First about display-cfg. It describes what type of screen is attached.
The last two bytes are made up as following:
If some condition (unknown yet, we thought it had to do with if a screen is attached to that output, which it had not) is met we get:
BYTE: Display-Number BYTE: I2C Read Offset BYTE: 0xFF BYTE: 0xFF
If the unknown condition above is not met its build up as following regarding the type of screen attached.
BYTE: Display-Number BYTE: I2C Read Offset BYTE: 0xFF BYTE: 0x00
BYTE: Display-Number BYTE: I2C Read Offset BYTE: 0xFF BYTE: 0x01
And for everything else like LVDS, TMDS and Display-Port
BYTE: Display-Number BYTE: I2C Read Offset BYTE: DCB Entry OR (guessing) BYTE: 0x03
There is one display-cfg for each screen. Here an example (note we have to swap bytes to inject):
@0,display-cfg <00FFXX00> XX = I2C Read Offset @1,display-cfg <00FFXX01> XX = I2C Read OffsetTV
@0,display-cfg <01FFXX00> XX = I2C Read Offset @1,display-cfg <01FFXX01> XX = I2C Read OffsetELSE
@0,display-cfg <03YYXX00> XX = I2C Read Offset; YY = DCB ENTRY OR VALUE (guessing) @1,display-cfg <03YYXX01> XX = I2C Read Offset; YY = DCB ENTRY OR VALUE (guessing)
Now about NVCAP: It describes which outputs can be used simultaneously and the following:
BYTE: NVCAP_VERSION (hardcoded, goes from 0 to 5) BYTE: HAS_CLAM_SHELL (lid) BYTE: UNKNOWN (most built-in cards and MacPro 7300GT have that set to 1) BYTE: UNKNOWN (most built-in cards have that set to 1. something about backlight?) WORD: OUTPUT GROUP 3 (guessing, it describes what outputs are usable together with S-Video out) WORD: OUTPUT GROUP 1 (describes what outputs are grouped to Display-A) WORD: OUTPUT GROUP 2 (describes what outputs are grouped to Display-B) BYTE: BYTE: BYTE: BYTE: BYTE: BUILT-IN (guessing, built-in cards apart from 7300GO (AppleTV) have this set to 1) BYTE: UNKNOWN (hardcoded value) BYTE: EDID_MANUFACTURER_RESERVED_TIMINGS (BYTE 0x25 of the primary screens EDID) BYTE: BYTE: BYTE: UNKNOWN (MacBookPro 8600MGT (15") 128MB Vram has this set to 1)
About the Output groups, they are generated like following. It all depends on the DCB table in your video bios. You can find your DCB table by looking at offset 0x36 of a nvidia bios. You byte swap the word at 0x36, thats the address of the DCB table.
In the DCB table we have entries describing what type of connection can be used for a physical output, like ANALOG, ANALOG/DVI etc. Let's take an example DCB (iMac 7600GT).
DCB ENTRY 0: ANALOG DCB ENTRY 1: LVDS DCB ENTRY 2: TMDS DCB ENTRY 3: TV
In this case we have LVDS at index 1 (so we set bit 1), it is always alone on an output group. So OUTPUT GROUP 1 would be
hex: 0x0002 binary: 0000 0000 0000 0010
All the other entries will be grouped to OUTPUT GROUP 2, so we have DCB ENTRY 0,2 and 3 (so we set bit 0,2 and 3) grouped which would be
0x000D binary 0000 0000 0000 1101
As you can see we set bit X (X is the DCB ENTRY INDEX) to group an entry to an output group.
The same is done for OUTPUT GROUP 3, it's just generated when we have a TV entry in our DCB. It would be of big help if somebody with iMac 7600GT an tell us what outputs do work simultaneously with an S-Video adapter since iMac 7600GT is the only one having just the TV entry in this output group.
Now about NVMT: it describes the capabilities of the primary screen:
BYTE: NVMT_VERSION BYTE: DISPLAY_TYPE (0 = ANALOG, 1 = TV, 3 = the rest) BYTE: UNKNOWN BYTE: UNKNOWN WORD: EDID_MANUFACTURER WORD: EDID_PRODUCT_CODE WORD: SCREEN WIDTH WORD: SCREEN HEIGHT WORD: SCREEN WIDTH + SOME VALUE WORD: SCREEN WIDTH + SOME VALUE WORD: SCREEN WIDTH + SOME VALUE WORD: ZEROED WORD: SCREEN HEIGHT + SOME VALUE WORD: SCREEN HEIGHT + SOME VALUE WORD: SCREEN HEIGHT + SOME VALUE WORD: ZEROED DWORD: SOME VALUE * 10000 WORD: BYTE: BYTE: --BYTE: BYTE: BYTE: 7 DWORDS: ZEROED BYTE: 0xFF HARDCODED BYTE: 0xFF HARDCODED 6 BYTES: ZEROED DWORD: BYTE: BYTE: 6 BYTES: ZEROED BYTE: BYTE: BYTE: BYTE: --WORD: the --BYTE is this value >> 8 BYTE: BYTE:
Looking at NVMT is quite a mess, too much is unknown yet. If somebody has any further info for instance how to calculate the screen width/height values please help.
according to 8800GT Efi driver it is:
SUBSYSTEM_ID << 16 | 0x02FFbuilt-in
injected when the card is built-in. To check with: REGISTER STRAP_INFO_2 & 0x10device-type
injected when there is a second screen available at boot.@X,built-in, @X,use-backlight-blanking
injected when the attached screen is fixed and not removable (LVDS)@0,AAPL,boot-display
injected for the primary screen@X,backlight-control
injected with the value of AAPL,backlight-control@0,name
As you see there is still much left to investigate, if somebody has some hints or wants to help you are welcome to join this thread here. Also for easing your investigation i created a small app (based on the great work of the guys at nouveau project) attached at this thread. Note it just parses the bios, it can't save any changes you make.
Also if you happen to have real macs, it would be great if you can provide us an ioreg dump and your nVidia bios.
NvidiaInfo.zip 128.65KB 1661 downloads