Stall Detection - STMicroelectronics SPC572L series Reference Manual

Nexus Aurora Router (NAR)
supported in the PD NAR, it is not supported in the BD NAR. A suppress can either be
global, meaning messaging is turned off for all clients, or local, which only applies to
selected clients. In suppress mode, the NAR pulls messages from the suppressed client(s),
but does not queue or deliver them. After extracting the MSEO bits to keep track of
message boundaries, the rest of the message is discarded. This allows the NAR to better
keep up with fast-running Nexus clients without having to turn off messaging in the client.
Typically, a client would be suppressed during less interesting periods, and would be
awakened when some preset condition is detected. This is communicated to the NAR via
the one of the suppress triggers, which can be sourced by a client or an external Event
Processing block. When an enter suppress trigger is received, the NAR output queue
finishes servicing the current active ports until the end of the message. If the end of the
message occurs in a middle beat of a Nexus word, then the remainder of the word is
padded with null messages. Once the last message has been loaded into the output queue,
the receive queues are all emptied. New messages are pulled from clients as they appear,
go through their respective receive queues and then are discarded. In this way, the NAR
can naturally monitor the MSEO bits and keep track of each client's Nexus state. In
suppress mode, the output ports remain active until the output queue is emptied, meaning
there is a delay between the assertion of the suppress trigger and the end of messaging.
When the NAR is in suppress mode and receives a wake-up trigger, it continues discarding
any partial messages still in the receive queues. Any message that begins after the trigger is
queued normally, insuring that only complete messages are sent to the output queue.
Global suppress mode applies to all clients. Any of the suppress triggers can be
programmed to cause the NAR to toggle between suppressed and awake by setting the
GST bit of the associated Suppress Trigger Control Register (NAR_STCR). Additionally, the
NAR starts up in global suppress mode if the PUS bit of the Control Register is set when the
NAR is enabled. All clients are then suppressed until a wake-up trigger is received. If the
PUS bit is set without enabling any of the triggers for global suppress, a configuration error
results and the NAR powers up in active mode.
Clients can go also into local suppress mode without putting the entire NAR to sleep. Each
NAR_STCR has a 16-bit LST field. Setting one or more of these bits causes the trigger
assigned to that NAR_STCR to toggle the associated clients between suppressed and
awake. All other clients are unaffected. Thus, suppress trigger one can be assigned to one
set of clients, while suppress trigger two can be assigned to another set of clients, and
different parts of the device can be ignored at different times, all based on different,
programmable events. Global suppress always has higher priority than local suppress. That
is, if the NAR is in global-suppressed mode, any local suppress wake-up triggers are
ignored. Also, if some clients are in local suppress when a global suppress trigger hits, then
all go into suppress mode; however, upon the subsequent global wake-up, the clients that
were previously in local suppress remain so.
65.5.5

Stall detection

Since the NAR can only switch between clients on an end-of-message boundary, every
message that goes into the NAR must complete. If a client happens to die or stall in the
middle of transmitting a message, this uncompleted message could cause the NAR to stall,
at a time when other clients might still be able to deliver useful information. To prevent this
from occurring, the NAR monitors each client for a stall condition, which is defined as
occurring when data is not valid in the middle of a Nexus message for a set number of
cycles.
1892/2058 DocID027809 Rev 4
RM0400