Sunday, April 14, 2013

a320, first renders

A while back, I got my shiny new nexus4 in order to start playing with the new a320 adreno gpu.  It turns out, there are some quite significant changes in the new generation, in particular new shader ISA and all the registers around shader setup.  Other registers are mostly shuffled around, with a few new registers for new features (like MRT) and a few tweaks here and there.

There is quite a lot more flexibility in the shader ISA (thank-you opencl), and some nice changes like moving vertex fetch out of the shader and a lot more flexibility in the positioning of outputs/varyings.  Although as a result there was more that needed to be figured out to setup the shader related registers compared to a2xx.

At this point, I'm working with simple "fdre-a3xx" tests.  Basically libfdre (freedreno reverse engineering) gives a very simplified gl-ish API, with shaders written in assembly, rather than full on GLSL compiler.  I've got a pretty good shader assembler/disassembler, and cmdstream parsing utilizing envytools/librnn for parsing the register values.  There is still some more work to do at the fdre level (depth, stencil, textures) before work on the gallium driver can start, but things are progressing well.