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VFPU: problem with vtfm3.t

 
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davidgf



Joined: 31 Aug 2009
Posts: 22
PostPosted: Sun Sep 27, 2009 4:25 am    Post subject: VFPU: problem with vtfm3.t Reply with quote
Hello I have a problem. I'm implementing some functions in VFPU hardware but this function:

Code:

PURE_INLINE void dMULTIPLY0_331_ (dReal* vout, const dReal* mat, const dReal* v) {
       __asm__ volatile (
          "ulv.q    R000, 0+  %1\n"

          "ulv.q    R001, 16+ %1\n"
          "ulv.q    R002, 32+ %1\n"
          "ulv.q    R100, %2\n"

          "vtfm3.t  R003, M000, R100\n"

          "usv.q    R003, %0\n"
          : "+m"(vout[0]): "m"(mat[0]), "m"(v[0]));
}


does not work, but this one (which doesn't use vtfm3.t) works like a charm:

Code:


PURE_INLINE void dMULTIPLY0_331_ (dReal* vout, const dReal* mat, const dReal* v) {
       __asm__ volatile (
          "ulv.q    R000, 0+  %1\n"

          "ulv.q    R001, 16+ %1\n"
          "ulv.q    R002, 32+ %1\n"
          "ulv.q    R100, %2\n"

          "vdot.t   S003, R000, R100\n"
          "vdot.t   S013, R001, R100\n"
          "vdot.t   S023, R002, R100\n"

          "usv.q    R003, %0\n"
          : "+m"(vout[0]): "m"(mat[0]), "m"(v[0]));
}
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jsharrad



Joined: 20 Oct 2005
Posts: 102
PostPosted: Mon Sep 28, 2009 12:52 am    Post subject: Reply with quote
I read this a while back...
PLEASE READ THIS: There are 2 instructions, ulv.q and usv.q, that perform unaligned ran transfers to/from the vfpu. These have been found to be faulty so it is not recommended to use them. You have been warned.
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davidgf



Joined: 31 Aug 2009
Posts: 22
PostPosted: Mon Sep 28, 2009 7:33 am    Post subject: Reply with quote
I think this has nothing to do with the error.
The error is within the tfm and dot functions. And it's almost impossible to avoid using ulv.q function, because aligning data in the stack is quite complicated!
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hlide



Joined: 10 Sep 2006
Posts: 750
PostPosted: Thu Oct 15, 2009 6:06 am    Post subject: Reply with quote
on PSP1000, using ULV wiill scratch FPU register with the same index so if you are using VFPU register $C000 to load it from memory, you're modifying $fpr0 with the same value as $S000 as well. That's why you MUST never use ULV if you plan to keep compatibily with psp1000. The reason is ULV is mapped to MIPS64 LDC1 (FPU double load) and sony engineers probably forgot to cut off the output link to FPU registers.
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hlide



Joined: 10 Sep 2006
Posts: 750
PostPosted: Thu Oct 15, 2009 6:24 am    Post subject: Reply with quote
can you be more precise about what you get with vtfm3.t ?
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