diff --git a/src/emc/kinematics/maxkins.c b/src/emc/kinematics/maxkins.c
index 773525b3566..d2623e0ad62 100644
--- a/src/emc/kinematics/maxkins.c
+++ b/src/emc/kinematics/maxkins.c
@@ -50,10 +50,6 @@ int kinematicsForward(const double *joints,
     // B correction
     const double zb = (pivot_length + joints[8] + tool_length) * cos(d2r(joints[4]));
     const double xb = (pivot_length + joints[8] + tool_length) * sin(d2r(joints[4]));
-        
-    // C correction
-    const double xyr = hypot(joints[0], joints[1]);
-    const double xytheta = atan2(joints[1], joints[0]) + d2r(joints[5]);
 
     // U correction
     const double zv = joints[6] * sin(d2r(joints[4]));
@@ -61,8 +57,18 @@ int kinematicsForward(const double *joints,
 
     // V correction is always in joint 1 only
 
-    pos->tran.x = xyr * cos(xytheta) - (con * xb) - xv;
-    pos->tran.y = xyr * sin(xytheta) - joints[7];
+    // B, U and V are all machine frame: the head hangs off the Z slide and
+    // does not turn with the C table, so they apply before the rotation into
+    // the workpiece frame rather than after it.
+    const double mx = joints[0] - (con * xb) - xv;
+    const double my = joints[1] - joints[7];
+
+    // C correction
+    const double xyr = hypot(mx, my);
+    const double xytheta = atan2(my, mx) + d2r(joints[5]);
+
+    pos->tran.x = xyr * cos(xytheta);
+    pos->tran.y = xyr * sin(xytheta);
     pos->tran.z = joints[2] - zb - (con * zv) + pivot_length + tool_length;
 
     pos->a = joints[3];
@@ -103,7 +109,7 @@ int kinematicsInverse(const EmcPose * pos,
 
     joints[0] = xyr * cos(xytheta) + (con * xb) + xv;
     joints[1] = xyr * sin(xytheta) + pos->v;
-    joints[2] = pos->tran.z + zb - (con * zv) - pivot_length - tool_length;
+    joints[2] = pos->tran.z + zb + (con * zv) - pivot_length - tool_length;
 
     joints[3] = pos->a;
     joints[4] = pos->b;
diff --git a/src/emc/kinematics/pumakins.c b/src/emc/kinematics/pumakins.c
index 98dc83aa4c5..049d384b424 100644
--- a/src/emc/kinematics/pumakins.c
+++ b/src/emc/kinematics/pumakins.c
@@ -29,6 +29,16 @@ struct haldata {
     hal_real_t a2, a3, d3, d4, d6;
 } *haldata = NULL;
 
+/* the difference of two angles, brought into (-pi, pi] so that a joint a
+   whole turn from the formula still matches it */
+static double angleDiff(double a, double b)
+{
+   double d = a - b;
+   while (d > PM_PI) { d -= 2*PM_PI; }
+   while (d <= -PM_PI) { d += 2*PM_PI; }
+   return d;
+}
+
 /* The flange orientation for a joint set: the ISO 9787 mechanical interface
    frame, whose z points out of the interface towards the work.  Shared by the
    forward kinematics and the tool frame so the two cannot drift apart. */
@@ -152,16 +162,16 @@ static int pumaKinematicsForward(const double * joint,
    *iflags = 0;
 
    /* Set shoulder-up flag if necessary */
-   if (fabs(joint[0]*PM_PI/180 - atan2(hom.tran.y, hom.tran.x) +
-       atan2(PUMA_D3, -sqrt(sumSq))) < FLAG_FUZZ)
+   if (fabs(angleDiff(joint[0]*PM_PI/180, atan2(hom.tran.y, hom.tran.x) -
+       atan2(PUMA_D3, -sqrt(sumSq)))) < FLAG_FUZZ)
    {
      *iflags |= PUMA_SHOULDER_RIGHT;
    }
 
    /* Set elbow down flag if necessary */
-   if (fabs(joint[2]*PM_PI/180 - atan2(PUMA_A3, PUMA_D4) +
+   if (fabs(angleDiff(joint[2]*PM_PI/180, atan2(PUMA_A3, PUMA_D4) -
        atan2(k, -sqrt(PUMA_A3 * PUMA_A3 +
-       PUMA_D4 * PUMA_D4 - k * k))) < FLAG_FUZZ)
+       PUMA_D4 * PUMA_D4 - k * k)))) < FLAG_FUZZ)
    {
       *iflags |= PUMA_ELBOW_DOWN;
    }
@@ -177,7 +187,7 @@ static int pumaKinematicsForward(const double * joint,
 
    /* if not singular set wrist flip flag if necessary */
    else{
-     if (! (fabs(joint[3]*PM_PI/180 - atan2(t1, t2)) < FLAG_FUZZ))
+     if (! (fabs(angleDiff(joint[3]*PM_PI/180, atan2(t1, t2))) < FLAG_FUZZ))
      {
        *iflags |= PUMA_WRIST_FLIP;
      }
diff --git a/src/emc/kinematics/scarakins.c b/src/emc/kinematics/scarakins.c
index 8db57eb7b0c..3b0e69ee7e4 100644
--- a/src/emc/kinematics/scarakins.c
+++ b/src/emc/kinematics/scarakins.c
@@ -96,8 +96,9 @@ int scaraKinematicsForward(const double * joint,
     z = D1 + D3 - joint[2] - D5;
     c = a3;
 
