From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Wed, 17 Oct 2018 00:58:15 +0000 (+0100)
Subject: minor alteration to CSRRWI SETVL / SETMVL to offset immediate by 1
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=a161d1b9d4db96d1b6ce2fec7b66325d9144a08b;p=riscv-isa-sim.git

minor alteration to CSRRWI SETVL / SETMVL to offset immediate by 1

allows CSRRWI to make maximum use of only 5-bit immediate
---

diff --git a/riscv/insns/csrrwi.h b/riscv/insns/csrrwi.h
index 8a253ee..69c5472 100644
--- a/riscv/insns/csrrwi.h
+++ b/riscv/insns/csrrwi.h
@@ -6,10 +6,12 @@ reg_t old = 0; // stop compiler bitchin
 if (csr != CSR_USVVL && csr != CSR_USVMVL)
 {
     old = p->get_csr(csr);
+    p->set_csr(csr, insn.rs1());
 }
-p->set_csr(csr, insn.rs1());
+else
 if (csr == CSR_USVVL || csr == CSR_USVMVL)
 {
+    p->set_csr(csr, insn.rs1()+1); // must add one here
     old = p->get_csr(csr);
 }
 #else
diff --git a/riscv/processor.cc b/riscv/processor.cc
index 5b73dcc..b95c030 100644
--- a/riscv/processor.cc
+++ b/riscv/processor.cc
@@ -344,18 +344,20 @@ void processor_t::set_csr(int which, reg_t val)
   {
 #ifdef SPIKE_SIMPLEV
     case CSR_USVMVL:
-      state.mvl = std::min(val+1, (uint64_t)64); // limited to XLEN width
+      state.mvl = std::min(val, (uint64_t)64); // limited to XLEN width
+      // TODO XXX throw exception if val == 0
       fprintf(stderr, "set MVL %lx\n", state.mvl);
       break;
     case CSR_USVSTATE:
       // bits 0-5: mvl - 6-11: vl - 12-17: srcoffs - 18-23: destoffs
-      set_csr(CSR_USVMVL, get_field(val, 0x1f));
-      set_csr(CSR_USVVL , get_field(val, 0x1f<<6));
-      state.srcoffs = std::min(get_field(val, 0x1f<<12), state.vl-1);
+      set_csr(CSR_USVMVL, get_field(val, 0x1f   )+1);
+      set_csr(CSR_USVVL , get_field(val, 0x1f<<6)+1);
+      state.srcoffs  = std::min(get_field(val, 0x1f<<12), state.vl-1);
       state.destoffs = std::min(get_field(val, 0x1f<<18), state.vl-1);
       break;
     case CSR_USVVL:
-      state.vl = std::min(state.mvl, val+1);
+      state.vl = std::min(state.mvl, val);
+      // TODO XXX throw exception if val == 0
       fprintf(stderr, "set VL %lx\n", state.vl);
       break;
     case CSR_SVREGCFG0: