From e103247b196ca128bfbf4b4c6c0d68e63e64b98b Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 26 Nov 2018 02:54:25 +0000
Subject: [PATCH] add csr_is_valid

---
 cpu.py | 166 ++++++++++++---------------------------------------------
 1 file changed, 34 insertions(+), 132 deletions(-)

diff --git a/cpu.py b/cpu.py
index 8baa0be..c8dafde 100644
--- a/cpu.py
+++ b/cpu.py
@@ -328,72 +328,38 @@ class CPU(Module):
         s.append(i)
         return s
 
-    """
-    function get_csr_op_is_valid(input [11:0] csr_number, input csr_reads, input csr_writes);
-    begin
-        case(csr_number)
-        `csr_ustatus,
-        `csr_fflags,
-        `csr_frm,
-        `csr_fcsr,
-        `csr_uie,
-        `csr_utvec,
-        `csr_uscratch,
-        `csr_uepc,
-        `csr_ucause,
-        `csr_utval,
-        `csr_uip,
-        `csr_sstatus,
-        `csr_sedeleg,
-        `csr_sideleg,
-        `csr_sie,
-        `csr_stvec,
-        `csr_scounteren,
-        `csr_sscratch,
-        `csr_sepc,
-        `csr_scause,
-        `csr_stval,
-        `csr_sip,
-        `csr_satp,
-        `csr_medeleg,
-        `csr_mideleg,
-        `csr_dcsr,
-        `csr_dpc,
-        `csr_dscratch:
-            get_csr_op_is_valid = 0;
-        `csr_cycle,
-        `csr_time,
-        `csr_instret,
-        `csr_cycleh,
-        `csr_timeh,
-        `csr_instreth,
-        `csr_mvendorid,
-        `csr_marchid,
-        `csr_mimpid,
-        `csr_mhartid:
-            get_csr_op_is_valid = ~csr_writes;
-        `csr_misa,
-        `csr_mstatus,
-        `csr_mie,
-        `csr_mtvec,
-        `csr_mscratch,
-        `csr_mepc,
-        `csr_mcause,
-        `csr_mip:
-            get_csr_op_is_valid = 1;
-        `csr_mcounteren,
-        `csr_mtval,
-        `csr_mcycle,
-        `csr_minstret,
-        `csr_mcycleh,
-        `csr_minstreth:
-            // TODO: CSRs not implemented yet
-            get_csr_op_is_valid = 0;
-        endcase
-    end
-    endfunction
-
-    """
+    def get_csr_op_is_valid(self, csr_op_is_valid, csr_number,
+                                  csr_reads, csr_writes):
+        """ determines if a CSR is valid
+        """
+        c = {}
+        # invalid csrs
+        for f in [csr_ustatus, csr_fflags, csr_frm, csr_fcsr,
+                  csr_uie, csr_utvec, csr_uscratch, csr_uepc,
+                  csr_ucause, csr_utval, csr_uip, csr_sstatus,
+                  csr_sedeleg, csr_sideleg, csr_sie, csr_stvec,
+                  csr_scounteren, csr_sscratch, csr_sepc, csr_scause,
+                  csr_stval, csr_sip, csr_satp, csr_medeleg,
+                  csr_mideleg, csr_dcsr, csr_dpc, csr_dscratch]:
+            c[f] = csr_op_is_valid.eq(0)
+
+        # not-writeable -> ok
+        for f in [csr_cycle, csr_time, csr_instret, csr_cycleh,
+                  csr_timeh, csr_instreth, csr_mvendorid, csr_marchid,
+                  csr_mimpid, csr_mhartid]:
+            c[f] = csr_op_is_valid.eq(~csr_writes)
+
+        # valid csrs
+        for f in [csr_misa, csr_mstatus, csr_mie, csr_mtvec,
+                  csr_mscratch, csr_mepc, csr_mcause, csr_mip]:
+            c[f] = csr_op_is_valid.eq(1)
+
+        # not implemented / default
+        for f in [csr_mcounteren, csr_mtval, csr_mcycle, csr_minstret,
+                  csr_mcycleh, csr_minstreth, "default"]:
+            c[f] = csr_op_is_valid.eq(0)
+
+        return Case(csr_number, c)
 
     def __init__(self):
         self.clk = ClockSignal()
@@ -653,6 +619,8 @@ class CPU(Module):
         self.comb += csr_reads.eq(dc.funct3[1] | (dc.rd != 0))
         self.comb += csr_writes.eq(~dc.funct3[1] | (dc.rs1 != 0))
 
+        self.comb += self.get_csr_op_is_valid(csr_op_is_valid, csr_number,
+                                              csr_reads, csr_writes)
 
 if __name__ == "__main__":
     example = CPU()
@@ -669,72 +637,6 @@ if __name__ == "__main__":
 
 """
 
-    function get_csr_op_is_valid(input [11:0] csr_number, input csr_reads, input csr_writes);
-    begin
-        case(csr_number)
-        `csr_ustatus,
-        `csr_fflags,
-        `csr_frm,
-        `csr_fcsr,
-        `csr_uie,
-        `csr_utvec,
-        `csr_uscratch,
-        `csr_uepc,
-        `csr_ucause,
-        `csr_utval,
-        `csr_uip,
-        `csr_sstatus,
-        `csr_sedeleg,
-        `csr_sideleg,
-        `csr_sie,
-        `csr_stvec,
-        `csr_scounteren,
-        `csr_sscratch,
-        `csr_sepc,
-        `csr_scause,
-        `csr_stval,
-        `csr_sip,
-        `csr_satp,
-        `csr_medeleg,
-        `csr_mideleg,
-        `csr_dcsr,
-        `csr_dpc,
-        `csr_dscratch:
-            get_csr_op_is_valid = 0;
-        `csr_cycle,
-        `csr_time,
-        `csr_instret,
-        `csr_cycleh,
-        `csr_timeh,
-        `csr_instreth,
-        `csr_mvendorid,
-        `csr_marchid,
-        `csr_mimpid,
-        `csr_mhartid:
-            get_csr_op_is_valid = ~csr_writes;
-        `csr_misa,
-        `csr_mstatus,
-        `csr_mie,
-        `csr_mtvec,
-        `csr_mscratch,
-        `csr_mepc,
-        `csr_mcause,
-        `csr_mip:
-            get_csr_op_is_valid = 1;
-        `csr_mcounteren,
-        `csr_mtval,
-        `csr_mcycle,
-        `csr_minstret,
-        `csr_mcycleh,
-        `csr_minstreth:
-            // TODO: CSRs not implemented yet
-            get_csr_op_is_valid = 0;
-        endcase
-    end
-    endfunction
-
-    assign csr_op_is_valid = get_csr_op_is_valid(csr_number, csr_reads, csr_writes);
-
     wire [63:0] cycle_counter = 0; // TODO: implement cycle_counter
     wire [63:0] time_counter = 0; // TODO: implement time_counter
     wire [63:0] instret_counter = 0; // TODO: implement instret_counter
-- 
2.30.2