--- /dev/null
+""" TLB Module
+
+ The expected form of the data is:
+ * Item (Bits)
+ * Tag (N - 79) / ASID (78 - 64) / PTE (63 - 0)
+"""
+
+from nmigen import Memory, Module, Signal, Cat
+from nmigen.cli import main
+
+from PermissionValidator import PermissionValidator
+from Cam import Cam
+
+class TLB():
+ def __init__(self, asid_size, vma_size, pte_size, L1_size):
+ """ Arguments
+ * asid_size: Address Space IDentifier (ASID) typically 15 bits
+ * vma_size: Virtual Memory Address (VMA) typically 36 bits
+ * pte_size: Page Table Entry (PTE) typically 64 bits
+
+ Notes:
+ These arguments should represent the largest possible size
+ defined by the MODE settings. See
+ Volume II: RISC-V Privileged Architectures V1.10 Page 57
+ """
+
+ # Internal
+ self.state = 0
+ # L1 Cache Modules
+ L1_size = 8 # XXX overridden incoming argument?
+ self.cam_L1 = Cam(vma_size, L1_size)
+ self.mem_L1 = Memory(asid_size + pte_size, L1_size)
+
+ # Permission Validator
+ self.perm_validator = PermissionValidator(asid_size, pte_size)
+
+ # Inputs
+ self.supermode = Signal(1) # Supervisor Mode
+ self.super_access = Signal(1) # Supervisor Access
+ self.command = Signal(2) # 00=None, 01=Search, 10=Write L1, 11=Write L2
+ self.xwr = Signal(3) # Execute, Write, Read
+ self.mode = Signal(4) # 4 bits for access to Sv48 on Rv64
+ self.address_L1 = Signal(max=L1_size)
+ self.asid = Signal(asid_size) # Address Space IDentifier (ASID)
+ self.vma = Signal(vma_size) # Virtual Memory Address (VMA)
+ self.pte_in = Signal(pte_size) # To be saved Page Table Entry (PTE)
+
+ # Outputs
+ self.hit = Signal(1) # Denotes if the VMA had a mapped PTE
+ self.perm_valid = Signal(1) # Denotes if the permissions are correct
+ self.pte_out = Signal(pte_size) # PTE that was mapped to by the VMA
+
+ def search(self, m, read_L1, write_L1):
+ """ searches the TLB
+ """
+ m.d.comb += [
+ write_L1.en.eq(0),
+ self.cam_L1.write_enable.eq(0),
+ self.cam_L1.data_in.eq(self.vma)
+ ]
+ # Match found in L1 CAM
+ match_found = Signal(reset_less=True)
+ m.d.comb += match_found.eq(self.cam_L1.single_match
+ | self.cam_L1.multiple_match)
+ with m.If(match_found):
+ # Memory shortcut variables
+ mem_address = self.cam_L1.match_address
+ # Memory Logic
+ m.d.comb += read_L1.addr.eq(mem_address)
+ # Permission Validator Logic
+ m.d.comb += [
+ self.hit.eq(1),
+ # Set permission validator data to the correct
+ # register file data according to CAM match
+ # address
+ self.perm_validator.data.eq(read_L1.data),
+ # Execute, Read, Write
+ self.perm_validator.xwr.eq(self.xwr),
+ # Supervisor Mode
+ self.perm_validator.super_mode.eq(self.supermode),
+ # Supverisor Access
+ self.perm_validator.super_access.eq(self.super_access),
+ # Address Space IDentifier (ASID)
+ self.perm_validator.asid.eq(self.asid),
+ # Output result of permission validation
+ self.perm_valid.eq(self.perm_validator.valid)
+ ]
+ # Only output PTE if permissions are valid
+ with m.If(self.perm_validator.valid):
+ # XXX TODO - dummy for now
+ reg_data = Signal.like(self.pte_out)
+ m.d.comb += [
+ self.pte_out.eq(reg_data)
+ ]
+ with m.Else():
+ m.d.comb += [
+ self.pte_out.eq(0)
+ ]
+ # Miss Logic
+ with m.Else():
+ m.d.comb += [
+ self.hit.eq(0),
+ self.perm_valid.eq(0),
+ self.pte_out.eq(0)
+ ]
+
+ def write_l1(self, m, read_L1, write_L1):
+ """ writes to the L1 cache
+ """
+ # Memory_L1 Logic
+ m.d.comb += [
+ write_L1.en.eq(1),
+ write_L1.addr.eq(self.address_L1),
+ # The Cat places arguments from LSB -> MSB
+ write_L1.data.eq(Cat(self.pte_in, self.asid))
+ ]
+ # CAM_L1 Logic
+ m.d.comb += [
+ self.cam_L1.write_enable.eq(1),
+ self.cam_L1.data_in.eq(self.vma),
+ ]
+
+ def elaborate(self, platform):
+ m = Module()
+ # Add submodules
+ # Submodules for L1 Cache
+ m.d.submodules.cam_L1 = self.cam_L1
+ m.d.sumbmodules.read_L1 = read_L1 = self.mem_L1.read_port()
+ m.d.sumbmodules.read_L1 = write_L1 = self.mem_L1.write_port()
+ # Permission Validator Submodule
+ m.d.submodules.perm_valididator = self.perm_validator
+
+ # When MODE specifies translation
+ # TODO add in different bit length handling ie prefix 0s
+ tlb_enable = Signal(reset_less=True)
+ m.d.comb += tlb_enable.eq(self.mode != 0)
+
+ with m.If(tlb_enable):
+ m.d.comb += [
+ self.cam_L1.enable.eq(1)
+ ]
+ with m.Switch(self.command):
+ # Search
+ with m.Case("01"):
+ self.search(m, read_L1, write_L1)
+
+ # Write L1
+ # Expected that the miss will be handled in software
+ with m.Case("10"):
+ self.write_l1(m, read_L1, write_L1)
+
+ # TODO
+ #with m.Case("11"):
+
+ # When disabled
+ with m.Else():
+ m.d.comb += [
+ self.cam_L1.enable.eq(0),
+ # XXX TODO - self.reg_file.enable.eq(0),
+ self.hit.eq(0),
+ self.perm_valid.eq(0), # XXX TODO, check this
+ self.pte_out.eq(0)
+ ]
+ return m
+
+
+if __name__ == '__main__':
+ tlb = TLB(15, 36, 64, 4)
+ main(tlb, ports=[ tlb.supermode, tlb.super_access, tlb.command,
+ tlb.xwr, tlb.mode, tlb.address_L1, tlb.asid,
+ tlb.vma, tlb.pte_in,
+ tlb.hit, tlb.perm_valid, tlb.pte_out,
+ ] + tlb.cam_L1.ports())
projects / soc.git / blobdiff