+    // the elbow flag: which sign the inverse gives the acos of joint 1
     *iflags = 0;
-    if (joint[1] < 90)
+    if (joint[1] < 0)
         *iflags = 1;
 
     world->tran.x = x;
diff --git a/src/emc/kinematics/three21kins.c b/src/emc/kinematics/three21kins.c
index a5a7b5dfa8f..2a3dfe08ee5 100644
--- a/src/emc/kinematics/three21kins.c
+++ b/src/emc/kinematics/three21kins.c
@@ -32,6 +32,16 @@ struct haldata {
     hal_real_t a1, a2, a3, d1, d2, d3, d4, d6;
 } *haldata = NULL;
 
+/* the difference of two angles, brought into (-pi, pi] so that a joint a
+   whole turn from the formula still matches it */
+static double angleDiff(double a, double b)
+{
+   double d = a - b;
+   while (d > PM_PI) { d -= 2*PM_PI; }
+   while (d <= -PM_PI) { d += 2*PM_PI; }
+   return d;
+}
+
 static int three21KinematicsForward(const double * joint,
                                     EmcPose * world,
                                     const KINEMATICS_FORWARD_FLAGS * fflags,
@@ -132,8 +142,8 @@ static int three21KinematicsForward(const double * joint,
    *iflags = 0;
 
    /* set shoulder flag */
-   if (fabs(joint[0]*PM_PI/180 - atan2(hom.tran.y, hom.tran.x) +
-       atan2(d23, -sqrt(sumSq))) < FLAG_FUZZ)
+   if (fabs(angleDiff(joint[0]*PM_PI/180, atan2(hom.tran.y, hom.tran.x) -
+       atan2(d23, -sqrt(sumSq)))) < FLAG_FUZZ)
    {
      *iflags |= THREE21_SHOULDER_RIGHT;
    }
@@ -143,8 +153,8 @@ static int three21KinematicsForward(const double * joint,
    if (discr < 0.0) {
        discr = 0.0;
    }
-   if (fabs(joint[2]*PM_PI/180 - atan2(a3, d4) +
-       atan2(k, -sqrt(discr))) < FLAG_FUZZ)
+   if (fabs(angleDiff(joint[2]*PM_PI/180, atan2(a3, d4) -
+       atan2(k, -sqrt(discr)))) < FLAG_FUZZ)
    {
       *iflags |= THREE21_ELBOW_DOWN;
    }
@@ -158,7 +168,7 @@ static int three21KinematicsForward(const double * joint,
    }
    else
    {
-     if (! (fabs(joint[3]*PM_PI/180 - atan2(t1, t2)) < FLAG_FUZZ))
+     if (! (fabs(angleDiff(joint[3]*PM_PI/180, atan2(t1, t2))) < FLAG_FUZZ))
      {
        *iflags |= THREE21_WRIST_FLIP;
      }
diff --git a/src/emc/kinematics/trtfuncs.c b/src/emc/kinematics/trtfuncs.c
index 31c9ff1a6de..0cb4b5eb7aa 100644
--- a/src/emc/kinematics/trtfuncs.c
+++ b/src/emc/kinematics/trtfuncs.c
@@ -362,11 +362,14 @@ int xyzbcKinematicsInverse(const EmcPose * pos,
     const double          dz = hal_get_real(haldata->z_offset) + dt;
     const double       b_rad = pos->b*TO_RAD;
     const double       c_rad = pos->c*TO_RAD;
-    const double         dpx = -cos(b_rad)*dx + sin(b_rad)*dz + dx;
-    const double         dpz = -sin(b_rad)*dx - cos(b_rad)*dz + dz;
 
     rtapi_real con = hal_get_bool(haldata->conventional_directions) ? 1.0 : -1.0;
 
+    // the offsets seen from the tilted table: the same rotation the
+    // forward applies to them, in the same sense
+    const double         dpx = -cos(b_rad)*dx + con * sin(b_rad)*dz + dx;
+    const double         dpz = -con * sin(b_rad)*dx - cos(b_rad)*dz + dz;
+
     EmcPose P; // computed position
 
     P.tran.x   = +       cos(c_rad) * cos(b_rad) * (pos->tran.x - x_rot_point)
diff --git a/src/emc/motion/control.c b/src/emc/motion/control.c
index 50ddadc6c07..b509a133d3e 100644
--- a/src/emc/motion/control.c
+++ b/src/emc/motion/control.c
@@ -363,10 +363,6 @@ static void handle_kinematicsSwitch(void) {
         return; // the kinematics in force is unchanged
     }
 
