BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
222
Section 8: PCI Bus and HyperTransport Fabric
Document
1250_1125-UM100CB-R
PCI A
RBITER
The device incorporates a PCI bus arbiter that may be used when the interface is configured as the host bridge.
The arbiter supports four external devices in addition to the host. Arbitration is done using a single-ring round
robin scheme with the bus parked on the last granted device when there are no new requests. Except for the
hotplug situation described below, the arbiter will wait for up to 32 PCI clocks for the master to assert frame
before removing the grant (the "broken" master case of section 3.4.1 of the PCI specification), but requests
from the master will continue to be responded to and the arbiter does not have a status register that records
this being done.
The arbiter includes support for hotplug systems. When the hotplug_en bit is set in the Additional Status and
Control Register (at 88 in the PCI configuration registers) and P_REQ_L[3] is asserted, once
P_GNT_L[3] is granted it will be held in the asserted (granted) state as long as P_REQ_L[3] is asserted,
independent of higher priority requests. In addition to enabling hot plug systems, this can be used to solve
some arbitration problems in some older southbridge devices.
PCI I
NTERRUPTS
The PCI interface includes 4 active low interrupt lines P_INTA_L-P_INTD_L. When used as a host the interface
will normally use all of these as the interrupt inputs from the other PCI devices (the PCI specification describes
the recommended way of permuting these as they are connected to the INTA#-INTD# pins of slots or devices).
In all cases the four lines are monitored as active low interrupt inputs and the results presented to the interrupt
mapper as sources 56-59 (see
Table 22: “Interrupt Sources,” on page 52
). Any of the inputs that are not used
by PCI devices can therefore be used as general active low interrupt inputs.
The P_INTA_L signal can also be driven (as an open collector output) by the interface (note that when it is
driven low the input logic will detect that it is low and raise system interrupt 56). This is intended for use in
device mode to allow an interrupt to be driven to the host (see
Section: “Using the PCI in Device
). However, the output can still be driven when the interface is configured for host mode so
a system that does not need four PCI interrupt inputs may choose to use the P_INTB_L-P_INTD_L for PCI use
and use P_INTA_L as a general open collector I/O.
H
YPER
T
RANSPORT
D
IFFERENCES
FROM
R
EVISION
0.17 S
PECIFICATION
This section lists the main differences between the HyperTransport Specification Revision 0.17 and the
interface implemented in the BCM1250 and BCM1125H. Since there was only limited distribution of the 0.17
specification, most readers will find the next section (differences from revision 1.03) more useful.
1
The transmitters drive UNPREDICTABLE data on the CAD and CTL lines during CRC testing mode.
2
Non-zero byte masks for double words which are not sent are ignored.
3
Five additional error conditions are reported: Protocol error detected on the link; Receive FIFO overflow error;
Response received with a srctag that has no corresponding request; End-of-chain NXA error issued to the link;
and NXA error issued to a request from a peer host bridge (a request with a source tag of zero).
4
The interface has 4 responses to errors. Localized errors result in an error response. The remaining errors can
be set to result in sync flooding, raising the HyperTransport fatal error interrupt or raising the HyperTransport
non-fatal error interrupt.
5
If the isochronous bit is set in a HyperTransport request that is sent to the ZBbus, it will have the L2 cache
allocate bit set in the ZBbus command.
Содержание BCM1125
Страница 18: ...BCM1250 BCM1125 BCM1125H User Manual 10 21 02 Broadcom Corporation Page xviii Document 1250_1125 UM100CB R ...
Страница 28: ...BCM1250 BCM1125 BCM1125H User Manual 10 21 02 Broadcom Corporation Page xxviii Document 1250_1125 UM100CB R ...
Страница 515: ...BCM1250 BCM1125 BCM1125H User Manual 10 21 02 Broadcom Corporation Page vii Index Document 1250_1125 UM100CB R ...