Motion: test low-level enable changes via GPIO stub

This fixes the driver's enable/disable incorrectly setting the direction
bit instead.

src/hal/avr/tmc2130.cpp

@@ -74,7 +74,7 @@ void TMC2130::SetCurrents(const MotorParams &params, const MotorCurrents &curren
 }
 
 void TMC2130::SetEnabled(const MotorParams &params, bool enabled) {
-    hal::shr16::shr16.SetTMCDir(params.idx, enabled);
+    hal::shr16::shr16.SetTMCEnabled(params.idx, enabled);
     if (this->enabled != enabled)
         ClearStallguard(params);
     this->enabled = enabled;

tests/unit/modules/motion/test_motion.cpp

@@ -3,6 +3,17 @@
 
 using namespace modules::motion;
 
+namespace hal {
+namespace shr16 {
+extern uint8_t shr16_tmc_ena;
+} // namespace shr16
+} // namespace hal
+
+// Conveniently read the enable state set into the lower-level shift register
+bool getTMCEnabled(const MotorParams &mp) {
+    return (hal::shr16::shr16_tmc_ena & (1 << mp.idx));
+}
+
 // Perform Step() until all moves are completed, returning the number of steps performed.
 // Ensure the move doesn't run forever, making the test fail reliably.
 ssize_t stepUntilDone(size_t maxSteps = 100000) {
@@ -34,19 +45,23 @@ TEST_CASE("motion::basic", "[motion]") {
 TEST_CASE("motion::auto_axis_enable", "[motion]") {
     // by default the axis should start disabled
     REQUIRE(motion.Enabled(Pulley) == false);
+    REQUIRE(getTMCEnabled(axisParams[Pulley].params) == false);
 
     // enable manually the axis
     motion.SetEnabled(Pulley, true);
     REQUIRE(motion.Enabled(Pulley) == true);
+    REQUIRE(getTMCEnabled(axisParams[Pulley].params) == true);
 
     // now disable
     motion.SetEnabled(Pulley, false);
     REQUIRE(motion.Enabled(Pulley) == false);
+    REQUIRE(getTMCEnabled(axisParams[Pulley].params) == false);
 
     // planning a move should enable the axis automatically
     REQUIRE(motion.QueueEmpty());
     motion.PlanMove<Pulley>(1.0_mm, 100.0_mm_s);
     REQUIRE(motion.Enabled(Pulley) == true);
+    REQUIRE(getTMCEnabled(axisParams[Pulley].params) == true);
 }
 
 TEST_CASE("motion::unit", "[motion]") {

tests/unit/modules/stubs/stub_shr16.cpp

@@ -7,10 +7,12 @@ SHR16 shr16;
 
 uint16_t shr16_v_copy;
 uint8_t shr16_tmc_dir;
+uint8_t shr16_tmc_ena;
 
 void SHR16::Init() {
     shr16_v_copy = 0;
     shr16_tmc_dir = 0;
+    shr16_tmc_ena = 0;
 }
 
 void SHR16::SetLED(uint16_t led) {
@@ -18,7 +20,11 @@ void SHR16::SetLED(uint16_t led) {
 }
 
 void SHR16::SetTMCEnabled(uint8_t index, bool ena) {
-    // do nothing right now
+    // this is using another array for testing convenience
+    if (ena)
+        shr16_tmc_ena |= (1 << index);
+    else
+        shr16_tmc_ena &= ~(1 << index);
 }
 
 void SHR16::SetTMCDir(uint8_t index, bool dir) {