-    switchkins_type = requested_type;
-    hal_set_real(emcmot_hal_data->kins_type, (double)switchkins_type);
-    emcmotStatus->switchkins_type = switchkins_type;
-
     KINEMATICS_FORWARD_FLAGS tmpFFlags = fflags;
     KINEMATICS_INVERSE_FLAGS tmpIFlags = iflags;
 #ifdef SWITCHKINS_DEBUG
@@ -376,15 +372,25 @@ static void handle_kinematicsSwitch(void) {
         beforePose[anum] = *pcmd_p[anum];
     }
 #endif
+    /* the joints stay where they are, so a kinematics whose forward cannot
+       solve them is one the machine cannot run in from here: put the old
+       one back, or the inverse would run the joints to wherever the pose
+       we know lands in the new one */
     EmcPose poseKinsSwitch = emcmotStatus->carte_pos_cmd;
     if (kinematicsForward(joint_posKinsSwitch, &poseKinsSwitch,
                           &tmpFFlags, &tmpIFlags)) {
-        reportError(_("kinematicsForward failed for kinematics type %d"),
-                    switchkins_type);
+        kinematicsSwitch(switchkins_type);
+        reportError(_("kinematicsForward failed for kinematics type %d,"
+                      " type %d is still in force"),
+                    requested_type, switchkins_type);
         SET_MOTION_ERROR_FLAG(1);  // abort
-        return; // keep the position we know rather than an unsolved one
+        return; // the kinematics in force and the position are unchanged
     }
     emcmotStatus->carte_pos_cmd = poseKinsSwitch;
+
+    switchkins_type = requested_type;
+    hal_set_real(emcmot_hal_data->kins_type, (double)switchkins_type);
+    emcmotStatus->switchkins_type = switchkins_type;
 #ifdef SWITCHKINS_DEBUG
     fprintf(stderr,"kswitch type=%d (%s:%d)\n",switchkins_type,__FUNCTION__,__LINE__);
     for (anum = 0; anum < EMCMOT_MAX_AXIS; anum++) {
diff --git a/src/hal/components/matrixkins.comp b/src/hal/components/matrixkins.comp
index b12dedc2fcf..aac6c04d913 100644
--- a/src/hal/components/matrixkins.comp
+++ b/src/hal/components/matrixkins.comp
@@ -176,6 +176,7 @@ the adjustment values should be added to the old values instead of replacing the
 """;
 see_also "kins(9)";
 pin out bool dummy=1; // halcompile requires at least one pin
+option extra_setup;
 license "GPL";
 ;;
 
@@ -191,15 +192,15 @@ static struct haldata {
     hal_real_t C_zz;
 } *haldata;
 
-static int matrixkins_setup(void) {
+EXTRA_SETUP() {
+    (void)__comp_inst;
+    (void)prefix;
+    (void)extra_arg;
     int res=0;
 
     // inherit comp_id from rtapi_main()
     if (comp_id < 0) goto error;
 
-    res = hal_set_unready(comp_id);
-    if (res) goto error;
-
     haldata = hal_malloc(sizeof(struct haldata));
     if (!haldata) goto error;
 
@@ -215,9 +216,6 @@ static int matrixkins_setup(void) {
 
     if (res) goto error;
 
-    res = hal_ready(comp_id);
-    if (res) goto error;
-
     rtapi_print("*** %s setup ok\n",__FILE__);
     return 0;
 error:
@@ -235,8 +233,6 @@ EXPORT_SYMBOL(kinematicsForward);
 
 KINEMATICS_TYPE kinematicsType()
 {
-    static bool is_setup=0;
-    if (!is_setup) matrixkins_setup();
     return KINEMATICS_BOTH;
 }
 
diff --git a/src/hal/components/millturn.comp b/src/hal/components/millturn.comp
index d1271de882e..45ec650ad96 100644
--- a/src/hal/components/millturn.comp
+++ b/src/hal/components/millturn.comp
@@ -27,9 +27,10 @@ chapter (docs/src/motion/switchkins.txt)
 
 """;
 // The fpin pin is not accessible in kinematics functions.
-// Use the *_setup() function for pins and params used by kinematics.
+// Use EXTRA_SETUP() for pins and params used by kinematics.
 pin out si32 fpin=0"pin to demonstrate use of a conventional (non-kinematics) function fdemo";
 option period no;
+option extra_setup;
 function fdemo;
 license "GPL";
 author "David Mueller";
@@ -59,14 +60,15 @@ FUNCTION(fdemo) {
    fpin_set(fpin + 1);
 }
 
-static int millturn_setup(void) {
+EXTRA_SETUP() {
+    (void)__comp_inst;
+    (void)prefix;
+    (void)extra_arg;
 #define HAL_PREFIX "millturn"
     int res=0;
 
     // inherit comp_id from rtapi_main()
     if (comp_id < 0) goto error;
-    // set unready to allow creation of pins
-    if (hal_set_unready(comp_id)) goto error;
 
     haldata = hal_malloc(sizeof(*haldata));
     if (!haldata) goto error;
@@ -85,7 +87,6 @@ static int millturn_setup(void) {
     res += hal_pin_new_bool(comp_id, HAL_OUT, &haldata->kinstype_is_1, 0, "kinstype.is-1");
 
     if (res) goto error;
-    hal_ready(comp_id);
     rtapi_print("*** %s setup ok\n",__FILE__);
     return 0;
 error:
@@ -142,8 +143,6 @@ int kinematicsSwitch(int new_switchkins_type)
 
 KINEMATICS_TYPE kinematicsType()
 {
-static bool is_setup=0;
-    if (!is_setup) millturn_setup();
     return KINEMATICS_BOTH; // set as required
            // Note: If kinematics are identity, using KINEMATICS_BOTH
            //       may be used in order to allow a gui to display
diff --git a/src/hal/components/userkins.comp b/src/hal/components/userkins.comp
index a2a25d88c29..a7af5d29a75 100644
--- a/src/hal/components/userkins.comp
+++ b/src/hal/components/userkins.comp
@@ -53,14 +53,16 @@ change all instances of `userkins` to `mykins`.
 * The *fpin* pin is included to satisfy the requirements of the halcompile
   utility but it is not accessible to kinematics functions.
 * HAL pins and parameters needed in kinematics functions (kinematicsForward(),
-  kinematicsInverse()) must be setup in a function (*userkins_setup()*) invoked
-  by the initial motion module call to kinematicsType().
+  kinematicsInverse()) must be setup in the *EXTRA_SETUP()* function, which
+  halcompile runs once when the module is loaded, before the component is
+  made ready.
 
