Protocol for Disconnecting from a System I/O Bus during a Graphics Load Instruction
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Arimilli, LB: AUTHOR [+2]
Disclosed is a method to disconnect from a RS/6000* System I/O (SIO) bus during a high performance graphics PIO load operation which has locked the bus.
Protocol for Disconnecting from a System I/O Bus during a
a method to disconnect from a RS/6000* System I/O
(SIO) bus during a high performance graphics PIO load operation which
has locked the bus.
The SIO Bus
supports two types of PIO loads, one for normal PIO
load performance, and one for high performance PIO loads for
graphics. The normal PIO load protocol requires that the I/O
controller (which provides the interface between the SIO Bus and the
graphics adapters), after receiving the PIO load request on the SIO
bus, must generate a request for the SIO bus when the load reply data
is ready, and be granted the SIO bus by the Storage Control Unit
(SCU) before sending the load reply data on the SIO bus. The high
performance PIO load protocol does not require the I/O controller to
arbitrate for the SIO bus as the SIO bus is granted to the I/O
controller for the duration of the PIO load transfer. During these
operations no other device is granted access to the bus.
scenarios during a high performance PIO load
operation that require the I/O controller to release the SIO bus and
when ready re-arbitrate for the SIO bus to send the load reply data
(effectively converting a high performance PIO load to a normal PIO
load). For example, one of these scenarios occurs when a graphics
adapter is too slow in sending the load reply packet back to the I/O
controller. The SIO bus is unnecessarily blo...