SBPH400-3 datasheet(19/43 Pages) STMICROELECTRONICS

19 / 43 page

SBPH400-3

19/43

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

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

SBPH400-3 датащи(PDF) 19 Page - STMicroelectronics

SBPH400-3 датащи(HTML) 19 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

датащи скачать

ссылки URL