legalize menvcfg.CBIE

The value 2 of menvcfg.CBIE is reserved. This commit legalizes it to 0
by adding a specialized class envcfg_csr_t.

Reference: https://github.com/riscv/riscv-CMOs/issues/65

1 files changed, 13 insertions, 0 deletions

diff --git a/riscv/csrs.cc b/riscv/csrs.cc
index 7ea07d1..a895b6c 100644
--- a/riscv/csrs.cc
+++ b/riscv/csrs.cc
@@ -901,6 +901,19 @@ bool masked_csr_t::unlogged_write(const reg_t val) noexcept {
   return basic_csr_t::unlogged_write((read() & ~mask) | (val & mask));
 }
 
+envcfg_csr_t::envcfg_csr_t(processor_t* const proc, const reg_t addr, const reg_t mask,
+                             const reg_t init):
+  masked_csr_t(proc, addr, mask, init) {
+  // In unlogged_write() we WARLize this field for all three of [msh]envcfg
+  assert(MENVCFG_CBIE == SENVCFG_CBIE && MENVCFG_CBIE == HENVCFG_CBIE);
+}
+
+bool envcfg_csr_t::unlogged_write(const reg_t val) noexcept {
+  const reg_t cbie_reserved = 2; // Reserved value of xenvcfg.CBIE
+  const reg_t adjusted_val = get_field(val, MENVCFG_CBIE) != cbie_reserved ? val : set_field(val, MENVCFG_CBIE, 0);
+  return masked_csr_t::unlogged_write(adjusted_val);
+}
+
 // implement class henvcfg_csr_t
 henvcfg_csr_t::henvcfg_csr_t(processor_t* const proc, const reg_t addr, const reg_t mask, const reg_t init, csr_t_p menvcfg):
   masked_csr_t(proc, addr, mask, init),