[sim] change applink for tohost/fromhost

riscv/applink.cc

@@ -53,6 +53,16 @@ void appserver_link_t::wait_for_start()
   while(wait_for_packet() != APP_CMD_START);
 }
 
+void appserver_link_t::wait_for_tohost()
+{
+  while(wait_for_packet() != APP_CMD_READ_CONTROL_REG);
+}
+
+void appserver_link_t::wait_for_fromhost()
+{
+  while(wait_for_packet() != APP_CMD_WRITE_CONTROL_REG);
+}
+
 void appserver_link_t::send_packet(packet* p)
 {
   while(1) try

riscv/sim.cc

@@ -27,12 +27,12 @@ void sim_t::set_tohost(reg_t val)
 {
   fromhost = 0;
   tohost = val;
+  applink->wait_for_tohost();
 }
 
 reg_t sim_t::get_fromhost()
 {
-  while(fromhost == 0)
-    applink->wait_for_packet();
+  applink->wait_for_fromhost();
   return fromhost;
 }