From 545e31c6f94508bc6f804a7e202a221d1867e035 Mon Sep 17 00:00:00 2001
From: Tom Barthe <tom.barthe@ens-paris-saclay.fr>
Date: Mon, 18 Jan 2021 03:47:58 +0100
Subject: [PATCH] Change the run_timers execution frequency

We now use the GCD of all the async timers.
---
 compiler/obc/c/async_avr.ml      | 33 +++++++++++++++++++++++---------
 compiler/obc/c/async_backend.mli |  2 +-
 compiler/obc/c/cmain.ml          |  5 ++++-
 lib/c/avr.c                      |  6 ++++--
 lib/c/avr.h                      |  2 +-
 5 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/compiler/obc/c/async_avr.ml b/compiler/obc/c/async_avr.ml
index 96b43fa..2566d4c 100644
--- a/compiler/obc/c/async_avr.ml
+++ b/compiler/obc/c/async_avr.ml
@@ -49,6 +49,8 @@ struct
 
   let fold_lcm l = List.fold_left lcm (List.hd l) (List.tl l)
 
+  let fold_gcd l = List.fold_left gcd (List.hd l) (List.tl l)
+
   let ms_of_ack = function
     | Timer_ms ms -> ms
 
@@ -58,34 +60,37 @@ struct
     let incr = Cbop ("+", Cvar name, one_const) in
     Caffect (CLvar name, Cbop ("%", incr, modulo_const))
 
-  let call_step_async tick_var (od, ack) =
+  let call_step_async tick_var base (od, ack) =
     let step = (cname_of_qn od.o_class) ^ "_async_step" in
     let global = async_global_var_name od in
     let call = Csexpr (Cfun_call (step, [Caddrof (Cvar global)])) in
     let zero = Cconst (Ccint 0) in
-    let timer = Cconst (Ccint (ms_of_ack ack)) in
+    let timer = Cconst (Ccint (ms_of_ack ack / base)) in
     let cond = Cbop ("==", Cbop ("%", tick_var, timer), zero) in
     Cif (cond, [call], [])
 
-  let decls_and_defs objs =
-    let trans = List.map
+  let translate_objs objs =
+    List.map
       (fun od ->
         let ack = Option.get od.o_ack in
         (od, translate_ack ack))
       objs
-    in
+
+  let decls_and_defs objs =
+    let trans = translate_objs objs in
     let timers = List.map
-      (fun (_, ack) -> match ack with Timer_ms ms -> ms)
+      (fun (_, ack) -> ms_of_ack ack)
       trans
     in
     let body = match timers with
       | [] -> []
       | _ ->
+         let gcd_timer = fold_gcd timers in
          let lcm_timer = fold_lcm timers in
          let steps =
-           List.map (call_step_async (Cvar "tick")) trans
+           List.map (call_step_async (Cvar "tick") gcd_timer) trans
          in
-         let incr = incr_mod "tick" lcm_timer in
+         let incr = incr_mod "tick" (lcm_timer / gcd_timer) in
          steps @ [incr]
     in
     (* run_timers is declared in avr.h (because of the ISR macro which
@@ -105,6 +110,16 @@ struct
     ] in
     [], defs
 
-  let main_init = [Csexpr (Cfun_call ("init_timer1", []))]
+  let main_init objs =
+    let trans = translate_objs objs in
+    let timers = List.map
+      (fun (_, ack) -> ms_of_ack ack)
+      trans
+    in
+    match timers with
+    | [] -> []
+    | _ ->
+      let value = fold_gcd timers in
+      [Csexpr (Cfun_call ("init_timer1", [Cconst (Ccint value)]))]
 
 end
diff --git a/compiler/obc/c/async_backend.mli b/compiler/obc/c/async_backend.mli
index ed322b7..6107b02 100644
--- a/compiler/obc/c/async_backend.mli
+++ b/compiler/obc/c/async_backend.mli
@@ -7,5 +7,5 @@ sig
   val gen_copy_func_out : class_def -> cdef
   val includes : string list
   val decls_and_defs : obj_dec list -> cdecl list * cdef list
-  val main_init : cstm list
+  val main_init : obj_dec list -> cstm list
 end
diff --git a/compiler/obc/c/cmain.ml b/compiler/obc/c/cmain.ml
index 7780abb..a01aeab 100644
--- a/compiler/obc/c/cmain.ml
+++ b/compiler/obc/c/cmain.ml
@@ -418,7 +418,10 @@ let mk_main name p =
        * could be triggered while the initial reset of the async nodes is
        * not yet terminated.
        *)
-      let res_l = res_l @ AvrBackend.main_init in
+      let async_objs = List.flatten
+        (List.map filter_async_objs classes)
+      in
+      let res_l = res_l @ AvrBackend.main_init async_objs in
 
       [("_main.c", Csource (defs @ [main_skel var_l res_l step_l]));
        ("_main.h", Cheader ([name], []))];
diff --git a/lib/c/avr.c b/lib/c/avr.c
index 7085fd0..513a6a6 100644
--- a/lib/c/avr.c
+++ b/lib/c/avr.c
@@ -30,6 +30,7 @@
 #include <util/atomic.h>
 #include <avr/interrupt.h>
 #include <avr/io.h>
+#include <assert.h>
 #include "avr.h"
 
 ISR(TIMER1_COMPA_vect) {
@@ -42,9 +43,10 @@ static inline void set_ocr1a(uint16_t value) {
 }
 
 /* Source: https://adnbr.co.uk/articles/counting-milliseconds */
-void init_timer1() {
+void init_timer1(unsigned int ms) {
+  assert(ms < 1000);
   TCCR1B |= _BV(WGM12) | _BV(CS11);
-  set_ocr1a((F_CPU / 1000) / 8);
+  set_ocr1a(((ms * F_CPU) / 1000) / 8);
   TIMSK1 |= _BV(OCIE1A);
   sei();
 }
diff --git a/lib/c/avr.h b/lib/c/avr.h
index 573f4d0..5b3027d 100644
--- a/lib/c/avr.h
+++ b/lib/c/avr.h
@@ -39,7 +39,7 @@
 
 void run_timers();
 
-void init_timer1();
+void init_timer1(unsigned int ms);
 
 void atomic_memcpy(void *dest, const void *src, size_t size);