Problem getting alpha blending to work with layers


I am trying to get alpha blending to work with layers, on a Coral-P
board (Rev 4.0). The code has two layers, both with rectangles, and
they overlap somewhat. This is the code I use to attempt to get the
layer to have a uniform transparency over its entire surface:

PgLayerAlpha_t alpha;
alpha.salpha = 0x80;
alpha.dalpha = 0x80;

PgSetLayerArg(ellLayer, Pg_LAYER_ARG_ALPHA, &alpha,

I am successful in getting mulitple layers to display, and have
managed to get Chroma keying to work, but not alpha blending. Any
ideas? Also, for some reason the QNX API reports that the Coral-P
only supports these display modes:
8 (8 bit)
15 (15 bit)

and that the Coral-P supports these layer formats:
Layer 0:Pg_Layer_Format_ARGB1555
Layer 1:Pg_Layer_Format_ARGB1555
Layer 2:Pg_Layer_Format_ARGB1555, Pg_Layer_Format_PAL8
Layer 3:Pg_Layer_Format_ARGB1555, Pg_Layer_Format_PAL8
Layer 4:Pg_Layer_Format_ARGB1555, Pg_Layer_Format_PAL8,
Layer 5: Pg_Layer_Format_ARGB1555, Pg_Layer_Format_PAL8

Surely the Coral-P must support ARGB8888, otherwise how would you be
able to do alpha blending with 256 levels of transparency? Anybody
have any advice or code snippets?