From 755fd71c213ed77e9ac2a01bfdde7ae675985d3e Mon Sep 17 00:00:00 2001
From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 8 Jun 2020 23:52:54 +0100
Subject: [PATCH] add traptype and trapaddr to PowerDecoder2.  idea is to
 actually *change* the instruction depending on conditions detected by the
 decoder

---
 src/soc/decoder/power_decoder2.py | 21 +++++++++++++++++++++
 src/soc/fu/trap/main_stage.py     |  6 +++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/soc/decoder/power_decoder2.py b/src/soc/decoder/power_decoder2.py
index 27cd5fa3..5aca9d85 100644
--- a/src/soc/decoder/power_decoder2.py
+++ b/src/soc/decoder/power_decoder2.py
@@ -18,6 +18,13 @@ from soc.decoder.power_enums import (InternalOp, CryIn, Function,
 
 from soc.regfile.regfiles import FastRegs
 
+# see traptype (and trap main_stage.py)
+
+TT_FP = 1<<0
+TT_PRIV = 1<<1
+TT_TRAP = 1<<2
+TT_ADDR = 1<<3
+
 
 def instr_is_privileged(m, op, insn):
     """determines if the instruction is privileged or not
@@ -532,6 +539,8 @@ class Decode2ToExecute1Type(RecordObject):
         self.byte_reverse  = Signal(reset_less=True)
         self.sign_extend  = Signal(reset_less=True)# do we need this?
         self.update  = Signal(reset_less=True) # LD/ST is "update" variant
+        self.traptype  = Signal(4, reset_less=True) # see trap main_stage.py
+        self.trapaddr  = Signal(13, reset_less=True)
 
 
 class PowerDecode2(Elaboratable):
@@ -647,7 +656,19 @@ class PowerDecode2(Elaboratable):
         comb += e.input_cr.eq(op.cr_in)   # condition reg comes in
         comb += e.output_cr.eq(op.cr_out) # condition reg goes in
 
+        with m.If(op.internal_op == InternalOp.OP_TRAP):
+            comb += e.traptype.eq(TT_TRAP) # request trap interrupt
+            comb += e.trapaddr.eq(0x70)    # addr=0x700 (strip first nibble)
+
+        return m
 
+        # privileged instruction
+        with m.If(instr_is_privileged(m, op.internal_op, e.insn) &
+                  msr[MSR_PR]):
+            # privileged instruction trap
+            comb += op.internal_op.eq(InternalOp.OP_TRAP)
+            comb += e.traptype.eq(TT_PRIV) # request privileged instruction
+            comb += e.trapaddr.eq(0x70)    # addr=0x700 (strip first nibble)
         return m
 
     def regspecmap(self, regfile, regname):
diff --git a/src/soc/fu/trap/main_stage.py b/src/soc/fu/trap/main_stage.py
index 17a9da84..fe018d8f 100644
--- a/src/soc/fu/trap/main_stage.py
+++ b/src/soc/fu/trap/main_stage.py
@@ -33,11 +33,15 @@ MSR_LE  = (63 - 63)    # Little Endian
 
 # Listed in V3.0B Book III 7.5.9 "Program Interrupt"
 
-PI_PRIV = (63 - 43)    # 1 if FP exception
+# note that these correspond to trap_input_record.traptype bits 0,1,2,3
+# (TODO: add more?)
+
+PI_FP   = (63 - 43)    # 1 if FP exception
 PI_PRIV = (63 - 45)    # 1 if privileged interrupt
 PI_TRAP = (63 - 46)    # 1 if exception is "trap" type
 PI_ADR  = (63 - 47)    # 0 if SRR0 = address of instruction causing exception
 
+
 def msr_copy(msr_o, msr_i, zero_me=True):
     """
     -- ISA says this:
-- 
2.30.2