c6f927985cf2141c464aec41d03480dbeba222a0
1 # This stage is intended to do Condition Register instructions
2 # and output, as well as carry and overflow generation.
3 # NOTE: with the exception of mtcrf and mfcr, we really should be doing
4 # the field decoding which
5 # selects which bits of CR are to be read / written, back in the
6 # decoder / insn-isue, have both self.i.cr and self.o.cr
7 # be broken down into 4-bit-wide "registers", with their
8 # own "Register File" (indexed by bt, ba and bb),
9 # exactly how INT regs are done (by RA, RB, RS and RT)
10 # however we are pushed for time so do it as *one* register.
12 from nmigen
import (Module
, Signal
, Cat
, Repl
, Mux
, Const
, Array
)
13 from nmutil
.pipemodbase
import PipeModBase
14 from soc
.cr
.pipe_data
import CRInputData
, CROutputData
15 from soc
.decoder
.power_enums
import InternalOp
17 from soc
.decoder
.power_fields
import DecodeFields
18 from soc
.decoder
.power_fieldsn
import SignalBitRange
21 class CRMainStage(PipeModBase
):
22 def __init__(self
, pspec
):
23 super().__init
__(pspec
, "main")
24 self
.fields
= DecodeFields(SignalBitRange
, [self
.i
.ctx
.op
.insn
])
25 self
.fields
.create_specs()
28 return CRInputData(self
.pspec
)
31 return CROutputData(self
.pspec
)
33 def elaborate(self
, platform
):
37 xl_fields
= self
.fields
.FormXL
38 xfx_fields
= self
.fields
.FormXFX
40 # default: cr_o remains same as cr input unless modified, below
41 cr_o
= Signal
.like(self
.i
.cr
)
42 comb
+= cr_o
.eq(self
.i
.cr
)
44 ##### prepare inputs / temp #####
46 # Generate array for cr input so bits can be selected
47 cr_arr
= Array([Signal(name
=f
"cr_arr_{i}") for i
in range(32)])
49 comb
+= cr_arr
[i
].eq(self
.i
.cr
[31-i
])
51 # Generate array for cr output so the bit to write to can be
52 # selected by a signal
53 cr_out_arr
= Array([Signal(name
=f
"cr_out_{i}") for i
in range(32)])
55 comb
+= cr_o
[31-i
].eq(cr_out_arr
[i
])
56 comb
+= cr_out_arr
[i
].eq(cr_arr
[i
])
58 # Ugh. mtocrf and mtcrf have one random bit differentiating
59 # them. This bit is not in any particular field, so this
60 # extracts that bit from the instruction
61 move_one
= Signal(reset_less
=True)
62 comb
+= move_one
.eq(self
.i
.ctx
.op
.insn
[20])
64 # crand/cror and friends get decoded to the same opcode, but
65 # one of the fields inside the instruction is a 4 bit lookup
66 # table. This lookup table gets indexed by bits a and b from
67 # the CR to determine what the resulting bit should be.
69 # Grab the lookup table for cr_op type instructions
70 lut
= Array([Signal(name
=f
"lut{i}") for i
in range(4)])
71 # There's no field, just have to grab it directly from the insn
73 comb
+= lut
[i
].eq(self
.i
.ctx
.op
.insn
[6+i
])
75 # Generate the mask for mtcrf, mtocrf, and mfocrf
76 fxm
= Signal(xfx_fields
.FXM
[0:-1].shape())
77 comb
+= fxm
.eq(xfx_fields
.FXM
[0:-1])
79 # replicate every fxm field in the insn to 4-bit, as a mask
80 mask
= Signal(32, reset_less
=True)
81 comb
+= mask
.eq(Cat(*[Repl(fxm
[i
], 4) for i
in range(8)]))
83 #################################
84 ##### main switch statement #####
86 with m
.Switch(op
.insn_type
):
88 with m
.Case(InternalOp
.OP_MCRF
):
89 # MCRF copies the 4 bits of crA to crB (for instance
93 print ("xl", xl_fields
)
94 bf
= Signal(xl_fields
.BF
[0:-1].shape())
95 comb
+= bf
.eq(xl_fields
.BF
[0:-1])
97 bfa
= Signal(xl_fields
.BFA
[0:-1].shape())
98 comb
+= bfa
.eq(xl_fields
.BFA
[0:-1])
101 comb
+= cr_out_arr
[bf
*4 + i
].eq(cr_arr
[bfa
*4 + i
])
103 ##### crand, cror, crnor etc. #####
104 with m
.Case(InternalOp
.OP_CROP
):
105 # Get the bit selector fields from the instruction
106 bt
= Signal(xl_fields
.BT
[0:-1].shape())
107 ba
= Signal(xl_fields
.BA
[0:-1].shape())
108 bb
= Signal(xl_fields
.BB
[0:-1].shape())
109 comb
+= bt
.eq(xl_fields
.BT
[0:-1])
110 comb
+= ba
.eq(xl_fields
.BA
[0:-1])
111 comb
+= bb
.eq(xl_fields
.BB
[0:-1])
113 # Use the two input bits to look up the result in the LUT
114 comb
+= cr_out_arr
[bt
].eq(lut
[Cat(cr_arr
[bb
], cr_arr
[ba
])])
117 with m
.Case(InternalOp
.OP_MTCRF
):
118 # mtocrf and mtcrf are essentially identical
119 # put input (RA) - mask-selected - into output CR, leave
121 comb
+= cr_o
.eq((self
.i
.a
[0:32] & mask
) |
(self
.i
.cr
& ~mask
))
124 with m
.Case(InternalOp
.OP_MFCR
):
127 comb
+= self
.o
.o
.eq(self
.i
.cr
& mask
)
130 comb
+= self
.o
.o
.eq(self
.i
.cr
)
133 comb
+= self
.o
.cr
.eq(cr_o
)
134 comb
+= self
.o
.ctx
.eq(self
.i
.ctx
)