netwinder-fpe.rst (6215B)
1============= 2Current State 3============= 4 5The following describes the current state of the NetWinder's floating point 6emulator. 7 8In the following nomenclature is used to describe the floating point 9instructions. It follows the conventions in the ARM manual. 10 11:: 12 13 <S|D|E> = <single|double|extended>, no default 14 {P|M|Z} = {round to +infinity,round to -infinity,round to zero}, 15 default = round to nearest 16 17Note: items enclosed in {} are optional. 18 19Floating Point Coprocessor Data Transfer Instructions (CPDT) 20------------------------------------------------------------ 21 22LDF/STF - load and store floating 23 24<LDF|STF>{cond}<S|D|E> Fd, Rn 25<LDF|STF>{cond}<S|D|E> Fd, [Rn, #<expression>]{!} 26<LDF|STF>{cond}<S|D|E> Fd, [Rn], #<expression> 27 28These instructions are fully implemented. 29 30LFM/SFM - load and store multiple floating 31 32Form 1 syntax: 33<LFM|SFM>{cond}<S|D|E> Fd, <count>, [Rn] 34<LFM|SFM>{cond}<S|D|E> Fd, <count>, [Rn, #<expression>]{!} 35<LFM|SFM>{cond}<S|D|E> Fd, <count>, [Rn], #<expression> 36 37Form 2 syntax: 38<LFM|SFM>{cond}<FD,EA> Fd, <count>, [Rn]{!} 39 40These instructions are fully implemented. They store/load three words 41for each floating point register into the memory location given in the 42instruction. The format in memory is unlikely to be compatible with 43other implementations, in particular the actual hardware. Specific 44mention of this is made in the ARM manuals. 45 46Floating Point Coprocessor Register Transfer Instructions (CPRT) 47---------------------------------------------------------------- 48 49Conversions, read/write status/control register instructions 50 51FLT{cond}<S,D,E>{P,M,Z} Fn, Rd Convert integer to floating point 52FIX{cond}{P,M,Z} Rd, Fn Convert floating point to integer 53WFS{cond} Rd Write floating point status register 54RFS{cond} Rd Read floating point status register 55WFC{cond} Rd Write floating point control register 56RFC{cond} Rd Read floating point control register 57 58FLT/FIX are fully implemented. 59 60RFS/WFS are fully implemented. 61 62RFC/WFC are fully implemented. RFC/WFC are supervisor only instructions, and 63presently check the CPU mode, and do an invalid instruction trap if not called 64from supervisor mode. 65 66Compare instructions 67 68CMF{cond} Fn, Fm Compare floating 69CMFE{cond} Fn, Fm Compare floating with exception 70CNF{cond} Fn, Fm Compare negated floating 71CNFE{cond} Fn, Fm Compare negated floating with exception 72 73These are fully implemented. 74 75Floating Point Coprocessor Data Instructions (CPDT) 76--------------------------------------------------- 77 78Dyadic operations: 79 80ADF{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - add 81SUF{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - subtract 82RSF{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse subtract 83MUF{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - multiply 84DVF{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - divide 85RDV{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse divide 86 87These are fully implemented. 88 89FML{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - fast multiply 90FDV{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - fast divide 91FRD{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - fast reverse divide 92 93These are fully implemented as well. They use the same algorithm as the 94non-fast versions. Hence, in this implementation their performance is 95equivalent to the MUF/DVF/RDV instructions. This is acceptable according 96to the ARM manual. The manual notes these are defined only for single 97operands, on the actual FPA11 hardware they do not work for double or 98extended precision operands. The emulator currently does not check 99the requested permissions conditions, and performs the requested operation. 100 101RMF{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - IEEE remainder 102 103This is fully implemented. 104 105Monadic operations: 106 107MVF{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - move 108MNF{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - move negated 109 110These are fully implemented. 111 112ABS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - absolute value 113SQT{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - square root 114RND{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - round 115 116These are fully implemented. 117 118URD{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - unnormalized round 119NRM{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - normalize 120 121These are implemented. URD is implemented using the same code as the RND 122instruction. Since URD cannot return a unnormalized number, NRM becomes 123a NOP. 124 125Library calls: 126 127POW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - power 128RPW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse power 129POL{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - polar angle (arctan2) 130 131LOG{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base 10 132LGN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base e 133EXP{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - exponent 134SIN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - sine 135COS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - cosine 136TAN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - tangent 137ASN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arcsine 138ACS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arccosine 139ATN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arctangent 140 141These are not implemented. They are not currently issued by the compiler, 142and are handled by routines in libc. These are not implemented by the FPA11 143hardware, but are handled by the floating point support code. They should 144be implemented in future versions. 145 146Signalling: 147 148Signals are implemented. However current ELF kernels produced by Rebel.com 149have a bug in them that prevents the module from generating a SIGFPE. This 150is caused by a failure to alias fp_current to the kernel variable 151current_set[0] correctly. 152 153The kernel provided with this distribution (vmlinux-nwfpe-0.93) contains 154a fix for this problem and also incorporates the current version of the 155emulator directly. It is possible to run with no floating point module 156loaded with this kernel. It is provided as a demonstration of the 157technology and for those who want to do floating point work that depends 158on signals. It is not strictly necessary to use the module. 159 160A module (either the one provided by Russell King, or the one in this 161distribution) can be loaded to replace the functionality of the emulator 162built into the kernel.