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 Posted:
Fri Sep 09, 2005 11:31 pm Post subject:
new -technical- info about Xbox360 [tech-heads only apply] |
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credit to 'One' on the Beyond3D console forum for this:
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Zenji Nishikawa and Hiroshige Goto have uploaded their reports about the
Xbox 360 session at CEDEC 2005 in Tokyo as they could somehow get permission
to publish what they heard at the NDA-based session.
Zenji Nishikawa article @ Mycom PC Web (6 pages article)
http://pcweb.mycom.co.jp/articles/2005/09/09/cedec1/
Hiroshige Goto article @ Impress PC Watch
http://pc.watch.impress.co.jp/docs/...9/kaigai210.htm
Goto's main focus is on Xbox 360 CPU and the comparison with Cell PPE with
their pipeline diagrams (PPE's contains many guesswork by him). His
conclusion is just they are very alike, though the pipeline length is
different between these 2 and the organization of the PPE vector/scalar
pipelines are unknown. Anyway it seems it doesn't give us a clue about the
recent Crytek comment about Xbox 360 CPU/PPE.
While Goto does interesting speculation as always, Nishikawa does
fact-oriented, very detailed report and description about the session.
Here's a summary of revelations/semi-revelations that could be gleaned from
those 2 article about Xbox 360:
+ Among 3 cores in Xbox 360 CPU (codenamed "PX"), Core 0 is primary and
Core 1/2 are secondary. Core 0 is fully usable by a game program. Core 1 and
Core 2 are shared by a game program and the Xbox 360 system. Network stacks,
services, drivers such as a USB driver run on those secondary cores. 5%
computation usage of both core 1 and core 2 are reserved by the system.
+ The XMA (modified WMAPro) decoder in the southbridge chip can decode 256
XMA channels at the same time. Though the compression rate is variable, 1/8
is just enough for typical usage. After decoding, all software sound
processing (multi-channel mixing, 3D surround sound, Dolby Pro Logic
II/Dolby Digital 5.1 encoding) are done on CPU Core 2. When it processes 256
channels at the same time it costs 25% load of Core 2.
+ A hardware-assisted tile-rendering method called 'Predicated Tiling' is
supplied as a library for Xbox 360 for the case when 10MB eDRAM is not
sufficient, for example 64bit (FP16 * RGBA) HDR rendering + Z buffer + MRT
in 720p. While it affects geometry processing with 1.2 - 1.3 times load, it
doesn't affect pixel processing as there's no overlapping unlike geometry.
As the result, it doesn't affect the total performance as pixel processing
load is inherently larger than that of geometry.
+ The hardware tesselator in Xenos supports both adaptive and sequential,
and adaptive tesselation requires 2-pass. If the tesselator is used the
vertex output from it is limited to 1 vertex per clock though the
performance impact can be mitigated as output vertices from the tesselator
have higher locality for better caching.
+ In a double-layer DVD for Xbox 360, 7GB is usable by a game. The transfer
rate of the DVD drive is 15MB/sec max, 10-12MB/sec average. The seek time is
115ms, switching layers takes 75ms. Loading 512MB data takes 34 seconds.
+ 2GB in the HDD is used for a temporary cache area for games. Its average
transfer rate is 17MB/sec and the average seek time is 13ms.
+ Game data is managed per user account and saved in HDD, but 64MB Memory
Unit is also usable for checkout/backup. The Memory Unit slot is 2.5MB/sec
write, 8MB/sec read.
+ In its 512MB RAM, 32MB is allocated for the system. The RAM is GDDR3 SDRAM
@ 700MHz (22.4GB/sec).
Diagrams:
http://pcweb.mycom.co.jp/articles/2005/09/09/cedec1/images/007l.jpg
http://pcweb.mycom.co.jp/articles/2005/09/09/cedec1/images/008l.jpg
http://pcweb.mycom.co.jp/articles/2005/09/09/cedec1/images/012l.jpg
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