B FCode Memory Allocation

To get general-purpose memory, use buffer: or alloc-mem. Use free-mem to de-allocate memory obtained with alloc-mem.

To map in portions of your SBus device for ordinary access use " map-in" $call-parent as in:

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my-address offset  my-space  size  " map-in" $call-parent  ( virt )

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To later map out those portions of your device, use " map-out" $call-parent as in:

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( virt )  size  " map-out" $call-parent

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To use a region of system memory for DMA (for example, for both direct CPU access and DMA access from a device), first define the following mapping and allocation routines, then follow the steps below to ensure data coherency.

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: dma-alloc  ( size -- virt )  " dma-alloc" $call-parent  ;
: dma-free   ( virt size -- )  " dma-free" $call-parent  ;
: dma-map-in  ( virt size cache? -- devaddr )
   " dma-map-in" $call-parent
;
: dma-map-out  ( virt devaddr size -- )  " dma-map-out" $call-parent  ;
: dma-sync  ( virt devaddr size -- )  \ Correct even if "dma-sync" missing
   " dma-sync" ['] $call-parent catch  if
      2drop 3drop
   then
;

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1. Allocate the DMA region with:

a. dma-alloc

b. dma-map-in

2. CPU accesses the region using virt from dma-alloc, then perform
dma-sync.

3. Start DMA operation, using devaddr from dma-map-in.

a. Wait for DMA complete status.

b. Repeat DMA as needed, then perform dma-sync

4. Repeat Steps 2 and 3 as needed

5. Deallocate the region when completed, with:

a. dma-map-out

b. dma-free