RSX

The RSX 'Reality Synthesizer' is a proprietary graphics processing unit (GPU) codeveloped by Nvidia and Sony for the PlayStation 3 game console. It is a GPU based on the Nvidia 7800GTX graphics processor and, according to Nvidia, is a G70/G71 (previously known as NV47) hybrid architecture with some modifications. The RSX has separate vertex and pixel shader pipelines. The GPU makes use of 256 MB GDDR3 RAM clocked at 650 MHz with an effective transmission rate of 1.4 GHz and up to 224 MB of the 3.2 GHz XDR main memory via the CPU (480 MB max). More features are revealed in the following chart delineating the differences between the RSX and the nVidia 7800 GTX. Note that the cache (Post Transform and Lighting Vertext Cache) is located between the vector shader and the triangle setup. A sample flow of data inside the RSX would see them first processed by 8 vertex shaders. The output are then sent to the 24 active pixel shaders, which can involve the 24 active texture units. Finally, the data is passed to the 8 Raster Operation Pipeline units (ROPs), and on out to the GDDR3. Note that the pixel shaders are grouped into groups of four (called Quads). There are 7 Quads, with 1 redundant, leaving 6 Quads active, which provides us with the 24 active pixel shaders listed above (6 times 4 equals 24). Since each Quad has 96kB of L1 and L2 cache, the total RSX texture cache is 576kB. General RSX features include 2x and 4x hardware anti-aliasing, and support for Shader Model 3.0. These SKUs have only been seen in consoles that had a Sony Refurbishment . Although the RSX has 256MB of GDDR3 RAM, not all of it is useable. The last 4MB is reserved for keeping track of the RSX internal state and issued commands. The 4MB of GPU Data contains RAMIN, RAMHT, RAMFC, DMA Objects, Graphic Objects, and the Graphic Context. The following is a breakdown of the address within 256MB of the RSX. Because of the aforementioned layout of the communication path between the different chips, and the latency and bandwidth differences between the various components, there are different access speeds depending on the direction of the access in relation to the source and destination. The following is a chart showing the speed of reads and writes to the GDDR3 and XDR memory from the viewpoint of the Cell and RSX. Note that these are measured speeds (rather than calculated speeds) and they should be worse if RSX and GDDR3 access are involved because these figures were measured when the RSX was clocked at 550Mhz and the GDDR3 memory was clocked at 700Mhz. The shipped PS3 has the RSX clocked in at 500Mhz (front and back end, although the pixel shaders run separately inside at 550Mhz). In addition, the GDDR3 memory was also clocked lower at 650Mhz. Because of the VERY slow Cell Read speed from the 256MB GDDR3 memory, it is more efficient for the Cell to work in XDR and then have the RSX pull data from XDR and write to GDDR3 for output to the HDMI display. This is why extra texture lookup instructions were included in the RSX to allow loading data from XDR memory (as opposed to the local GDDR3 memory).