Stop yields when yield is disabled.

src/machine-state.h

@@ -183,10 +183,23 @@ struct machine_state {
         return brk;
     }
 
+    /// \brief Decide if brk should be set due to yield.
+    bool brk_from_iflags_Y(void) const {
+        if (iflags.Y) {
+            // uint64_t dev = HTIF_DEV_FIELD(htif.tohost);
+            uint64_t dev = htif.tohost >> 56;
+            // uint64_t cmd = HTIF_CMD_FIELD(htif.tohost)
+            uint64_t cmd = htif.tohost << 8 >> 48;
+            // brk |= (dev == HTIF_DEVICE_YIELD && (htif.iyield >> cmd));
+            return (dev == 2 && ((htif.iyield >> cmd) & 1));
+        }
+        return false;
+    }
+
     /// \brief Checks that false brk is consistent with rest of state
     void assert_no_brk(void) const {
         assert((mie & mip) == 0);
-        assert(!iflags.Y);
+        assert(!brk_from_iflags_Y());
         assert(!iflags.H);
     }
 
@@ -202,7 +215,7 @@ struct machine_state {
 
     /// \brief Updates the brk flag from changes in the iflags_Y flag.
     void or_brk_with_iflags_Y(void) {
-        brk |= iflags.Y;
+        brk |= brk_from_iflags_Y();
     }
 
     /// \brief Rebuild brk from all.

src/machine.cpp

@@ -169,6 +169,10 @@ void machine::interact(void) {
     m_h.interact();
 }
 
+bool machine::should_yield(void) const {
+    return m_s.brk_from_iflags_Y();
+}
+
 machine::machine(const machine_config &c):
     m_s{},
     m_t{},
@@ -1200,7 +1204,7 @@ access_log machine::step(const access_log::type &log_type, bool one_based) {
         hash_type root_hash_after;
         update_merkle_tree();
         get_root_hash(root_hash_after);
-        verify_state_transition(root_hash_before, *a.get_log(), 
+        verify_state_transition(root_hash_before, *a.get_log(),
             root_hash_after, one_based);
     } else {
         verify_access_log(*a.get_log(), one_based);
@@ -1249,7 +1253,7 @@ void machine::run(uint64_t mcycle_end) {
         }
 
         // If we yielded, we are done
-        if (read_iflags_Y()) {
+        if (should_yield()) {
             return;
         }
     }

src/machine.h

@@ -77,6 +77,9 @@ class machine final {
     ///  instruction. Another example is when the machine halts.
     void run_inner_loop(uint64_t mcycle_end);
 
+    /// \brief Decides if machine should yield
+    bool should_yield(void) const;
+
 public:
 
     /// \brief Type of hash