SBPH400-3 查看數據表（PDF） - STMicroelectronics
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SBPH400-3 Datasheet PDF : 43 Pages
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SBPH400-3
The Request Type field is encoded as specified in Table 2.10:
Table 2.12 Request type field
LR[1:3] Name
Description
000
ImmReq
Used for Acknowledge Transfers. The SBPH400 takes control of the bus
immediately upon detecting idle without arbitration.
001
IsoReq
Used for Isochronous Transfers. The SBPH400 arbitrates after an
isochronous gap, or transmits immediately if an isochronous packet has
just been received from a child port (fly-by arbitration). The SBPH also
performs accelerated arbitrations (see AccCtrl below) after receiving this
request if the enab_accel register is set to 1.
010
PriReq
Used for Cycle Master requests. The SBPH400 arbitrates after a
subaction gap or, if acceleration enhancements are enabled (enab_accel
register is set to 1) and if accelerate control has been set to allow
accelerations (see AccCtrl below), arbitrates after an ACK packet has
been received, or transmits immediately if an ACK packet has just been
received on a child port (see Accelerate/Decelerate below), ignoring the
fair protocol. This is also used for the second and subsequent optimized
fair transfers
011
FairReq
Used for Fair Transfers. Used for Fair Transfers. The SBPH400 normally
arbitrates after subaction gap. If acceleration enhancements are enabled
(enab_accel register is set to 1) and if accelerate control has been set to
allow accelerations (see AccCtrl below), then the SBPH400 will arbitrate
after an ACK packet has been received, or transmit the packet
immediately if an ACK packet has been received on a child port. In all
cases the SBPH400 follows the fair protocol (one FairReq packet per
arbitration reset gap).
100
RdReg
Return specified register contents through a status transfer.
Note that the result is undefined if a previous RdReg request has not been
completed.
101
WrReg
Write to specified register.
110
AccCtrl
Accelerate control. The link should send an AccCtrl request with
Acceleration_Select = 0 (Decelerate) if it is not root and when its cycle
timer has counted a 125 µs interval. The SBPH400 will not employ ACK
accelerated arbitration or fly-by arbitration for asynchronous packets until
a subsequent Accelerate request with Acceleration_Select = 1
(Accelerate) is received or an IsoReq has been received. The link should
send an Accelerate request with Acceleration_Select = 1 after it has
received a cycle start packet if it has no isochronous packets to transmit
in the current isochronous cycle.
111
reserved
ignored
19/43
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