P33 SetDrawTPage

00023ebc: 27bdffd8 addiu r29,r29,0xffd8
00023ec0: afb3001c sw r19,0x001c(r29)
00023ec4: 00809821 addu r19,r4,r0                   # pointer to primative
00023ec8: afb20018 sw r18,0x0018(r29)
00023ecc: 00a09021 addu r18,r5,r0                   # drawing to display area
00023ed0: afb00010 sw r16,0x0010(r29)
00023ed4: 00c08021 addu r16,r6,r0                   # dither processing flag
00023ed8: afb10014 sw r17,0x0014(r29)
00023edc: 00e08821 addu r17,r7,r0                   # tpage to draw
00023ee0: 34020001 ori r2,r0,0x0001
00023ee4: afbf0020 sw r31,0x0020(r29)
00023ee8: 0c00916f jal 0x000245bc                   # ? Accessor (0x245bc) <- configuration of VRAM? 1,2 = 2mb, 3 = < 1mb?
00023eec: a2620003 sb r2,0x0003(r19)
00023ef0: 34030001 ori r3,r0,0x0001
00023ef4: 10430006 beq r2,r3,0x00023f10             # branch never (fft value = 3)
00023ef8: 00000000 nop
00023efc: 0c00916f jal 0x000245bc
00023f00: 00000000 nop
00023f04: 34030002 ori r3,r0,0x0002
00023f08: 14430009 bne r2,r3,0x00023f30             # branch always (fft value = 3)
00023f0c: 00000000 nop
00023f10: 12000002 beq r16,r0,0x00023f1c
00023f14: 3c03e100 lui r3,0xe100
00023f18: 34630800 ori r3,r3,0x0800                 # only set if VRAM = 2MB [[1]], texture page y in base 2
00023f1c: 12400002 beq r18,r0,0x00023f28
00023f20: 322227ff andi r2,r17,0x27ff
00023f24: 34421000 ori r2,r2,0x1000
00023f28: 08008fd3 j 0x00023f4c
00023f2c: 00621025 or r2,r3,r2

the part that matters:
00023f30: 12000002 beq r16,r0,0x00023f3c
00023f34: 3c07e100 lui r7,0xe100                    # drawmode instruction
00023f38: 34e70200 ori r7,r7,0x0200                 # dither 24bit -> 15bit
00023f3c: 12400002 beq r18,r0,0x00023f48            # branch if not drawing to display area
00023f40: 322209ff andi r2,r17,0x09ff               # retain most Tpage flags
00023f44: 34420400 ori r2,r2,0x0400                 # else, set draw to display area
00023f48: 00e21025 or r2,r7,r2                      # bit-combine
00023f4c: ae620004 sw r2,0x0004(r19)                # store drawmode = texturepage
00023f50: 8fbf0020 lw r31,0x0020(r29)
00023f54: 8fb3001c lw r19,0x001c(r29)
00023f58: 8fb20018 lw r18,0x0018(r29)
00023f5c: 8fb10014 lw r17,0x0014(r29)
00023f60: 8fb00010 lw r16,0x0010(r29)
00023f64: 27bd0028 addiu r29,r29,0x0028
00023f68: 03e00008 jr r31
00023f6c: 00000000 nop