Request in Logic
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Beardsley, BC: AUTHOR [+2]
To support 32 logical channels per path it was necessary to improve the performance of the "Request In" function on the 3990. The "Request In" function was moved to hardware to support the improved performance and to free up the microcode interaction to support this function. The following elements make up the hardware management of the "Request In" function.
Request in Logic
To support 32
logical channels per path it was necessary to
improve the performance of the "Request In" function on the 3990.
The "Request In" function was moved to hardware to support the
improved performance and to free up the microcode interaction to
support this function. The following elements make up the hardware
management of the "Request In" function.
1. Request In Registers
2. Degate functions performed on these Request In registers
3. Logical Path Table
4. Inhibit Vectors
5. Rotational Priority Logic
See Fig. 1
for the layout of the Request In logic.
storage path updates the Request In register the hardware will start
processing that Request In. It first looks to see whether any degate
function is activated. If not it will further compute whether it is
a dynamic or status Request In. After resolving that it will
arbitrate among all the Request Ins to ensure the one with the
highest priority is selected. After determining the logical path the
hardware will read out the corresponding out serial address.
Registers - The Request In registers consist of four
types of registers indicating different types of "Request In"
information. An additional Dynamic Request In register was added to
provide a distinction from the storage path's perspective of a high
(dynamic) priority versus a low (static) priority "Request In".
1. Static Unsuppressible
2. CUE Owed
3. Static Suppressible
4. Dynamic Unsuppressible
Functions - The "Request In" function is degated by
certain conditions associated with the storage path. There are two
levels of degation: one degates all of the "Request Ins"; another
will degate only an individual channel's "Request In". Some of the
conditions that will cause a degate of all the "Request In" are the
1. Storage Path Processor stopped
2. Storage Path Locked and Selected
3. Storage Path Fenced
4. Storage Path Locked and Long Select Active
path also has a register which can individually
degate a logical channel.
Table - There is a logical path table that
contains one entry per logical channel. It is updated whenever a
logical path is established or removed. Each entry consists of:
o The 16 bit serial link address for that logical path.
o A 4 bit vecter
indicating whether the logical path is valid
(established) and if established for which associated physical
o A bit indicating whether the channel is a RECAP channel or not.
Vectors - There is an ESCON architecture requirement
that a request connection to a logical path cannot be retransmitted
for at least 50 microseconds after the request has been refused. The
hardware will manage a 32 bit inhibit vector which will keep track of
each individual channel to prevent the hardware from requesting a
reconnection to the same logical path mo...