Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | |
2 | Below is what the bt878 data book says about the PCI bug compatibility | |
3 | modes of the bt878 chip. | |
4 | ||
5 | The triton1 insmod option sets the EN_TBFX bit in the control register. | |
6 | The vsfx insmod option does the same for EN_VSFX bit. If you have | |
7 | stability problems you can try if one of these options makes your box | |
8 | work solid. | |
9 | ||
10 | drivers/pci/quirks.c knows about these issues, this way these bits are | |
11 | enabled automagically for known-buggy chipsets (look at the kernel | |
12 | messages, bttv tells you). | |
13 | ||
14 | HTH, | |
15 | ||
16 | Gerd | |
17 | ||
18 | ---------------------------- cut here -------------------------- | |
19 | ||
20 | Normal PCI Mode | |
21 | --------------- | |
22 | ||
23 | The PCI REQ signal is the logical-or of the incoming function requests. | |
24 | The inter-nal GNT[0:1] signals are gated asynchronously with GNT and | |
25 | demultiplexed by the audio request signal. Thus the arbiter defaults to | |
26 | the video function at power-up and parks there during no requests for | |
27 | bus access. This is desirable since the video will request the bus more | |
28 | often. However, the audio will have highest bus access priority. Thus | |
29 | the audio will have first access to the bus even when issuing a request | |
30 | after the video request but before the PCI external arbiter has granted | |
31 | access to the Bt879. Neither function can preempt the other once on the | |
32 | bus. The duration to empty the entire video PCI FIFO onto the PCI bus is | |
33 | very short compared to the bus access latency the audio PCI FIFO can | |
34 | tolerate. | |
35 | ||
36 | ||
37 | 430FX Compatibility Mode | |
38 | ------------------------ | |
39 | ||
40 | When using the 430FX PCI, the following rules will ensure | |
41 | compatibility: | |
42 | ||
43 | (1) Deassert REQ at the same time as asserting FRAME. | |
44 | (2) Do not reassert REQ to request another bus transaction until after | |
45 | finish-ing the previous transaction. | |
46 | ||
47 | Since the individual bus masters do not have direct control of REQ, a | |
48 | simple logical-or of video and audio requests would violate the rules. | |
49 | Thus, both the arbiter and the initiator contain 430FX compatibility | |
50 | mode logic. To enable 430FX mode, set the EN_TBFX bit as indicated in | |
51 | Device Control Register on page 104. | |
52 | ||
53 | When EN_TBFX is enabled, the arbiter ensures that the two compatibility | |
54 | rules are satisfied. Before GNT is asserted by the PCI arbiter, this | |
55 | internal arbiter may still logical-or the two requests. However, once | |
56 | the GNT is issued, this arbiter must lock in its decision and now route | |
57 | only the granted request to the REQ pin. The arbiter decision lock | |
58 | happens regardless of the state of FRAME because it does not know when | |
59 | FRAME will be asserted (typically - each initiator will assert FRAME on | |
60 | the cycle following GNT). When FRAME is asserted, it is the initiator s | |
61 | responsibility to remove its request at the same time. It is the | |
62 | arbiters responsibility to allow this request to flow through to REQ and | |
63 | not allow the other request to hold REQ asserted. The decision lock may | |
64 | be removed at the end of the transaction: for example, when the bus is | |
65 | idle (FRAME and IRDY). The arbiter decision may then continue | |
66 | asynchronously until GNT is again asserted. | |
67 | ||
68 | ||
69 | Interfacing with Non-PCI 2.1 Compliant Core Logic | |
70 | ------------------------------------------------- | |
71 | ||
72 | A small percentage of core logic devices may start a bus transaction | |
73 | during the same cycle that GNT is de-asserted. This is non PCI 2.1 | |
74 | compliant. To ensure compatibility when using PCs with these PCI | |
75 | controllers, the EN_VSFX bit must be enabled (refer to Device Control | |
76 | Register on page 104). When in this mode, the arbiter does not pass GNT | |
77 | to the internal functions unless REQ is asserted. This prevents a bus | |
78 | transaction from starting the same cycle as GNT is de-asserted. This | |
79 | also has the side effect of not being able to take advantage of bus | |
80 | parking, thus lowering arbitration performance. The Bt879 drivers must | |
81 | query for these non-compliant devices, and set the EN_VSFX bit only if | |
82 | required. | |
83 |