Nexus3/ Module
e200z3 Power Architecture Core Reference Manual, Rev. 2
10-52
Freescale Semiconductor
10.12 Rules for Output Messages
e200z3-based class 3–compliant embedded processors must provide messages through the auxiliary port
in a consistent manner as described below:
•
A variable-length packet within a message must end on a port boundary.
•
A variable-length packet may start within a port boundary only when following a fixed-length
packet. If two variable-length packets end and start on the same clock, it is impossible to know
which bit is from the last packet and which bit is from the next packet.
•
Whenever a variable-length packet is sized such that it does not end on a port boundary, it is
necessary to extend and zero-fill the remaining bits after the highest order bit so that it can end on
a port boundary.
For example, if the nex_mdo[n:0] port is 2 bits wide and the unique portion of an indirect address TCODE
is 5 bits, the remaining 1 bit of nex_mdo[n:0] must be packed with a zero.
10.13 Auxiliary Port Arbitration
In a multiple Nexus environment, the Nexus3/ module must arbitrate for the shared Nexus port
at the SoC level.The request scheme is implemented as a 2-bit request with various levels of priority. The
priority levels are defined in
below. The Nexus3/ module receives a 1-bit grant signal
(npc_aux_grant) from the SoC level arbiter. When a grant is received, the Nexus3/ module begins
transmitting its message following the protocol outlined in
Section 10.11.2, “Pin Protocol.”
The
Nexus3/ module maintains control of the port, by asserting the nex_aux_busy signal, until the
MSEO state machine reaches the end message state.
10.14 Examples
The following are examples of program trace and data trace messages.
shows an example of an indirect branch message with 2 MDO/1 MSEO configuration.
shows the same example with an 8 MDO/2 MSEO configuration.
NOTE
During clock 12, the nex_mdo[n:0] pins are ignored in the single MSEO
case.
Table 10-34. MDO Request Encodings
Request Level
MDO Request Encoding
(nex_aux_req[1:0])
Condition of Queue
No request
00
No message to send
Low priority
01
Message queue less than half full
—
10
Reserved
High priority
11
Message queue at least half full
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