copyback" modes. With copyback, write data may be cached, but not actually flushed out to memory. If the CPU has unflushed data at the time of DMA, data may be lost.
This function supports advanced cache architectures that have "copyback" modes. With copyback, write data may be cached, but not actually flushed out to memory. If the CPU has unflushed data at the time of DMA, data may be lost.
As implemented
68000 - Do nothing
68010 - Do nothing
68020 - Do nothing
68030 - Do nothing
68040 - Write any matching dirty cache lines back to memory.
????? - External cache boards, Virtual Memory Systems, or
68010 - Do nothing
68020 - Do nothing
68030 - Do nothing
68040 - Write any matching dirty cache lines back to memory.
As a side effect of the 68040's design, matching data
cache lines are also invalidated. Future CPUs may
be different.
cache lines are also invalidated. Future CPUs may
be different.
future hardware may patch this vector to best emulate
the intended behavior.
With a Bus-Snooping CPU, this function my end up
doing nothing.
the intended behavior.
With a Bus-Snooping CPU, this function my end up
doing nothing.
INPUTS
- address
-
Base address to start the action.
- length
-
Pointer to a longword with a length.
- flags
-
Values: DMA_Continue - Indicates this call is to complete
a prior request that was broken up.
- DMA_ReadFromRAM
-
Indicates that this DMA is a read from RAM to the DMA device (ie - a write to the hard drive) This flag is not required but if used must match in both the PreDMA and PostDMA calls. This flag *should* be used to help the system provide the best performance. This flag is safe in all versions of CachePreDMA()
RESULT
- paddress
-
Physical address that corresponds to the input virtual address.
- length
-
This length value will be updated to reflect the contiguous length of physical memory present at paddress. This may be smaller than the requested length. To get the mapping for the next chunk of memory, call the function again with a new address, length, and the DMA_Continue flag.
NOTES
Due to processor granularity, areas outside of the address range may be affected by the cache flushing actions. Care has been taken to ensure that no harm is done outside the range, and that activities on overlapping cache lines won't harm data.