OVMS3/OVMS.V3/components/duktape/config/feature-options/DUK_OPT_HEAPPTR16.yaml

34 lines
1.4 KiB
YAML

define: DUK_OPT_HEAPPTR16
introduced: 1.1.0
conflicts:
- DUK_OPT_DEBUG
related:
- DUK_OPT_HEAPPTR_ENC16
- DUK_OPT_HEAPPTR_DEC16
tags:
- lowmemory
- experimental
description: >
Enable "compression" of Duktape heap pointers into an unsigned 16-bit value.
Use together with DUK_OPT_HEAPPTR_ENC16 and DUK_OPT_HEAPPTR_DEC16.
Pointers compressed are those allocated from Duktape heap, using the user
provided allocation functions. Also NULL pointer must encode and decode
correctly.
Currently it is required that NULL encodes to integer 0, and integer
0 decodes to NULL. No other pointer can be encoded to 0.
This option reduces memory usage by several kilobytes, but has several
downsides. It can only be applied when Duktape heap is limited in size,
for instance, with 4-byte aligned allocations a 256kB heap (minus one value
for NULL) can be supported. Pointer encoding and decoding may be relatively
complicated as they need to correctly handle NULL pointers and
non-continuous memory maps used by some targets. The macro may need to call
out to a helper function in practice, which is much slower than an inline
implementation.
Current limitation: Duktape internal debug code enabled with e.g.
DUK_OPT_DEBUG and DUK_OPT_DPRINT doesn't have enough plumbing to be able to
decode pointers. Debug printing cannot currently be enabled when pointer
compression is active.