User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 8: PCI Bus and HyperTransport Fabric Page
259
Buffer Control: TxBufCountMax and DataBufAlloc
The Transmit Buffer Count Max register sets the maximum number of buffers the transmitter will use in each
of the six buffer classes described in the HyperTransport Specification. The classes (Posted Command,
Posted Data, NonPosted Command, NonPosted Data, Response and Response Data) match the buffers in
the receiver and fields in the NOP flow control packet.
NOP packets received from the other end of the link will increment the number of buffers that the transmitter
believes the receiver has available. If the count reaches the limit set in this register the extra credits will be
discarded. This allows a general way to throttle traffic in a particular virtual channel on a link.
The
DataBufAlloc
register allows allocation of the HyperTransport receive data buffers between the three
virtual channels. The minimum number of buffers that must remain allocated to each channel is specified,
along with the number of additional buffers that the dynamic buffer allocator should try to make available for
that channel.
H
YPER
T
RANSPORT
R
ESETS
There are four reset conditions associated with the HyperTransport. This section describes them and their
actions on the HyperTransport link and interface. The four resets are:
1
System cold reset. A system cold reset is caused by the assertion of COLDRES_L or the setting of the system
configuration register system_reset bit. This reset causes the subsequent assertion of all other resets detailed
here.
2
System warm reset. A system warm reset is caused by the assertion of RESET_L or the setting the system
configuration register sb_softres bit and results in the assertion of link reset.
3
HyperTransport link power ok (LDT_PWROK). This open drain output is driven and received by the interface.
The HyperTransport link is inactive if this signal is not asserted.
4
HyperTransport link reset (LDT_RESET_L). This open drain output is driven and received by the interface. The
HyperTransport link is reset when this signal is asserted, a cold link reset will be performed if LDT_PWROK is
deasserted and a warm link reset if LDT_PWROK is asserted.
Following a system cold reset the interface will drive the HyperTransport link controls to ensure LDT_PWROK
will remain deasserted and LDT_RESET_L will remain asserted until the SipReady bit has been set in the
HyperTransport SRI Command register. Once the bit is set LDT_PWROK will be asserted and 1ms later
LDT_RESET_L will be deasserted to start the cold link initialization. These are inputs as well as open drain
outputs, so other devices in the chain can hold off starting the link (for example in a double hosted link the parts
at each end of the link may take different lengths of time to complete their initialization and set SipReady). Note
that writing the SRI configuration registers and setting of the SipReady bit should only be done after a system
cold reset, the SipReady bit must not be touched during link resets.
As required by the HyperTransport specification, a deassertion of LDT_PWROK is caused by clearing the
warm reset bit in the HyperTransport Command Register and setting the SecBusReset bit in the
HyperTransport Bridge Control Register. This is effectively a cold reset on the HyperTransport link and also
causes the assertion of the link reset.
As required by the HyperTransport specification, an assertion of link reset is caused by setting the warm reset
bit in the HyperTransport Command Register and setting the SecBusReset bit in the HyperTransport Bridge
Control Register. This is effectively a HyperTransport link warm reset.
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 ...