S2020/S2021 SOURCE DEVICE STATE MACHINES
CONNECT SM EXTERNAL INPUTS
MSEL2-0
Mode SELect lines 2-0 from the Source
Host. Although there are eight possible modes for
the Source device selected by these signals, only
modes 0 (RESET), 2 (WAIT), and 3 (OPERA-
TIONAL) are part of this discussion.
CNREQ
CoNnect REQuest signal from the Source
Host. A ‘1’ on this signal indicates the Source
Host’s request to either initiate a connection or
maintain the current connection on the HIPPI chan-
nel.
A ‘0’ on this signal indicates the Source Host’s re-
quest to either terminate the current connection or
maintain a disconnected state on the HIPPI chan-
nel.
DSIC
Destination to Source InterConnect signal from
the HIPPI channel. A ‘0’ on this signal indicates the
presence of a functioning Destination on the HIPPI
channel. A ‘1’ on this signal indicates the absence
of a functioning Destination on the HIPPI channel.
CON
CONnect signal from the HIPPI channel. The
functions of this signal are defined in the HIPPI-PH
spec.
RDY
ReaDY signal from the HIPPI channel. The func-
tions of this signal are defined in the HIPPI-PH
spec.
NOTE: The input signals from the HIPPI channel go
through a digital ‘filter’ in the Source device. This filter
circuit resolves metastability (of the asynchronous sig-
nals) and filters out any signal state changes which are
less than two cycles in duration.
HIPPI
{IDLE}
The IDLE state: This is the first operational state
entered from {INIT} (above). The main entrance to
this state is when this circuit is in the {INIT} state
and the inputs specify “I”. While in this state, both
Source and Destination are ready and waiting for a
connection to be established.
{REQ}
The REQuest state is entered from the {IDLE}
state when the Source Host initiates a HIPPI con-
nection by asserting CNREQ. This state is exited
when the Source Host drops CNREQ (abort) or
when CON goes active, indicating a Destination re-
sponse to the connect request.
{CON1}
The CONnect1 state is entered from the
{REQ} state for one cycle when CON first goes
active, indicating a Destination response to the con-
nect request. From this state, the request may be
aborted, or the response will continue to be pro-
cessed.
{CONn, 1<n<16}
These 14 states differentiate be-
tween a CONNECT ACCEPT and a CONNECT
REJECT response from the Destination. Being in
one of these states implies that CON has been
active (from the Destination) for 2 to 15 consecutive
cycles. Receiving “CR” (inactive CON) in one of
these states is a CONNECT REJECT. Receiving a
“RDY” in one of these states indicates a CONNECT
ACCEPT. Receiving “DR” in one of these states
indicates that the Source Host wishes to abort the
request.
{CON16}
CONnect 16 state is entered for one cycle
when the sixteenth consecutive cycle of an active
CON from the Destination is received. Receiving
“C” or “RDY” in this state constitutes a CONNECT
ACCEPT. Receiving a “CR” in this state indicates a
CONNECT REJECT response from the Destina-
tion. NOTE: The ‘filter’ circuit that the CON signal
goes through effectively truncates the end of an
active CONNECT signal, thereby allowing this state
machine to wait 16 cycles (rather than 17) to deter-
mine if the Destination response is ACCEPT or RE-
JECT. Receiving “DR” in this state indicates that
the Source Host wishes to abort the connect
requets operation.
{CONNECTED}
CONNECTED state is entered when a
valid connection is established across the HIPPI
channel between the Source and Destination. Re-
ceiving a “CR” in this state indicates an illegal termi-
nation, initiated by the Destination. Receiving a
“DR” in this state results in a connection termina-
tion, initiated by the Source Host.
CONNECT SM INTERNAL STATES
The defined states and brief descriptions of each state
follow.
{INIT}
The INITialization state is the state from which
the rest of the functional connect states are en-
tered. The main entrance to this state is when the
inputs specify “RST”, i.e., modes 0 or 2 with DSIC =
0 (active). The “RST” input indicates that the HIPPI
Destination is present and that the Source Host is
holding this device in a RESET or WAIT mode. It is
intended that the Source Host enter the OPERA-
TIONAL mode (3) when DSIC becomes active and
when the Source Host is ready to enter the opera-
tional* states of this CONNECT SM (for HIPPI con-
nections).
* The operational states of this CONNECT SM are all but {INIT}, {LOSTDEST}, and {NODEST}.
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