1 """IEEE Floating Point Divider Pipeline
3 Relevant bugreport: http://bugs.libre-riscv.org/show_bug.cgi?id=99
7 scnorm - FPDIVSpecialCasesDeNorm ispec FPADDBaseData
10 StageChain: FPDIVSpecialCasesMod,
13 pipediv0 - FPDivStagesSetup ispec FPSCData
14 -------- ospec DivPipeInterstageData
16 StageChain: FPDivStage0Mod,
18 DivPipeCalculateStage,
22 pipediv1 - FPDivStagesIntermediate ispec DivPipeInterstageData
23 -------- ospec DivPipeInterstageData
25 StageChain: DivPipeCalculateStage,
31 pipediv5 - FPDivStageFinal ispec FPDivStage0Data
32 -------- ospec FPAddStage1Data
34 StageChain: DivPipeCalculateStage,
36 DivPipeCalculateStage,
40 normpack - FPNormToPack ispec FPAddStage1Data
41 -------- ospec FPPackData
43 StageChain: Norm1ModSingle,
48 the number of combinatorial StageChains (n_comb_stages) in
49 FPDivStages is an argument arranged to get the length of the whole
50 pipeline down to sane numbers.
52 the reason for keeping the number of stages down is that for every
53 pipeline clock delay, a corresponding ReservationStation is needed.
54 if there are 24 pipeline stages, we need a whopping TWENTY FOUR
55 RS's. that's far too many. 6 is just about an acceptable number.
56 even 8 is starting to get alarmingly high.
59 from nmigen
import Module
60 from nmigen
.cli
import main
, verilog
62 from nmutil
.singlepipe
import ControlBase
63 from nmutil
.concurrentunit
import ReservationStations
, num_bits
65 from ieee754
.fpcommon
.getop
import FPADDBaseData
66 from ieee754
.fpcommon
.denorm
import FPSCData
67 from ieee754
.fpcommon
.fpbase
import FPFormat
68 from ieee754
.fpcommon
.pack
import FPPackData
69 from ieee754
.fpcommon
.normtopack
import FPNormToPack
70 from ieee754
.fpdiv
.specialcases
import FPDIVSpecialCasesDeNorm
71 from ieee754
.fpdiv
.divstages
import (FPDivStagesSetup
,
72 FPDivStagesIntermediate
,
74 from ieee754
.pipeline
import PipelineSpec
75 from ieee754
.div_rem_sqrt_rsqrt
.core
import DivPipeCoreConfig
78 class FPDIVBasePipe(ControlBase
):
79 def __init__(self
, pspec
):
81 ControlBase
.__init
__(self
)
84 max_n_comb_stages
= 2 # TODO (depends on how many RS's we want)
85 # to which the answer: "as few as possible"
86 # is required. too many ReservationStations
87 # means "big problems".
89 # XXX BUG - subtracting 4 from number of stages stops assert
90 # probably related to having to add 4 in FPDivMuxInOut
91 radix
= pspec
.log2_radix
92 n_stages
= pspec
.core_config
.n_stages
// max_n_comb_stages
95 for i
in range(n_stages
):
97 n_comb_stages
= max_n_comb_stages
98 # needs to convert input from pipestart ospec
100 kls
= FPDivStagesSetup
101 #n_comb_stages -= 1 # reduce due to work done at start?
103 # needs to convert output to pipeend ispec
104 elif i
== n_stages
- 1:
105 kls
= FPDivStagesFinal
106 #n_comb_stages -= 1 # FIXME - reduce due to work done at end?
110 kls
= FPDivStagesIntermediate
112 pipechain
.append(kls(self
.pspec
, n_comb_stages
, stage_idx
))
113 stage_idx
+= n_comb_stages
# increment so that each CalcStage
114 # gets a (correct) unique index
116 self
.pipechain
= pipechain
118 # start and end: unpack/specialcases then normalisation/packing
119 self
.pipestart
= pipestart
= FPDIVSpecialCasesDeNorm(self
.pspec
)
120 self
.pipeend
= pipeend
= FPNormToPack(self
.pspec
)
122 self
._eqs
= self
.connect([pipestart
] + pipechain
+ [pipeend
])
124 def elaborate(self
, platform
):
125 m
= ControlBase
.elaborate(self
, platform
)
128 m
.submodules
.scnorm
= self
.pipestart
129 for i
, p
in enumerate(self
.pipechain
):
130 setattr(m
.submodules
, "pipediv%d" % i
, p
)
131 m
.submodules
.normpack
= self
.pipeend
133 # ControlBase.connect creates the "eqs" needed to connect each pipe
134 m
.d
.comb
+= self
._eqs
139 return x
if x
% mod
== 0 else x
+ mod
- x
% mod
141 class FPDIVMuxInOut(ReservationStations
):
142 """ Reservation-Station version of FPDIV pipeline.
144 * fan-in on inputs (an array of FPADDBaseData: a,b,mid)
145 * N-stage divider pipeline
146 * fan-out on outputs (an array of FPPackData: z,mid)
148 Fan-in and Fan-out are combinatorial.
150 :op_wid: - set this to the width of an operator which can
151 then be used to change the behaviour of the pipeline.
154 def __init__(self
, width
, num_rows
, op_wid
=0):
155 self
.id_wid
= num_bits(width
)
156 self
.pspec
= PipelineSpec(width
, self
.id_wid
, op_wid
)
157 # get the standard mantissa width, store in the pspec HOWEVER...
158 fmt
= FPFormat
.standard(width
)
161 # ...4 extra bits on the mantissa: MSB is zero, MSB-1 is 1
162 # then there is guard and round at the LSB end.
163 # also: round up to nearest radix
164 fmt
.m_width
= roundup(fmt
.m_width
+ 4, log2_radix
)
166 cfg
= DivPipeCoreConfig(fmt
.m_width
, 0*fmt
.fraction_width
, log2_radix
)
168 self
.pspec
.fpformat
= fmt
169 self
.pspec
.log2_radix
= log2_radix
170 self
.pspec
.core_config
= cfg
172 # XXX TODO - a class (or function?) that takes the pspec (right here)
173 # and creates... "something". that "something" MUST have an eq function
174 # new_pspec = deepcopy(self.pspec)
175 # new_pspec.opkls = DivPipeCoreOperation
176 # self.alu = FPDIVBasePipe(new_pspec)
177 self
.alu
= FPDIVBasePipe(self
.pspec
)
178 ReservationStations
.__init
__(self
, num_rows
)
181 return FPADDBaseData(self
.pspec
)
184 return FPPackData(self
.pspec
)