Complète l'implémentation des syscalls

- Suppression provisoire de `input_string`
- Écriture de `print_string`

simulator/interpreter.ml

@@ -60,6 +60,7 @@ module Env = struct
       | n -> wrong_size n
 
   let ram env = env.ram
+  let rom env = env.rom
 end
 
 
@@ -184,6 +185,7 @@ let interp asm_file n script_mode input_c output_c p =
       )
       p.p_outputs;
     (* Handling system calls *)
-    let return_code = Ram.bits_of_int 32 @@ Syscall.syscall (Env.ram env) in
-    Env.write_on_ram 32 env [|true;true;false;false|] return_code
+    let return_code = Syscall.syscall (Env.ram env) (Env.rom env) in
+    let return_code_bin = Ram.bits_of_int 32 return_code in
+    Env.write_on_ram 32 env [|true;true;false;false|] return_code_bin
   done

simulator/syscall.ml

+(** Prints an integer on stdout and returns 0 *)
 let sys_print_int a0 =
-  Format.printf "\n\n ===> %d <== \n\n@?" a0;
+  Format.printf "%d@?" a0;
   0
 
-let sys_print_str _ = assert false
-
+(** Reads an integer from stdin and returns it *)
 let sys_input_int () = Scanf.scanf "%d " (fun x -> x)
 
-let sys_input_str _ _ = assert false
+(** Prints the string starting at start_addr in RAM on stdout.
+    The string must end with \000. *)
+let sys_print_str rom start_addr =
+  let addr = ref start_addr in
+  let current_char = ref 0 in
+  let read_char () =
+    let c = Ram.int_of_bits @@ Ram.get_byte rom !addr in
+    current_char := c;
+    incr addr in    
+  while (read_char () ; !current_char <> 0) do
+    print_char (char_of_int !current_char)
+  done;
+  0
 
+(** Stops the simulator execution, maybe a little bit violent but… It will do
+    the trick. *)
 let sys_exit () = exit 0
 
-let syscall ram =
+(** The switch for syscalls:
+    - The values of $a0, $a1, $v0 are read from the RAM
+    - The syscall is executed
+    - The return value is written at the right place in RAM
+*)
+let syscall ram rom =
   let a0 = Ram.int_of_bits @@ Ram.get_word ram 4 in
   let a1 = Ram.int_of_bits @@ Ram.get_word ram 8 in
   let v0 = Ram.int_of_bits @@ Ram.get_byte ram 1 in
   Printf.printf "SYSCALL: $v0=%d $a0=%d $a1=%d\n" v0 a0 a1;
   match v0 with
-    | 0 -> 0
+    | 0 -> 0 (* a dummy syscall *)
     | 1 -> sys_print_int a0
-    | 4 -> sys_print_str a0
+    | 4 -> sys_print_str rom a0
     | 5 -> sys_input_int ()
-    | 8 -> sys_input_str a0 a1
     | 10 -> sys_exit ()
-    | _ -> assert false
+    | n -> failwith @@
+        Printf.sprintf "Invalid syscall code: %d" n