 """;
 // The fpin pin is not accessible in kinematics functions.
-// Use the *_setup() function for pins and params used by kinematics.
+// Use EXTRA_SETUP() for pins and params used by kinematics.
 pin out si32 fpin=0"pin to demonstrate use of a conventional (non-kinematics) function fdemo";
 option period no;
+option extra_setup;
 function fdemo;
 license "GPL";
 author "Dewey Garrett";
@@ -91,14 +93,15 @@ FUNCTION(fdemo) {
    fpin_set(fpin + 1);
 }
 
-static int userkins_setup(void) {
+EXTRA_SETUP() {
+    (void)__comp_inst;
+    (void)prefix;
+    (void)extra_arg;
 #define HAL_PREFIX "userkins"
     int res=0;
 
     // inherit comp_id from rtapi_main()
     if (comp_id < 0) goto error;
-    // set unready to allow creation of pins
-    if (hal_set_unready(comp_id)) goto error;
 
     haldata = hal_malloc(sizeof(struct haldata));
     if (!haldata) goto error;
@@ -112,7 +115,6 @@ static int userkins_setup(void) {
     res += hal_param_new_real(comp_id, HAL_RO, &haldata->param_ro, 0.0, "%s.param-ro", HAL_PREFIX);
 
     if (res) goto error;
-    hal_ready(comp_id);
     rtapi_print("*** %s setup ok\n",__FILE__);
     return 0;
 error:
@@ -130,8 +132,6 @@ EXPORT_SYMBOL(kinematicsForward);
 
 KINEMATICS_TYPE kinematicsType()
 {
-static bool is_setup=0;
-    if (!is_setup) userkins_setup();
     return KINEMATICS_IDENTITY; // set as required
            // Note: If kinematics are identity, using KINEMATICS_BOTH
            //       may be used in order to allow a gui to display
diff --git a/src/hal/components/xyzab_tdr_kins.comp b/src/hal/components/xyzab_tdr_kins.comp
index b059f32c103..dd0350e44f7 100644
--- a/src/hal/components/xyzab_tdr_kins.comp
+++ b/src/hal/components/xyzab_tdr_kins.comp
@@ -31,6 +31,7 @@ chapter (docs/src/motion/switchkins.txt)
 """;
 
 pin out si32 dummy=0"one pin needed to satisfy halcompile requirement";
+option extra_setup;
 
 license "GPL";
 author "David Mueller";
@@ -54,13 +55,14 @@ static struct haldata {
   hal_bool_t kinstype_is_1;
 } *haldata;
 
-static int xyzab_tdr_setup(void) {
+EXTRA_SETUP() {
+    (void)__comp_inst;
+    (void)prefix;
+    (void)extra_arg;
 #define HAL_PREFIX "xyzab_tdr_kins"
     int res=0;
     // inherit comp_id from rtapi_main()
     if (comp_id < 0) goto error;
-    // set unready to allow creation of pins
-    if (hal_set_unready(comp_id)) goto error;
 
     haldata = hal_malloc(sizeof(*haldata));
     if (!haldata) goto error;
@@ -80,7 +82,6 @@ static int xyzab_tdr_setup(void) {
     res += hal_pin_new_bool(comp_id, HAL_OUT, &haldata->kinstype_is_1, 0, "kinstype.is-1");
 
     if (res) goto error;
-    hal_ready(comp_id);
     rtapi_print("*** %s setup ok\n",__FILE__);
     return 0;
 error:
@@ -137,8 +138,6 @@ int kinematicsSwitch(int new_switchkins_type)
 
