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SKYchannel Interconnect: Increasing System Bandwidth
At the heart of the SKYbolt and Thunderbolt systems is the 64-bit ANSI/VITA
standard SKYchannel Packet Bus. SKYchannel is the on-board communication
path connecting the VME64 interface, the SKYrider parallel I/O, the System
Processor, the compute modules, and high speed communication between
Thunderbolt boards. The 320 MB/sec bandwidth coupled with SKY's
crossbar architecture provides for multiple, simultaneous
operations increasing available system bandwidth. SKYchannel provides
reduced connection latency, split transaction, full-speed transfers,
and forward progress mentioned above, the SKYchannel architecture
brings several critical benefits to the application developer.
Large Flat Memory Space
SKYchannel provides for a memory-mapped 16 Terabtye address space. This
enables application processors to perform simple loads and stores to
access remote resources. Each VME board is allocated a 64 GB address
space, which is more than sufficient to address all memory on a common
VME memory board.
Built-in Error Detection
Transmission of data on a VME board and even between boards on a
backplane is not error prone with current technology. However, for
mission-critical applications where the highest data integrity is
required, SKYchannel provides built-in error detection where there is
the highest probability of an error, namely in the network connections
between boards. This error detection is handled transparently by the
hardware, as described below, by appending a checkword to each packet
as it transits the backplane.
The decoupling FIFOs and the modular interface of SKYchannel enables various
types of processors to be interconnected. The speed of the processor's
external memory bus does not need to be matched directly to the speed of
320 MB/sec for each path
Having a fast, wide connection for each communication path is much better
than trying to combine multiple slower connections to achieve the same
aggregate performance. This is because each processor can use only one
connection at a time and a fast processor will back up on a slower connection.
Multiple SKYbolt or Thunderbolt boards can be connected for a total of
up to 1600 MB/sec of bandwidth.