28500-DSH-002-C_15 Datasheet, PDF (79/224 Pages) M/A-COM Technology Solutions, Inc. – Multichannel Synchronous Communications Controller

Serial Interface
5.1.7
Polling
After channel activation, CX28500 must fetch Message Descriptors (MD) from shared memory to start the
message flow in and out of shared memory.
As an MD is fetched, CX28500 checks the owner bit to verify whether the buffer is available for CX28500. If the
owner bit indicates that the Host still owns the buffer, the Host has not prepared the data for processing in the data
buffers. If poll bit is enabled, CX28500 polls the Buffer Descriptor until the owner bit is switched to CX28500-owned.
If the owner bit is still Host-owned and no poll (NP = 1) and if TONRIEN/RONRIEN bit field is set to 1 in TDMA
Channel Configuration register or RDMA Channel Configuration register, an (ONR) interrupt is generated toward
the Host.
If the Host owns the buffer and polling is enabled, the channel direction is suspended from processing messages,
and CX28500 periodically polls the owner bit in the Buffer Descriptor until the owner bit is CX28500-owned. The
channel is capable of leaving this suspended state autonomously. Figures 5-1 and 5-2 illustrate the details.
Figure 5-1. RDMA State Machine
Always
INHRBSD = 1 While there is an EOM or EOB
Read
Message
Descriptor
(MD)
CX28500 - Owned
Owner = 0
Poll (NP = 0)
Host - Owned
(Owner = 1)
CX28500 Owns
the BD
Write
Data
Poll (NP = 0)
CX28500 Owned
(Owner = 0)
Poll
Buffer
Descriptor
(BD)
Not
EOM
Host - Owned
(Owner = 1)
NP = 1
Not
EOB
INHRBSD = 0
(Allow Status
Write)
EOM or
EOB
Write
Buffer Status
Descriptor
(BSD)
CH_ACT
Read
Head
Pointer
CH_JUMP
CH_ACT
RDMA
Suspend
State
ONR
ONRIEM = 1
RxONR
500052_054
28500-DSH-002-C
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