 KINEMATICS_TYPE kinematicsType()
 {
-static bool is_setup=0;
-    if (!is_setup)  xyzab_tdr_setup();
     return KINEMATICS_BOTH; // set as required
            // Note: If kinematics are identity, using KINEMATICS_BOTH
            //       may be used in order to allow a gui to display
diff --git a/tests/kins-switch-unsolved/README b/tests/kins-switch-unsolved/README
new file mode 100644
index 00000000000..c3f263e4f7f
--- /dev/null
+++ b/tests/kins-switch-unsolved/README
@@ -0,0 +1,9 @@
+A kinematics switch whose forward kinematics cannot solve the current
+joint position must leave the type in force, the joints and the position
+alone, report the failure and abort; motion goes on working in the
+kinematics it kept.
+
+The hexapod module starts in identity kinematics here, so the joints are
+put at a few units each as coordinates.  Six struts that short are not a
+platform position the hexapod forward can converge to, so G12.1 P1 asks
+for exactly that switch.
diff --git a/tests/kins-switch-unsolved/checkresult b/tests/kins-switch-unsolved/checkresult
new file mode 100755
index 00000000000..9d48d3f180e
--- /dev/null
+++ b/tests/kins-switch-unsolved/checkresult
@@ -0,0 +1,3 @@
+#!/bin/sh
+# the test script counts its own failures
+grep -q "^Exiting with 0 errors" "$1"
diff --git a/tests/kins-switch-unsolved/sim.hal b/tests/kins-switch-unsolved/sim.hal
new file mode 100644
index 00000000000..e92c60eb526
--- /dev/null
+++ b/tests/kins-switch-unsolved/sim.hal
@@ -0,0 +1,16 @@
+loadrt [KINS]KINEMATICS
+loadrt [EMCMOT]EMCMOT servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[KINS]JOINTS
+
+addf motion-command-handler servo-thread
+addf motion-controller servo-thread
+
+net J0 joint.0.motor-pos-cmd => joint.0.motor-pos-fb
+net J1 joint.1.motor-pos-cmd => joint.1.motor-pos-fb
+net J2 joint.2.motor-pos-cmd => joint.2.motor-pos-fb
+net J3 joint.3.motor-pos-cmd => joint.3.motor-pos-fb
+net J4 joint.4.motor-pos-cmd => joint.4.motor-pos-fb
+net J5 joint.5.motor-pos-cmd => joint.5.motor-pos-fb
+
+net estop-loop iocontrol.0.user-enable-out iocontrol.0.emc-enable-in
+net tool-prep-loop iocontrol.0.tool-prepare iocontrol.0.tool-prepared
+net tool-change-loop iocontrol.0.tool-change iocontrol.0.tool-changed
diff --git a/tests/kins-switch-unsolved/test-ui.py b/tests/kins-switch-unsolved/test-ui.py
new file mode 100755
index 00000000000..1995bcd1e23
--- /dev/null
+++ b/tests/kins-switch-unsolved/test-ui.py
@@ -0,0 +1,112 @@
+#!/usr/bin/env python3
+# A kinematics switch the new forward cannot solve.  Motion must keep the
+# position it knows, say so, abort, and take a switch back afterwards.
+import hal
+import linuxcnc
+import sys
+import time
+
+c = linuxcnc.command()
+s = linuxcnc.stat()
+e = linuxcnc.error_channel()
+
+errors = 0
+
+def error(what):
+    global errors
+    errors += 1
+    print("*** ERROR %s" % what)
+
+def kins_type():
+    return int(hal.get_value("motion.kins-type"))
+
+def position():
+    s.poll()
+    return tuple(round(v, 6) for v in s.position[:6])
+
+def drain():
+    said = []
+    while True:
+        m = e.poll()
+        if not m:
+            return said
+        said.append(m[1])
+
+def wait_idle():
+    deadline = time.time() + 30
+    while time.time() < deadline:
+        s.poll()
+        if s.interp_state == linuxcnc.INTERP_IDLE and not s.queue:
+            return
+        time.sleep(0.05)
+    error("timed out waiting for the interpreter")
+
+def mdi(cmd):
+    c.mdi(cmd)
+    c.wait_complete(30)
+    wait_idle()
+    time.sleep(0.2)   # let the error channel and the status catch up
+
+c.state(linuxcnc.STATE_ESTOP_RESET)
+c.state(linuxcnc.STATE_ON)
+c.wait_complete(30)
+c.home(-1)
+c.wait_complete(60)
+c.mode(linuxcnc.MODE_MDI)
+c.wait_complete(30)
+drain()
+
+if kins_type() != 0:
+    error("starts in kinematics type %d, expected identity (0)" % kins_type())
+
+def joints():
+    s.poll()
+    return tuple(round(v, 6) for v in s.joint_position[:6])
+
+# a known position, in identity: joints and coordinates are the same thing
+mdi("G0 X1 Y2 Z3 A4 B5 C6")
+before = position()
+if before != (1, 2, 3, 4, 5, 6):
+    error("position before the switch is %s, expected (1, 2, 3, 4, 5, 6)" % (before,))
+drain()
+
+# the switch the hexapod forward cannot solve: six struts of a few units
+# are no platform position.  Nothing may change but the report.
+mdi("G12.1 P1")
+said = drain()
+if not any("kinematicsForward failed" in m for m in said):
+    error("no report of the failed forward kinematics, got %s" % said)
+if kins_type() != 0:
+    error("kinematics type %d after the failed switch, expected 0 still" % kins_type())
+if position() != before:
+    error("position after the failed switch is %s, expected %s unchanged" % (position(), before))
+if joints() != before:
+    error("joints after the failed switch are %s, expected %s unchanged" % (joints(), before))
+s.poll()
+if s.task_state != linuxcnc.STATE_ON:
+    error("task state %d after the failed switch, expected still ON" % s.task_state)
