This is an attempt to explain the i8xx registers. It was started for the i830, and bits of information about the other models was unsystematically added. Please extend as appropriate, and mark the differences.
The i830 emulates two PCI cards. The register of the PCI cards seem to shadow each other, and the X driver only uses the first card.
There are several parts used for graphic output:
Display planes A,B,C --> Pipes A,B --> Analog/Digital Ports I2C control for TV encoder.
Some registers may be double buffered, and may need a write to another register to commit.
Here are some definitions from the i845G data sheet:
A PLANE consists of a rectangular shaped image that has characteristics such as source, size, position, method, and format. These planes get attached to source surfaces that are rectangular memory surfaces with a similar set of characteristics. They are also associated with a destination pipe.
A PIPE consists of a set of combined planes and a timing generator.
|Chipset||I2C lines||Known TV|
|i810||DDC; LTV||GPIOB = LTV|
|i830||DDC1, I2C, DDC2; M_DDC, M_I2C||GPIOC = M_I2C|
|i845||DDC_A; MI2C, MDVI, MDDC||GPIOE|
|i865||DDC_A; MI2C, MDVI, MDDC||GPIOE = M_I2C|
On the i830, DVO port A uses DDC2 or I2C, DVO ports B/C use M_I2C or M_DDC. The DDC ports are used for EDID display information transfer from the monitor (typically at address 0xA0) or flat panel. On the I2C port a device at 0x04 has been observed, possibly a flat panel controller.
|0x05010||GPIOA General purpose I/O A, one of the DDC ports.|
|0x05014||GPIOB General purpose I/O B, I2C port.|
|0x05018||GPIOC General purpose I/O C, M_I2C port.|
|0x05020||GPIOE General purpose I/O E (for i845)|
|0x05024||GPIOF General purpose I/O F (for i???)|
|12||GPIO1 data in|
|11||GPIO1 data value|
|10||GPIO1 data mask (1=write data)|
|GPIO1 direction value (0=input, 1=output)|
|GPIO1 direction mask (1=write direction)|
|GPIO0 data in|
|GPIO0 data value|
|GPIO0 data mask|
|GPIO0 direction value|
|GPIO0 direction mask|
GPIO1 is the data pin, GPIO0 is the clock pin. Maybe there are even more GPIO registers?
The i865 implements a hardware GMBus controller that can be used to control these signals. This allows higher speed transactions (up to 400 kHz) on theses lines than was allowed with previous software centric `bit-bashing' techniques.
It is not completely clear how the GMBus controller registers work.
There are (at least) 3 display planes:
A: primary display plane
B: 'sprite' plane (for specific laptop display information?)
C: overlay plane (can also be directly sent in YUV format to DVO)
The datasheet diagram shows overlay, sprite, two cursor, and primary and secondary display units. Maybe those correspond to the planes. The datasheet also meantions a popup plane for mobile applications. The single overlay plane can only displayed on "single-pipe simultanious displays" for multi-monitors. (For the i810, 0x70008 PIXCONF has some of the functions used here.) For the i865, these registers seem to be somewhere else.
|0x70180||DSPACTRL Display plane A control|
|0x71180||DSPBCTRL Display plane B control|
|31||plane enable (1=enabled)|
|30||gamma correction enable (0=bypass, 1=enabled)|
|29:26||pixformat (2=8BPP, 4=15_16BPP, 5=16BPP, 6=32BPP_NO_ALPHA, 7=32BPP)|
|25||stereo enable (1=enabled)|
|24||select pipe (0=A, 1=B)|
|22||source key enable (1=enabled)|
|21:20||pixel multiplicity (0=normal, 1=doubleline, 2=3=reserved)|
|18||stereo polarity (0=first, 1=second)|
|15||alpha transfer mode (1=enabled) ; B only|
|sprite_above (0=display A, 1=overlay) ; B only|
Note: 8BPP is indexed, 15_16BPP is 5-5-5, 16BPP is 5-6-5, 32BPP_NO_ALPHA is X:8:8:8, and 32BPP is 8:8:8:8.
Note: Stereo requires two start (base) addresses, at least for plane B.
