83 lines
3.7 KiB
Text
83 lines
3.7 KiB
Text
|
|
Below is what the bt878 data book says about the PCI bug compatibility
|
|
modes of the bt878 chip.
|
|
|
|
The triton1 insmod option sets the EN_TBFX bit in the control register.
|
|
The vsfx insmod option does the same for EN_VSFX bit. If you have
|
|
stability problems you can try if one of these options makes your box
|
|
work solid.
|
|
|
|
drivers/pci/quirks.c knows about these issues, this way these bits are
|
|
enabled automagically for known-buggy chipsets (look at the kernel
|
|
messages, bttv tells you).
|
|
|
|
HTH,
|
|
|
|
Gerd
|
|
|
|
---------------------------- cut here --------------------------
|
|
|
|
Normal PCI Mode
|
|
---------------
|
|
|
|
The PCI REQ signal is the logical-or of the incoming function requests.
|
|
The inter-nal GNT[0:1] signals are gated asynchronously with GNT and
|
|
demultiplexed by the audio request signal. Thus the arbiter defaults to
|
|
the video function at power-up and parks there during no requests for
|
|
bus access. This is desirable since the video will request the bus more
|
|
often. However, the audio will have highest bus access priority. Thus
|
|
the audio will have first access to the bus even when issuing a request
|
|
after the video request but before the PCI external arbiter has granted
|
|
access to the Bt879. Neither function can preempt the other once on the
|
|
bus. The duration to empty the entire video PCI FIFO onto the PCI bus is
|
|
very short compared to the bus access latency the audio PCI FIFO can
|
|
tolerate.
|
|
|
|
|
|
430FX Compatibility Mode
|
|
------------------------
|
|
|
|
When using the 430FX PCI, the following rules will ensure
|
|
compatibility:
|
|
|
|
(1) Deassert REQ at the same time as asserting FRAME.
|
|
(2) Do not reassert REQ to request another bus transaction until after
|
|
finish-ing the previous transaction.
|
|
|
|
Since the individual bus masters do not have direct control of REQ, a
|
|
simple logical-or of video and audio requests would violate the rules.
|
|
Thus, both the arbiter and the initiator contain 430FX compatibility
|
|
mode logic. To enable 430FX mode, set the EN_TBFX bit as indicated in
|
|
Device Control Register on page 104.
|
|
|
|
When EN_TBFX is enabled, the arbiter ensures that the two compatibility
|
|
rules are satisfied. Before GNT is asserted by the PCI arbiter, this
|
|
internal arbiter may still logical-or the two requests. However, once
|
|
the GNT is issued, this arbiter must lock in its decision and now route
|
|
only the granted request to the REQ pin. The arbiter decision lock
|
|
happens regardless of the state of FRAME because it does not know when
|
|
FRAME will be asserted (typically - each initiator will assert FRAME on
|
|
the cycle following GNT). When FRAME is asserted, it is the initiator s
|
|
responsibility to remove its request at the same time. It is the
|
|
arbiters responsibility to allow this request to flow through to REQ and
|
|
not allow the other request to hold REQ asserted. The decision lock may
|
|
be removed at the end of the transaction: for example, when the bus is
|
|
idle (FRAME and IRDY). The arbiter decision may then continue
|
|
asynchronously until GNT is again asserted.
|
|
|
|
|
|
Interfacing with Non-PCI 2.1 Compliant Core Logic
|
|
-------------------------------------------------
|
|
|
|
A small percentage of core logic devices may start a bus transaction
|
|
during the same cycle that GNT is de-asserted. This is non PCI 2.1
|
|
compliant. To ensure compatibility when using PCs with these PCI
|
|
controllers, the EN_VSFX bit must be enabled (refer to Device Control
|
|
Register on page 104). When in this mode, the arbiter does not pass GNT
|
|
to the internal functions unless REQ is asserted. This prevents a bus
|
|
transaction from starting the same cycle as GNT is de-asserted. This
|
|
also has the side effect of not being able to take advantage of bus
|
|
parking, thus lowering arbitration performance. The Bt879 drivers must
|
|
query for these non-compliant devices, and set the EN_VSFX bit only if
|
|
required.
|
|
|