XIO - Revision history

Onion at 07:00, 8 October 2010

2010-10-08T07:00:55Z

Skylark at 20:32, 13 February 2005

2005-02-13T20:32:21Z

Ralf: /* Link layer */

2004-11-05T08:40:28Z

‎Link layer

150.254.31.62 at 08:19, 5 November 2004

2004-11-05T08:19:17Z

150.254.31.62 at 08:18, 5 November 2004

2004-11-05T08:18:24Z

New page

== What is XIO? ==

XIO is a high-speed communications channel, used for most newer SGI systems ([[IP27]], [[IP30]], [[IP35]] - note the [[IP32|O2]] is NOT a XIO system). It's typically used in a switched star topology, the switch being called [[XBow]].

XIO devices are called [[widget|widgets]]].

== Physical layer ==

XIO is usually used on a single-ended, source-synchronous physical layer (STL levels - SGI Transistor Logic). It's either an 8- or 16-bit channel, running at 400 MHz (using the dreaded compression connectors). There is also a version, called Crosstown, that uses normal cabling and differential PECL transmission.

== Link layer ==

XIO contains a link-layer protocol (LLP) shared with [[CrayLink]]. Transfer is organized into micropackets. These contain a total of 128 bits of data and 32 bits of control. The control information encapsulates an 8 bit sideband (used by higher layers for framing), sequence numbers (for go-back-n link-layer retransmissions) and check bits (CRC-16).

The link layer is able to run both on 8- and 16-bit links, and if a upper half of a 16-bit link is non-functional, it will automatically revert to using the 8 lower bits.

== Transactions ==

XIO supports basic read/write memory transactions. IRQs are sent through XIO by instructing a device to write a defined value to some register in another XIO widget. This write actually triggers the IRQ handling process in the interrupt controller. For instance, the [[HEART]] chip has such register at 0x80 in XIO widget space.

XIO addresses differ from physical processor addresses. They are two-part (widget-offset) and each XIO device is free to implement the translation from its unified memory space to the XIO address. [[BRIDGE]] and [[HEART]] are examples of two different approaches.

== Device identification ==

There is no distinction between memory and configuration space in XIO. Instead, each XIO device has a predefined header that consists of a [[widget|widget ID]] and several configuration registers.

← Older revision		Revision as of 07:00, 8 October 2010
Line 28:		Line 28:

	There is no distinction between memory and configuration space in XIO. Instead, each XIO device has a predefined header that consists of a [[widget\|widget ID]] and several configuration registers.		There is no distinction between memory and configuration space in XIO. Instead, each XIO device has a predefined header that consists of a [[widget\|widget ID]] and several configuration registers.
		+
		+	[[Category:SGI]]

← Older revision		Revision as of 20:32, 13 February 2005
Line 4:		Line 4:

	XIO devices are called [[widget\|widgets]].		XIO devices are called [[widget\|widgets]].
		+
		+	== Linux support ==
		+
		+	There is no explicit support for XIO in Linux/MIPS. (Of course there are supported devices using XIO, but there is no XIO layer yet.) A proposal for a XIO layer is here: [[XIO API]].

	== Physical layer ==		== Physical layer ==

@@ Line 11: / Line 11: @@
 == Link layer ==
-XIO contains a link-layer protocol (LLP) shared with [[CrayLink]]. Transfer is organized into micropackets. These contain a total of 128 bits of data and 32 bits of control. The control information encapsulates an 8 bit sideband (used by higher layers for framing), sequence numbers (for go-back-n link-layer retransmissions) and check bits (CRC-16).
+XIO contains a link-layer protocol (LLP) shared with [[CrayLink]]. Transfer is organized into micropackets. These contain a total of 128 bits of data and 32 bits of control. The control information encapsulates an 8 bit sideband (used by higher layers for framing), sequence numbers (for go-back-n link-layer retransmissions) and check bits ([http://en.wikipedia.org/wiki/Cyclic_redundancy_check CRC-16]).
 The link layer is able to run both on 8- and 16-bit links, and if a upper half of a 16-bit link is non-functional, it will automatically revert to using the 8 lower bits.

@@ Line 3: / Line 3: @@
 XIO is a high-speed communications channel, used for most newer SGI systems ([[IP27]], [[IP30]], [[IP35]] - note the [[IP32|O2]] is NOT a XIO system). It's typically used in a switched star topology, the switch being called [[XBow]].
-XIO devices are called [[widget|widgets]]].
+XIO devices are called [[widget|widgets]].
 == Physical layer ==