11 November 2006, 15:44 | #1 |
Peter
Join Date: Oct 2004
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New features in winuae
Would it be possible to document in a readme file, what new features in Winuae do?
For example, 'More Accurate FPU' on cPU page? What does this really mean? Also, what does 'Faster RTG' on Chipset page mean? There are a couple of items on Misc tab that are not self - evident either... |
11 November 2006, 16:13 | #2 |
WinUAE developer
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"Faster RTG" = disable non-needed emulation features while RTG (P96) screen is active for small speed boost. (like internal bitplane emulation, copper is replaced with "instant copper" etc..)
"Accurate FPU" = slower but more accurate (mainly improves accuracy of rounding. x86 and 68k FPUs have slightly different rounding modes, in non-accurate mode x86 rounding is used. Normally the difference is insignificant.) |
13 November 2006, 12:55 | #3 | |
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Quote:
Sorry Toni, but "Accurate FPU" is not necessarily more accurate in terms of the rounding precision and the rounding modes and precisions of the x86 and the m68k are exactly the same, just in a different bit-field order. So, what's the real intention behind this FPU option in WinUAEs GUI? I would prefer to call this switch "strict FPU emulation", because it can be used to force the JIT/FPU to do exactly what Motorola says in the 68000 Programmers Manuals about how some special FPU instructions should behave. There are two commands for the 68881 and a bunch of new special FPU instructions introduced with the 68040/60 FPU. Unlike all other normal commands these instructions have a fixed implicit rounding precision that has to be used to round the operations result independently of the actual global rounding precision, which is stored in an extra FPU register. It's the 2. time now, that this stupid editor logs me out while I'm still writing and the complete text disappeared again. For the 68881/2 the two special instructions are FSGLMUL and FSGLDIV. Both have to be executed completely with SINGLE PRECISION rounding, no matter what the actual setting for the global precision in the FPU register is. WinUAEs default behaviour is not to take care of the implicit fixed mode of these special instructions and keep the global rounding all the time, and it's of course a bit faster than switching the precision for a single command. For the 040/60 FPU there are a lot more new commands with a fixed rounding precision like FSMOVE, FSABS, FSNEG, FSADD, FSSUB, FSMUL, FSDIV and FSSQRT and with DOUBLE PRECISION it's FDMOVE, FDABS, FDNEG, FDADD, FDSUB, FDMUL, FDDIV and FDSQRT. Usually, WinUAE won't take any care of the desired rounding for the result. Without enabling this "More accurate FPU" option you will get the same as if your program had just used FMOVE, FABS, FNEG, FADD, FSUB etc instead. But, if you switch this option on, then WinUAEs FPU emulation will do exactly what Motorola wants the command to do and the result should be equal to the result of the same instruction performed with an FPU of a real Amiga. Last edited by PeterK; 13 November 2006 at 13:50. |
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13 November 2006, 13:09 | #4 | |
WinUAE developer
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JIT, Picasso96, FPU, MIDI (for example) are things I am not too interested which can explain the mistake |
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13 November 2006, 14:09 | #5 | |
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option to answer the question of pjhutch. I hope he can understand it |
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13 November 2006, 15:40 | #6 |
RIP Friends
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I’m due to update my guide site soon. Just want to check a few things before I get around to updating the site. (Sorry Peter, I’m hijacking your thread )
The ‘Automatic Switching’ tick box under Sound Properties - I take it, this disables sound when not in use during emulation, which reduces CPU load/use, and then auto enables sound when required. Should I recommend users to tick this box? Should I also recommend users to also tick the 'Faster RTG' on Chipset Properties? So, with the 'Accurate FPU' tick box, I will put this as optional and should I tell users to: Enable if they experience problems. Or should I say, enable if the program requires more accurate CPU emulation? |
13 November 2006, 17:06 | #7 |
WinUAE developer
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Generally options that are recommended are enabled by default (includes both new options)
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13 November 2006, 20:21 | #8 | |
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any problems, because on some systems the more complex FPU routines may cause a small speedloss. On my PC it was only 5%, but it can be more. |
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