LongitudinalMpc: use DT_MDL (#32532)

bad magic number
old-commit-hash: 6ecb710305

selfdrive/controls/lib/longitudinal_mpc_lib/long_mpc.py

@@ -4,6 +4,7 @@ import time
 import numpy as np
 from cereal import log
 from openpilot.common.numpy_fast import clip
+from openpilot.common.realtime import DT_MDL
 from openpilot.common.swaglog import cloudlog
 # WARNING: imports outside of constants will not trigger a rebuild
 from openpilot.selfdrive.modeld.constants import index_function
@@ -220,8 +221,9 @@ def gen_long_ocp():
 
 
 class LongitudinalMpc:
-  def __init__(self, mode='acc'):
+  def __init__(self, mode='acc', dt=DT_MDL):
     self.mode = mode
+    self.dt = dt
     self.solver = AcadosOcpSolverCython(MODEL_NAME, ACADOS_SOLVER_TYPE, N)
     self.reset()
     self.source = SOURCES[2]
@@ -440,7 +442,7 @@ class LongitudinalMpc:
     self.a_solution = self.x_sol[:,2]
     self.j_solution = self.u_sol[:,0]
 
-    self.prev_a = np.interp(T_IDXS + 0.05, T_IDXS, self.a_solution)
+    self.prev_a = np.interp(T_IDXS + self.dt, T_IDXS, self.a_solution)
 
     t = time.monotonic()
     if self.solution_status != 0:

selfdrive/controls/lib/longitudinal_planner.py

@@ -47,7 +47,7 @@ def limit_accel_in_turns(v_ego, angle_steers, a_target, CP):
 class LongitudinalPlanner:
   def __init__(self, CP, init_v=0.0, init_a=0.0, dt=DT_MDL):
     self.CP = CP
-    self.mpc = LongitudinalMpc()
+    self.mpc = LongitudinalMpc(dt=dt)
     self.fcw = False
     self.dt = dt