3 functions for the relationship between regspecs and Decode2Execute1Type
5 these functions encodes the understanding (relationship) between
6 Regfiles, Computation Units, and the Power ISA Decoder (PowerDecoder2).
8 based on the regspec, which contains the register file name and register
9 name, return a tuple of:
11 * how the decoder should determine whether the Function Unit needs
12 access to a given Regport or not
13 * which Regfile number on that port should be read to get that data
14 * when it comes to writing: likewise, which Regfile num should be written
16 Note that some of the port numbering encoding is *unary*. in the case
17 of "Full Condition Register", it's a full 8-bit mask of read/write-enables.
18 This actually matches directly with the XFX field in MTCR, and at
19 some point that 8-bit mask from the instruction could actually be passed
20 directly through to full_cr (TODO).
22 For the INT and CR numbering, these are expressed in binary in the
23 instruction and need to be converted to unary (1<<read_reg1.data).
24 Note however that XFX in MTCR is unary-masked!
26 XER regs are implicitly-encoded (hard-coded) based on whether the
27 operation has carry or overflow.
29 FAST regfile is, again, implicitly encoded, back in PowerDecode2, based
30 on the type of operation (see DecodeB for an example, where fast_out
31 is set, then carried into read_fast2 in PowerDecode2).
33 The SPR regfile on the other hand is *binary*-encoded, and, furthermore,
34 has to be "remapped" to internal SPR Enum indices (see SPRMap in PowerDecode2)
35 see https://libre-soc.org/3d_gpu/architecture/regfile/ section on regspecs
37 from nmigen
import Const
38 from soc
.regfile
.regfiles
import XERRegs
, FastRegs
, StateRegs
39 from soc
.decoder
.power_enums
import CryIn
42 def regspec_decode_read(e
, regfile
, name
):
43 """regspec_decode_read
49 # Int register numbering is *unary* encoded
51 return e
.read_reg1
.ok
, e
.read_reg1
.data
53 return e
.read_reg2
.ok
, e
.read_reg2
.data
55 return e
.read_reg3
.ok
, e
.read_reg3
.data
60 # CRRegs register numbering is *unary* encoded
61 if name
== 'full_cr': # full CR (from FXM field)
62 return e
.do
.read_cr_whole
.ok
, e
.do
.read_cr_whole
.data
63 if name
== 'cr_a': # CR A
64 return e
.read_cr1
.ok
, 1<<(7-e
.read_cr1
.data
)
65 if name
== 'cr_b': # CR B
66 return e
.read_cr2
.ok
, 1<<(7-e
.read_cr2
.data
)
67 if name
== 'cr_c': # CR C
68 return e
.read_cr3
.ok
, 1<<(7-e
.read_cr3
.data
)
73 # XERRegs register numbering is *unary* encoded
78 # SO needs to be read for overflow *and* for creation
79 # of CR0 and also for MFSPR
80 return ((e
.do
.oe
.oe
[0] & e
.do
.oe
.oe_ok
) | e
.xer_in |
81 (e
.do
.rc
.rc
& e
.do
.rc
.ok
)), SO
83 return (e
.do
.oe
.oe
[0] & e
.do
.oe
.oe_ok
) | e
.xer_in
, OV
85 return (e
.do
.input_carry
== CryIn
.CA
.value
) | e
.xer_in
, CA
89 if regfile
== 'STATE':
90 # STATE register numbering is *unary* encoded
93 if name
in ['cia', 'nia']:
94 return Const(1), PC
# TODO: detect read-conditions
96 return Const(1), MSR
# TODO: detect read-conditions
100 if regfile
== 'FAST':
101 # FAST register numbering is *unary* encoded
103 return e
.read_fast1
.ok
, e
.read_fast1
.data
105 return e
.read_fast2
.ok
, e
.read_fast2
.data
110 # SPR register numbering is *binary* encoded
112 return e
.read_spr1
.ok
, e
.read_spr1
.data
114 assert False, "regspec not found %s %s" % (regfile
, name
)
117 def regspec_decode_write(e
, regfile
, name
):
118 """regspec_decode_write
124 # Int register numbering is *unary* encoded
126 return e
.write_reg
, e
.write_reg
.data
127 if name
== 'o1': # RA (update mode: LD/ST EA)
128 return e
.write_ea
, e
.write_ea
.data
133 # CRRegs register numbering is *unary* encoded
134 # *sigh*. numbering inverted on part-CRs. because POWER.
135 if name
== 'full_cr': # full CR (from FXM field)
136 return e
.do
.write_cr_whole
.ok
, e
.do
.write_cr_whole
.data
137 if name
== 'cr_a': # CR A
138 return e
.write_cr
, 1<<(7-e
.write_cr
.data
)
143 # XERRegs register numbering is *unary* encoded
148 return e
.xer_out
, SO
# hmmm
150 return e
.xer_out
, OV
# hmmm
152 return e
.xer_out
, CA
# hmmm
156 if regfile
== 'STATE':
157 # STATE register numbering is *unary* encoded
159 MSR
= 1<<StateRegs
.MSR
160 if name
in ['cia', 'nia']:
161 return None, PC
# hmmm
163 return None, MSR
# hmmm
167 if regfile
== 'FAST':
168 # FAST register numbering is *unary* encoded
170 return e
.write_fast1
, e
.write_fast1
.data
172 return e
.write_fast2
, e
.write_fast2
.data
177 # SPR register numbering is *binary* encoded
178 if name
== 'spr1': # SPR1
179 return e
.write_spr
, e
.write_spr
.data
181 assert False, "regspec not found %s %s" % (regfile
, name
)