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Request Block
The system request portion of the List Processor is the top level coordinator of all activity. It
arbitrates the master requests, multiplexes the data and control signals to the Host Controller Bus
Master.
1) Master Arbitration
There are three sources of master requests from the List Processor: HCCA Writeback request
(HCCAWBReq), ED request (EDReq), and TD request (TDReq).
The HCCA Writeback has the highest priority. It is granted access to the Bus Master when its
request is acknowledged (HCCAWBAck). The request is acknowledged when neither the ED
or TD has access to the Bus Master (EDAck or TDAck) and the Bus Master is idle
(!bm_active).
The TD request and ED request are at the lowest priority. The state machine interaction will
prevent both requests from being active simultaneously. The individual request (TDReq or
EDReq) is granted access to the Bus Master when it is acknowledged (TDAck or EDAck). The
request is acknowledged when the HCCA Writeback request is not active and the Bus Master is
idle (!bm_active).
2) Data and Control Muxing
Master
The Request Block multiplexes the control and data signals to the Bus Master for the
submaster that has the acknowledge.
There are five control signals provided:
Table 18.12 List Processor Control Signals
Signal
Description
lp_SystemReq
List Processor system request. Asserted for one clock when the
submaster is granted its acknowledge.
lp_SystemReqIsData
Transfer is data.
lp_SystemReqIsRead
Transfer is read.
lp_ReqSize
Transfer size in bytes.
lp_BeginAddr
Transfer begin address.
The data from the submaster that has the acknowledge is multplexed onto the WriteDataOut
bus.
Slave
The Request Block multiplexes the slave read data from all of the operational registers in
the List Proccessor onto the ReadDataOut bus that goes to the IO module. The mux select
comes from the decode signals provided by the IO module.
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