It is not clear why a display plane has to connect to a pipe, instead of the other way round, unless the plane block also contains the counters.
|0x70184||DSPABASE Display plane A base address||0x71184||DSPBBASE Display plane B base address|
|0x70188||DSPASTRIDE Display plane A stride (= pitch)||0x71188||DSPBSTRIDE Display plane B stride (= pitch)||<)>31-16||UNKNOWN, 15CF/0001||<)> ?- 0||stride|
There are two pipes, which control the timing.
|26:16||horizontal (= HTOTAL displayed)|
|10: 0||vertical (= VTOTAL displayed)|
|0x60020||BCLRPAT border color pattern|
Identical registers for pipe B are at 0x61000-0x61020.
On the i810, there also was the LCDTV_C register, which is probably not any longer supported.
|0x60018||LCDTV_C LCD/TV-Out control register|
|0x70008||PIPEACONF (PIXCONF for i810)|
|30||width (1=double, 0=single)|
|25||lock (1=locked) ; unclear|
|0x71400||UNKNOWN (= 0020008e)|
There are three dedicated Digital Video Ports and one Analog Port. DVOB and C are multixplexed with the AGP pins. The local flat panel (LFP) is normally connected to DVOA. DVOB and DVOC may be combined into one 24bit wide port. DVO port signals are:
|CLK/CLK#||differental clock output up to 165 MHz|
|HSYNC||outgoing HSync with programmable polarity|
|VSYNC||outgoing VSync with programmable polarity|
|BLANK#||outgoing blank period or border period signal|
|INTR||incoming interrupt (DVOA and DVOBC)|
|CLKINT||incoming clock or second interrupt (DVOA and DVOBC)|
|FLD/STL||incoming TV field (to synchronize overlay) or FP stall signal|
The DPLL registers control the phase locked loops that convert the incoming to the outgoing clock, or possibly some internal clock to the outgoing clock. They are associated to the corresponding pipe.
|31||VCO enable (=1 for TFT, TV, mon)|
|30||2X clock enable (=1 for TFT, TV; =0 for mon)|
|29||synclock enable (=0)|
|28||VGA mode disable (=1 for TFT, TV, mon; =0 mon)|
|24||[i???] PLL divisor select|
|23||P2 post divisor (loop divide flag?)|
|21||P1 force DIV2|
|20:16||P1 post divisor|
|14:13||reference select (=0 for LCD/mon, =2 for TV ?)|
|[i???] rate select mask (0=fp0, 1=fp1)|
There seems to be additional PLLs for the flat panel. (FIXME: Dave, please add a detailed explanation).
|0x06040||FPA0 flat panel PLL A0|
|0x06044||FPA1 flat panel PLL A1|
|0x06048||FPB0 flat panel PLL B0|
|0x0604C||FPB1 flat panel PLL B1|
where M = 5*(M1+2) + (M2+2), and Clk = RefCLK * M / (N+2) / P
The ADPA register controls the analog output (monitor).
|31||DAC enable (1=enabled) (=monitor enabled)|
|30||Pipe select (0=A, 1=B) [maybe doesn't work]|
|15||Use_VGA_HVPolarity (0=Sets HVPolarity)|
|11||VSync control disable (1=disabled)|
|10||HSync control disable (1=disabled)|
|VSync active (0=low, 1=high)|
|HSync active (0=low, 1=high)|
For the 3 DVO ports, only the enable bit is known. Other bits may include interrupt handling, polarity control for blank and sync signals, configuration of clock vs. second interrupt and field vs. stall.
|31||DVO enable (1=enabled)|
|30||Pipe select (guess!) (0=A, 1=B)|
This is used in i855 instead of DVO.
|0x61180||LVDS meaning unknown|
|23:12||(not needed ?)|
|11: 0||(not needed ?)|
FIXME: What about 0x61104 ADPA_SRCDIM? and 0x61184 LVDS_SRCDIM? Maybe used for centering?
|0x020cc||UNKNOWN = 000c000c / 0000004c|
There are now two watermark registers, with a format different from the I810 FW_BLC register.
|0x020d8||Watermark/Burst = 01080108|
|0x020dc||Watermark/Burst = 00000108|
|11: 8||Burst A|
Software Flags (= scratch registers):
|0x71414||SWF1 (amount of video memory available)|