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.