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Interpreter_SystemRegisters: Handle mtspr to HID1 and PVR properly

Despite both being documented as read-only registers, only one of them
is truly read-only. An mtspr to HID1 will steamroll bits 0-4 with
bits 0-4 of whatever value is currently in the source register, the rest
of the bits are not modified as bits 5-31 are considered reserved, so
these ignore writes to them.

PVR on the other hand, is truly a read-only register. Attempts to write
to it don't modify the value within it, so we model this behavior.
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lioncash committed Jun 20, 2018
1 parent bdfc6de commit d0fbba9ac1f23f6d55e8d18d8d24bc24220596d8
Showing with 13 additions and 0 deletions.
  1. +13 −0 Source/Core/Core/PowerPC/Interpreter/Interpreter_SystemRegisters.cpp
@@ -312,6 +312,11 @@ void Interpreter::mtspr(UGeckoInstruction inst)
SystemTimers::TimeBaseSet();
break;
case SPR_PVR:
// PVR is a read-only register so maintain its value.
rSPR(index) = old_value;
break;
case SPR_HID0: // HID0
{
UReg_HID0 old_hid0;
@@ -334,6 +339,14 @@ void Interpreter::mtspr(UGeckoInstruction inst)
}
}
break;
case SPR_HID1:
// Despite being documented as a read-only register, it actually isn't. Bits
// 0-4 (27-31 from a little endian perspective) are modifiable. The rest are not
// affected, as those bits are reserved and ignore writes to them.
rSPR(index) &= 0xF8000000;
break;
case SPR_HID2: // HID2
// TODO: generate illegal instruction for paired inst if PSE or LSQE
// not set.

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