FCode Memory Allocation

B

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:

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

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

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

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.


  : 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  
  ;

Allocate the DMA region with:

a. dma-alloc
b. dma-map-in

CPU accesses the region using virt from dma-alloc, then perform dma-sync.
Start DMA operation, using devaddr from dma-map-in.
a. Wait for DMA complete status. b. Repeat DMA as needed, then perform dma-sync
Repeat Steps 2 and 3 as needed
Deallocate the region when completed, with:

a. dma-map-out
b. dma-free