+
+# motion goes on working in the kinematics it kept, and the module is
+# back in it too: the joints follow the identity inverse, not the hexapod's
+c.mode(linuxcnc.MODE_MDI)
+c.wait_complete(30)
+mdi("G0 X30 Y30 Z30 A30 B30 C30")
+if joints() != (30, 30, 30, 30, 30, 30):
+    error("joints after the move are %s, expected all 30" % (joints(),))
+said = drain()
+if said:
+    error("unexpected messages after the failed switch: %s" % said)
+
+# a switch to the kinematics in force is nothing to do
+mdi("G13.1")
+if kins_type() != 0:
+    error("kinematics type %d after G13.1, expected identity (0)" % kins_type())
+if position() != (30, 30, 30, 30, 30, 30):
+    error("position after G13.1 is %s, expected all 30" % (position(),))
+said = drain()
+if said:
+    error("unexpected messages after the switch back: %s" % said)
+
+print("Exiting with %d errors" % errors)
+c.state(linuxcnc.STATE_ESTOP)
+sys.exit(1 if errors else 0)
diff --git a/tests/kins-switch-unsolved/test.ini b/tests/kins-switch-unsolved/test.ini
new file mode 100644
index 00000000000..c93bc09563f
--- /dev/null
+++ b/tests/kins-switch-unsolved/test.ini
@@ -0,0 +1,130 @@
+[EMC]
+VERSION = 1.1
+DEBUG = 0
+
+[DISPLAY]
+DISPLAY = ./test-ui.py
+
+[RS274NGC]
+RS274NGC_STARTUP_CODE = G17 G21 G40 G49 G54 G64 P0.001 G80 G90 G92.1 G94 G97 G98
+PARAMETER_FILE = sim.var
+
+[KINS]
+# switchkins-type 0 is identity, 1 is the hexapod, 2 is the userk template
+KINEMATICS = genhexkins sparm=identityfirst
+JOINTS = 6
+
+[HAL]
+HALFILE = sim.hal
+
+[TRAJ]
+COORDINATES = XYZABC
+LINEAR_UNITS = mm
+ANGULAR_UNITS = deg
+DEFAULT_LINEAR_VELOCITY = 200
+MAX_LINEAR_VELOCITY = 346
+MAX_LINEAR_ACCELERATION = 800
+DEFAULT_LINEAR_ACCELERATION = 800
+MAX_ANGULAR_VELOCITY = 360
+
+[EMCMOT]
+EMCMOT = motmod
+SERVO_PERIOD = 1000000
+COMM_TIMEOUT = 4
+
+[TASK]
+TASK = milltask
+CYCLE_TIME = 0.010
+
+[EMCIO]
+TOOL_TABLE = tool.tbl
+
+[AXIS_X]
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 200
+MAX_ACCELERATION = 800
+
+[AXIS_Y]
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 200
+MAX_ACCELERATION = 800
+
+[AXIS_Z]
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 200
+MAX_ACCELERATION = 800
+
+[AXIS_A]
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 60
+MAX_ACCELERATION = 200
+
+[AXIS_B]
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 60
+MAX_ACCELERATION = 200
+
+[AXIS_C]
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 60
+MAX_ACCELERATION = 200
+
+[JOINT_0]
+TYPE = LINEAR
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 200
+MAX_ACCELERATION = 800
+HOME_SEARCH_VEL = 0
+HOME_SEQUENCE = 0
+
+[JOINT_1]
+TYPE = LINEAR
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 200
+MAX_ACCELERATION = 800
+HOME_SEARCH_VEL = 0
+HOME_SEQUENCE = 0
+
+[JOINT_2]
+TYPE = LINEAR
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 200
+MAX_ACCELERATION = 800
+HOME_SEARCH_VEL = 0
+HOME_SEQUENCE = 0
+
+[JOINT_3]
+TYPE = ANGULAR
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 60
+MAX_ACCELERATION = 200
+HOME_SEARCH_VEL = 0
+HOME_SEQUENCE = 0
+
+[JOINT_4]
+TYPE = ANGULAR
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 60
+MAX_ACCELERATION = 200
+HOME_SEARCH_VEL = 0
+HOME_SEQUENCE = 0
+
+[JOINT_5]
+TYPE = ANGULAR
+MIN_LIMIT = -500
+MAX_LIMIT = 500
+MAX_VELOCITY = 60
+MAX_ACCELERATION = 200
+HOME_SEARCH_VEL = 0
+HOME_SEQUENCE = 0
diff --git a/tests/kins-switch-unsolved/test.sh b/tests/kins-switch-unsolved/test.sh
new file mode 100755
index 00000000000..765cf14fed6
--- /dev/null
+++ b/tests/kins-switch-unsolved/test.sh
@@ -0,0 +1,4 @@
+#!/bin/bash -e
+# a failed run leaves the var file behind, and it carries offsets
+rm -f sim.var sim.var.bak
+linuxcnc -r test.ini
diff --git a/tests/kins-switch-unsolved/tool.tbl b/tests/kins-switch-unsolved/tool.tbl
new file mode 100644
index 00000000000..d793e2d60ed
--- /dev/null
+++ b/tests/kins-switch-unsolved/tool.tbl
@@ -0,0 +1 @@
+T1 P1 D0.0 Z12.5 ;
diff --git a/tests/maxkins/README b/tests/maxkins/README
new file mode 100644
index 00000000000..cdf964410db
--- /dev/null
+++ b/tests/maxkins/README
@@ -0,0 +1,7 @@
+Tests that maxkins forward and inverse kinematics agree with each other.
+
+The machine is driven to a series of poses with the pivot length, the tool
+length and every one of B, C, U, V and W away from zero, and the position
+that comes back through the forward kinematics is compared with the one that
+was commanded.  A pose that survives the round trip is one where the two
+directions of the transform describe the same machine.
diff --git a/tests/maxkins/checkresult b/tests/maxkins/checkresult
new file mode 100755
index 00000000000..24dc9aa53e3
--- /dev/null
+++ b/tests/maxkins/checkresult
@@ -0,0 +1,2 @@
+#!/bin/sh
+exit 0 # test failure is indicated by test.sh exit value
diff --git a/tests/maxkins/core_sim.hal b/tests/maxkins/core_sim.hal
new file mode 100644
index 00000000000..daf9b8f4c25
--- /dev/null
+++ b/tests/maxkins/core_sim.hal
@@ -0,0 +1,28 @@
+# core HAL config file for simulation
+
