Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) TODO LIST
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) =========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) ::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6)   POW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - power
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7)   RPW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse power
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8)   POL{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - polar angle (arctan2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10)   LOG{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base 10
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)   LGN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base e
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)   EXP{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - exponent
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13)   SIN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - sine
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14)   COS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - cosine
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)   TAN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - tangent
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16)   ASN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arcsine
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)   ACS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arccosine
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18)   ATN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arctangent
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) These are not implemented.  They are not currently issued by the compiler,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) and are handled by routines in libc.  These are not implemented by the FPA11
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) hardware, but are handled by the floating point support code.  They should
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) be implemented in future versions.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) There are a couple of ways to approach the implementation of these.  One
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) method would be to use accurate table methods for these routines.  I have
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) a couple of papers by S. Gal from IBM's research labs in Haifa, Israel that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) seem to promise extreme accuracy (in the order of 99.8%) and reasonable speed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) These methods are used in GLIBC for some of the transcendental functions.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) Another approach, which I know little about is CORDIC.  This stands for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) Coordinate Rotation Digital Computer, and is a method of computing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) transcendental functions using mostly shifts and adds and a few
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) multiplications and divisions.  The ARM excels at shifts and adds,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) so such a method could be promising, but requires more research to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) determine if it is feasible.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) Rounding Methods
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) ----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) The IEEE standard defines 4 rounding modes.  Round to nearest is the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) default, but rounding to + or - infinity or round to zero are also allowed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) Many architectures allow the rounding mode to be specified by modifying bits
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) in a control register.  Not so with the ARM FPA11 architecture.  To change
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) the rounding mode one must specify it with each instruction.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) This has made porting some benchmarks difficult.  It is possible to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) introduce such a capability into the emulator.  The FPCR contains
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) bits describing the rounding mode.  The emulator could be altered to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) examine a flag, which if set forced it to ignore the rounding mode in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) the instruction, and use the mode specified in the bits in the FPCR.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) This would require a method of getting/setting the flag, and the bits
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) in the FPCR.  This requires a kernel call in ArmLinux, as WFC/RFC are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) supervisor only instructions.  If anyone has any ideas or comments I
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) would like to hear them.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) NOTE:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)  pulled out from some docs on ARM floating point, specifically
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60)  for the Acorn FPE, but not limited to it:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62)  The floating point control register (FPCR) may only be present in some
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63)  implementations: it is there to control the hardware in an implementation-
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64)  specific manner, for example to disable the floating point system.  The user
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65)  mode of the ARM is not permitted to use this register (since the right is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66)  reserved to alter it between implementations) and the WFC and RFC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67)  instructions will trap if tried in user mode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69)  Hence, the answer is yes, you could do this, but then you will run a high
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70)  risk of becoming isolated if and when hardware FP emulation comes out
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) 		-- Russell.