...dW: The current way that the documentation seems to keep pointing to is that the SPE executable stuff is embedded within the ELF as a section. Is there any model development towards having the SPE executable as its own stand-alone file that can be read in by a framework application?
Chow: Yes, we do have that. We have a runtime environment that can take the SPU stand-alone executable as-is and run it on an SPU. We call such stand-alone SPU executable, SPUlet.
dW: Is that built on top of, like, the SPUFS model (See Resources) that was developed in Boeblingen?
Chow: SPUFS is a resource representation model that the kernel uses to manage SPU-related resources. Though the representation provides a clean boundary between what user-level applications can do and what kernel does, it is not convenient for an application programmer to use directly. Our additional runtime environment provides two different models for the Cell programmer. One is the SPUlet model. A programmer simply creates an SPU executable, and our runtime environment can load it to an SPU and start its execution. In this case, the SPU executable is a stand-alone file. It does not need to be included in a CESOF file. Another model is called SPE-thread model. It is also built on top of the SPUFS representation. A programmer using the whole Cell resource usually programs to this SPE-thread model that allows the programmer to manage more than one SPE program or thread. We use CESOF to piece together these different SPE programs and PPE programs into a single executable image.
dW: And another term that I noticed you used in your paper was "double-buffering." I'm aware of the use of the term "double-buffering" in video composition, but it is also the correct term in this application?
Chow: It is a term and technique frequently used by PS2 game programmers. Of course, there is a similar concept in video composition. Because the DMA engine and the CPU can operate independently, we start the data transfer of a new piece of data while we are processing the old piece of data. In the video composition term, we are drawing the next frame while we are showing the previous frame. A similar technique used by the MPI programming is called "prefetching."
dW: I see a lot of "mailboxes," references to input and output "mailboxes." Is that basically a DMA address?
Chow: No. The mailbox is a special set of registers of SPE and PPE. Each SPE can communicate with the PPE through these registers. A PU program can simply send or receive 32-bits data to and from SPU . It can be used as a very simple synchronization mechanism between PPU and SPU programs.
dW: Is it polled or interrupt-driven?
Chow: Both -- the architecture can support both...