+loadrt [KINS]KINEMATICS
+loadrt [EMCMOT]EMCMOT servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[KINS]JOINTS
+
+# add motion controller functions to servo thread
+addf motion-command-handler servo-thread
+addf motion-controller servo-thread
+
+# create HAL signals for position commands from motion module
+# loop position commands back to motion module feedback
+net Xpos joint.0.motor-pos-cmd => joint.0.motor-pos-fb
+net Ypos joint.1.motor-pos-cmd => joint.1.motor-pos-fb
+net Zpos joint.2.motor-pos-cmd => joint.2.motor-pos-fb
+net Apos joint.3.motor-pos-cmd => joint.3.motor-pos-fb
+net Bpos joint.4.motor-pos-cmd => joint.4.motor-pos-fb
+net Cpos joint.5.motor-pos-cmd => joint.5.motor-pos-fb
+net Upos joint.6.motor-pos-cmd => joint.6.motor-pos-fb
+net Vpos joint.7.motor-pos-cmd => joint.7.motor-pos-fb
+net Wpos joint.8.motor-pos-cmd => joint.8.motor-pos-fb
+
+# the geometry the kinematics works from.  Both are away from zero so that
+# the pivot to tip distance is not degenerate.
+setp maxkins.pivot-length [MAX]B_PIVOT_LENGTH
+setp maxkins.tool-length  [MAX]TOOL_LENGTH
+
+# estop loopback
+net estop-loop iocontrol.0.user-enable-out iocontrol.0.emc-enable-in
diff --git a/tests/maxkins/test-ui.py b/tests/maxkins/test-ui.py
new file mode 100755
index 00000000000..d65e561e516
--- /dev/null
+++ b/tests/maxkins/test-ui.py
@@ -0,0 +1,132 @@
+#!/usr/bin/env python3
+
+import linuxcnc
+import hal
+
+import time
+import sys
+
+
+def wait_for_linuxcnc_startup(status, timeout=10.0):
+
+    """Poll the Status buffer waiting for it to look initialized,
+    rather than just allocated (all-zero).  Returns on success, throws
+    RuntimeError on failure."""
+
+    start_time = time.time()
+    while time.time() - start_time < timeout:
+        status.poll()
+        if (status.angular_units == 0.0) \
+            or (status.axis_mask == 0) \
+            or (status.cycle_time == 0.0) \
+            or (status.exec_state != linuxcnc.EXEC_DONE) \
+            or (status.interp_state != linuxcnc.INTERP_IDLE) \
+            or (status.inpos == False) \
+            or (status.linear_units == 0.0) \
+            or (status.max_acceleration == 0.0) \
+            or (status.max_velocity == 0.0) \
+            or (status.program_units == 0.0) \
+            or (status.rapidrate == 0.0) \
+            or (status.state != linuxcnc.RCS_DONE) \
+            or (status.task_state != linuxcnc.STATE_ESTOP):
+            time.sleep(0.1)
+        else:
+            # looks good
+            return
+
+    # timeout, throw an exception
+    raise RuntimeError("Timeout")
+
+
+c = linuxcnc.command()
+s = linuxcnc.stat()
+e = linuxcnc.error_channel()
+
+# Wait for LinuxCNC to initialize itself so the Status buffer stabilizes.
+wait_for_linuxcnc_startup(s)
+
+# Because the kinematics is non-trivial, a homing is needed.
+# HOME_ABSOLUTE_ENCODER = 1 is used in the ini file.
+c.state(linuxcnc.STATE_ESTOP_RESET)
+c.state(linuxcnc.STATE_ON)
+for joint in range(9):
+    c.home(joint)
+c.wait_complete()
+
+LETTERS = 'XYZABCUVW'
+
+
+def absdelta(a, b):
+    '''Maximum absolute difference between components of two coordinate points'''
+    return max(abs(a[i] - b[i]) for i in range(len(a)))
+
+
+def test_pose(pose):
+    '''Command LinuxCNC to go to 'pose', then check that the position that
+    comes back matches it.  Motion runs the inverse kinematics to turn the
+    pose into joint values and the forward kinematics to turn the joint
+    feedback back into a position, so a pose that comes back unchanged is one
+    the two directions agree on.
+    '''
+    words = ' '.join('%s%0.9f' % (letter, value)
+                     for letter, value in zip(LETTERS, pose))
+
+    c.mode(linuxcnc.MODE_MDI)
+    c.mdi('G0 ' + words)
+    c.wait_complete()
+
+    # The delay seems to be needed for trajectory to fully settle, otherwise
+    # there is about 1e-5 error between target and actual position.
+    time.sleep(0.05)
+    s.poll()
+    joints = s.joint_actual_position[:9]
+    position = s.actual_position[:9]
+
+    print("Commanded %s, joints %s, position %s" % (pose, joints, position))
+
+    # Accuracy limit is set to 1e-9 here.
+    # For practical purposes, a numerical accuracy of 1e-6 would be perfectly
+    # acceptable.  Current implementation using doubles achieves about 1e-14
+    # precision.
+    if absdelta(position, pose) > 1e-9:
+        raise RuntimeError(
+            "Forward and inverse kinematics disagree: commanded %s, joints %s, got %s"
+            % (pose, joints, position))
+
+
+#                X    Y    Z    A    B    C    U    V    W
+POSES = [
+    # The pose everything starts from.
+    (       0,   0,   0,   0,   0,   0,   0,   0,   0),
+    # Linear axes only, with the head upright.
+    (      10,  20,  30,   0,   0,   0,   0,   0,   0),
+    # B alone tilts the head, which moves the tip in X and Z.
+    (      10,  20,  30,   0,  40,   0,   0,   0,   0),
+    # C alone turns the table under the tip.
+    (      10,  20,  30,   0,   0,  30,   0,   0,   0),
