Difference between revisions of "Hardware/GX/Blitting Processor"

Revision as of 02:39, 21 March 2009

The Blitting Processor is a component of the Wii's GX subsystem. It is responsible for copying the EFB to the XFB, doing the RGBA->YCbCr conversion and scaling/antialiasing in the process.

BP (blitting processor) registers

The BP registers are accessed by writing a 8-bit value of 0x61 to the FIFO, followed by 32 bit value. This value is a bit weird - the high 8 bits are the register, and the low 24 bits are the register value.

EFB source registers

One can specify which part of the EFB is copied to the XFB or texture, using the following BP registers:

GX_BP_EFB_BOXCOORD (0x49)
	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Access	U				R/W										R/W
Field					Y										X

0x49: coordinates to top left of rectangle in EFB that will be copied (packed format, unknown)

GX_BP_EFB_BOXSIZE (0x4a)
	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Access	U				R/W										R/W
Field					height-1										width-1

0x4a: width and height-1 of rectangle to copy in EFB (again, unknown packed format)

XFB destination registers

The destination of the copy in the XFB is specified by the physical address of the XFB and the row stride (basically width of row, but no scaling appled).

GX_BP_XFB_ADDR (0x4B)
	230
Access	R/W

0x4b: Address of destination (XFB). BEWARE: Address is a PHYSICAL address, SHIFTED RIGHT by 5.

GX_BP_XFB_STRIDE (0x4D)
	2310	90
Access	U	R/W

0x4d: Low 10 bits specify row stride of destination.

Copy control register

GX_BP_COPY_CONTROL (0x52)
	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16
Access	U								U
Field	(register)
	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Access	U		W		R/W	U
Field			Begin copy		Clear enable

0x52: This register starts a copy. Important bits:

 * bit 10: Clear enable flag
 * bits 12-15: Set all to 1 to enable a copy.

Copy filter registers

Registers 0x01-0x04 are used for tricks like antialiasing. For a plain copy (i.e. no antialiasing) set all for to 0x666666.

Beginning a copy

The following must take place to do a copy:

Setup clear and z clear registers (optional)
Set source and destination registers
Write to display copy control register to begin a copy
Set clear, z, and control registers again (what? doubt necessary, libogc GX is stupid)

@@ Line 20: / Line 20: @@
 The destination of the copy in the XFB is specified by the '''physical''' address of the XFB and the row stride (basically width of row, but no scaling appled).
 {{regsimple | GX_BP_XFB_ADDR | addr=0x4B | bits=24 | access = R/W}}
-* 0x4b: Address of destination (XFB). BEWARE: You only have 24 bits, which means your XFB must reside somewhere in the low 16MiB of RAM.
+* 0x4b: Address of destination (XFB). BEWARE: Address is a PHYSICAL address, SHIFTED RIGHT by 5.
 {{regsimple2 | GX_BP_XFB_STRIDE | addr=0x4D | bits=24 | split=10 | access = R/W}}
 * 0x4d: Low 10 bits specify row stride of destination.