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參數(shù)資料
| 型號： | VRC4372-1 |
| 英文描述： | I/O CONTROLLER |
| 中文描述： | I / O控制器 |
| 文件頁數(shù)： | 13/66頁 |
| 文件大?。?/td> | 721K |
| 代理商： | VRC4372-1 |
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13
V
RC
4372 I/O Controller
5.1
PCI Arbitration
The V
RC
4372 I/O controller features an internal PCI arbiter that can be configured by
pulling the ARB pin high to arbitrate among six requestors (five external and one
internal), as specified by the bits programmed in the PAPC register. A reset selects a
rotating fair scheme. If the ARB pin is tied low, the V
RC
4372 does not perform
arbitration for the PCI bus and uses a logic 0 request grant pair to request the PCI bus
for internal requirements.
5.1.1
Rotating Fair
In this scheme, the priority of each requestor changes after every request, in round-
robin fashion, to give every request a fair chance to get on the bus. The rotation
sequence is as follows:
1.
2.
3.
Internal request
Requestors 0, 1, 2, 3, 4, 5
Internal request
If any of the requestors is not on, then the next requestor in the sequence becomes
the highest priority. After a requestor is granted the bus, it remains granted, depending
upon the setting of the TKYGNT bit.
5.1.2
Rotating Alternate 0
In this scheme, REQ0, if asserted, is granted the bus after every other transaction, as
follows:
0, 1, 0, 2, 0, 3, 0, 4, 0, 5, 0, i (internal), and then repeat
After a requestor is granted the bus, it remains granted, depending upon the setting of
the TKYGNT bit.
5.1.3
Rotating Alternate I
This scheme is identical to rotating alternate 0, except that the internal request is
given the advantage, as follows:
i, 0, i, 1, i, 2, i, 3, i, 4, i, 5, and then repeat
After a requestor is granted the bus, it remains granted, depending on the setting of
the TKYGNT bit.
5.2
PCI-to-I/O Bus
Arbitration Control
When a PCI-to-I/O bus request cannot be granted immediately by the I/O bus arbiter,
the V
RC
4372 I/O controller can wait up to four clock cycles before generating a PCI
bus retry. Refer to Section 6.5.3 for additional information.
5.3
PCI Interface Timer
(DSCTIM, RTYTIM)
5.3.1
Disconnect Timer (DSCTIM)
The DDCTIM times out a burst operation when the bridge is a target. Because the
V
RC
4372 cannot take a burst operation as a target, this timer is not necessary.
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