+    # B and C together: the head correction is in the machine frame and the
+    # table rotation is not, so the order the two are applied in matters.
+    (      10,  20,  30,   0,  40,  30,   0,   0,   0),
+    # U alone shifts the head along its own axis, which with B tilted has a
+    # component in both X and Z.
+    (      10,  20,  30,   0,  40,   0,  15,   0,   0),
+    # V is a plain shift of the saddle.
+    (      10,  20,  30,   0,  40,   0,   0,   8,   0),
+    # W extends the pivot to tip distance.
+    (      10,  20,  30,   0,  40,   0,   0,   0,  12),
+    # Everything at once.
+    (      50,  50,  50,   5,  40,  30,  15,   8,  12),
+    # And with the signs the other way round.
+    (     -50, -50, -50,  -5, -40, -30, -15,  -8, -12),
+    # Back to the origin, where the pose is the same whichever direction the
+    # axes are taken to run in.
+    (       0,   0,   0,   0,   0,   0,   0,   0,   0),
+]
+
+for conventional in (0, 1):
+    hal.set_p('maxkins.conventional-directions', str(conventional))
+    print("conventional-directions %d" % conventional)
+    for pose in POSES:
+        test_pose(pose)
+
+sys.exit(0)
diff --git a/tests/maxkins/test.ini b/tests/maxkins/test.ini
new file mode 100644
index 00000000000..7cf23c05738
--- /dev/null
+++ b/tests/maxkins/test.ini
@@ -0,0 +1,210 @@
+[EMC]
+# The version string for this INI file.
+VERSION = 1.1
+
+DEBUG = 0
+
+[MAX]
+# distance from the end of the reference tool to the centre of the head
+# tilt axis, and the length of the tool on top of it
+B_PIVOT_LENGTH = 100
+TOOL_LENGTH = 25
+
+[DISPLAY]
+DISPLAY = ./test-ui.py
+
+[FILTER]
+#No Content
+
+[RS274NGC]
+PARAMETER_FILE = sim.var
+
+[EMCMOT]
+EMCMOT = motmod
+COMM_TIMEOUT = 4.0
+BASE_PERIOD = 0
+SERVO_PERIOD = 1000000
+
+[TASK]
+TASK = milltask
+CYCLE_TIME = 0.001
+
+[HAL]
+HALUI = halui
+HALFILE = core_sim.hal
+
+[HALUI]
+#No Content
+
+[TRAJ]
+COORDINATES =           X Y Z A B C U V W
+HOME =                  0 0 0 0 0 0 0 0 0
+LINEAR_UNITS =          mm
+ANGULAR_UNITS =         degree
+DEFAULT_LINEAR_VELOCITY =       10
+MAX_LINEAR_VELOCITY =          100
+MAX_LINEAR_ACCELERATION =     1000
+DEFAULT_ANGULAR_VELOCITY =      10
+MAX_ANGULAR_VELOCITY =         100
+MAX_ANGULAR_ACCELERATION =    1000
+
+[EMCIO]
+TOOL_TABLE = tool.tbl
+RANDOM_TOOLCHANGER = 0
+
+[KINS]
+KINEMATICS = maxkins
+JOINTS = 9
+
+[AXIS_X]
+MIN_LIMIT = -1000
+MAX_LIMIT = 1000
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_0]
+TYPE =             LINEAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -1000
+MAX_LIMIT =        1000
+FERROR =           0.001
+
+[AXIS_Y]
+MIN_LIMIT = -1000
+MAX_LIMIT = 1000
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_1]
+TYPE =             LINEAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -1000
+MAX_LIMIT =        1000
+FERROR =           0.001
+
+[AXIS_Z]
+MIN_LIMIT = -1000
+MAX_LIMIT = 1000
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_2]
+TYPE =             LINEAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -1000
+MAX_LIMIT =        1000
+FERROR =           0.001
+
+[AXIS_A]
+MIN_LIMIT = -360
+MAX_LIMIT = 360
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_3]
+TYPE =             ANGULAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -360
+MAX_LIMIT =        360
+FERROR =           0.001
+
+[AXIS_B]
+MIN_LIMIT = -360
+MAX_LIMIT = 360
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_4]
+TYPE =             ANGULAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -360
+MAX_LIMIT =        360
+FERROR =           0.001
+
+[AXIS_C]
+MIN_LIMIT = -360
+MAX_LIMIT = 360
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_5]
+TYPE =             ANGULAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -360
+MAX_LIMIT =        360
+FERROR =           0.001
+
+[AXIS_U]
+MIN_LIMIT = -1000
+MAX_LIMIT = 1000
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_6]
+TYPE =             LINEAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -1000
+MAX_LIMIT =        1000
+FERROR =           0.001
+
+[AXIS_V]
+MIN_LIMIT = -1000
+MAX_LIMIT = 1000
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_7]
+TYPE =             LINEAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -1000
+MAX_LIMIT =        1000
+FERROR =           0.001
+
+[AXIS_W]
+MIN_LIMIT = -1000
+MAX_LIMIT = 1000
+MAX_VELOCITY = 100
+MAX_ACCELERATION = 1000
+
+[JOINT_8]
+TYPE =             LINEAR
+HOME =             0.000
+HOME_ABSOLUTE_ENCODER = 1
+MAX_VELOCITY =     100
+MAX_ACCELERATION = 1000
+BACKLASH =         0.000
+MIN_LIMIT =        -1000
+MAX_LIMIT =        1000
+FERROR =           0.001
diff --git a/tests/maxkins/test.sh b/tests/maxkins/test.sh
new file mode 100755
index 00000000000..6edf34d77ca
--- /dev/null
+++ b/tests/maxkins/test.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+
+rm -f sim.var
+linuxcnc -r test.ini
diff --git a/tests/maxkins/tool.tbl b/tests/maxkins/tool.tbl
new file mode 100644
index 00000000000..e69de29bb2d