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[Docs] Add more notes on the single-page offset

This commit is contained in:
DrChat 2018-02-17 10:33:34 -06:00
parent 3d1c2a6c9a
commit 705fd7594a
1 changed files with 12 additions and 1 deletions
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13
docs/cpu.md
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@ -95,7 +95,18 @@ i.e. virtual 0xA0000000 == physical 0x00000000
Unfortunately, the 0xE0000000-0xFFFFFFFF range is unused in Xenia because
it maps to physical memory with a single page offset, which is impossible
to do under the Win32 API.
to do under the Win32 API. We can't fake this either, as this offset is
built into games - see the following sequence:
```
srwi r9, r10, 20 # r9 = r10 >> 20
clrlwi r10, r10, 3 # r10 = r10 & 0x1FFFFFFF (physical address)
addi r11, r9, 0x200
rlwinm r11, r11, 0,19,19 # r11 = r11 & 0x1000
add r11, r11, r10 # add 1 page to addresses > 0xE0000000
# r11 = addess passed to GPU
```
## Memory Management