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Implement misa CSR #743

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merged 3 commits into from
Nov 12, 2024
Merged

Implement misa CSR #743

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8c0289f
Implement misa CSR
piotro888 Oct 23, 2024
437af45
Remove width check
piotro888 Nov 10, 2024
bad17e7
Merge branch 'master' into piotro/misa
tilk Nov 12, 2024
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37 changes: 35 additions & 2 deletions coreblocks/priv/csr/csr_instances.py
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Original file line number Diff line number Diff line change
Expand Up @@ -84,6 +84,10 @@ def __init__(self, gen_params: GenParams):

self.mtval = CSRRegister(CSRAddress.MTVAL, gen_params)

self.misa = CSRRegister(
CSRAddress.MISA, gen_params, init=self._misa_value(gen_params), ro_bits=(1 << gen_params.isa.xlen) - 1
)

self.priv_mode = CSRRegister(
None,
gen_params,
Expand All @@ -94,7 +98,7 @@ def __init__(self, gen_params: GenParams):
self.priv_mode_public = AliasedCSR(CSRAddress.COREBLOCKS_TEST_PRIV_MODE, gen_params)
self.priv_mode_public.add_field(0, self.priv_mode)

self.mstatus_fields_implementation(gen_params, self.mstatus, self.mstatush)
self._mstatus_fields_implementation(gen_params, self.mstatus, self.mstatush)

def elaborate(self, platform):
m = Module()
Expand All @@ -105,7 +109,7 @@ def elaborate(self, platform):

return m

def mstatus_fields_implementation(self, gen_params: GenParams, mstatus: AliasedCSR, mstatush: AliasedCSR):
def _mstatus_fields_implementation(self, gen_params: GenParams, mstatus: AliasedCSR, mstatush: AliasedCSR):
def filter_legal_priv_mode(m: TModule, v: Value):
legal = Signal(1)
with m.Switch(v):
Expand Down Expand Up @@ -179,6 +183,35 @@ def filter_legal_priv_mode(m: TModule, v: Value):
Extension.V in gen_params.isa.extensions or Extension.F in gen_params.isa.extensions,
)

def _misa_value(self, gen_params):
misa_value = 0

misa_extension_bits = {
0: Extension.A,
1: Extension.B,
2: Extension.C,
3: Extension.D,
4: Extension.E,
5: Extension.F,
8: Extension.I,
12: Extension.M,
16: Extension.Q,
21: Extension.V,
}

for bit, extension in misa_extension_bits.items():
if extension in gen_params.isa.extensions:
misa_value |= 1 << bit

if gen_params.user_mode:
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Why user_mode is handled separately? From ISA point of view it is "U" extension.

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It is treated as extension only in misa. It is not present in isa strings, not defined as extension in spec, doesn't define instructions and only changes CSR behaviour (and can't be determined from FU config, so needs config flag anyway)
I think it is better to not add it to isa.extensions

misa_value |= 1 << 20
# 7 - Hypervisor, 18 - Supervisor, 23 - Custom Extensions

xml_field_mapping = {32: XlenEncoding.W32, 64: XlenEncoding.W64, 128: XlenEncoding.W128}
misa_value |= xml_field_mapping[gen_params.isa.xlen] << (gen_params.isa.xlen - 2)

return misa_value


class GenericCSRRegisters(Elaboratable):
def __init__(self, gen_params: GenParams):
Expand Down