FCode Memory Allocation

C

For OpenBoot 2

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

To map in portions of your device for ordinary access, use " map-in" $call-parent ( adr space size -- virt ), 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 ( virt size -- ), 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  ( n -- virt )  " dma-alloc" $call-parent  ;  
  : dma-free  ( virt n -- )    " dma-free" $call-parent  ;  
  : dma-map-in  ( virt n cache? -- devaddr )  " dma-map-in" $call-parent  ;  
  : dma-map-out  ( virt devaddr n -- )       " 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:

  · dma-alloc
  · 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.

Wait for DMA complete status.
Repeat DMA as needed, then perform dma-sync

Repeat steps 2 and 3 as needed
5) Deallocate the region when completed, with:

· dma-map-out
· dma-free

For OpenBoot 1

To obtain general-purpose memory, use buffer: or alloc-mem for small amounts (less than several hundred bytes). Use dma-alloc for larger amounts.

Use free-mem to deallocate memory allocated with alloc-mem. Use free-virtual to deallocate memory allocated with dma-alloc.

To map in portions of your device for ordinary access, use map-sbus.

To map out portions of your device, use free-virtual.

To use a region of system memory for DMA (for example, both direct CPU access and DMA access from a device), map it in with dma-alloc. CPU accesses and DMA accesses may be performed interchangeably.

When the memory is no longer needed, unmap it with free-virtual.

When unmapping multiple regions using free-virtual, you must perform the unmapping in the reverse order that the memory was originally mapped in.