AP_HAL: add bitwidth hal definitions.

revert to original bitwidths for neopixel and profiled
add proper neopixel test that observes spec'ed timings

libraries/AP_HAL/RCOutput.h

@@ -319,6 +319,21 @@ public:
      */
     static uint32_t calculate_bitrate_prescaler(uint32_t timer_clock, uint32_t target_frequency, bool is_dshot);
 
+    /*
+     * bit width values for different protocols
+     */
+    static constexpr uint32_t DSHOT_BIT_WIDTH_TICKS = 8;
+    static constexpr uint32_t DSHOT_BIT_0_TICKS = 3;
+    static constexpr uint32_t DSHOT_BIT_1_TICKS = 6;
+
+    // See WS2812B spec for expected pulse widths
+    static constexpr uint32_t NEOP_BIT_WIDTH_TICKS = 20;
+    static constexpr uint32_t NEOP_BIT_0_TICKS = 7;
+    static constexpr uint32_t NEOP_BIT_1_TICKS = 14;
+    // neopixel does not use pulse widths at all
+    static constexpr uint32_t PROFI_BIT_0_TICKS = 7;
+    static constexpr uint32_t PROFI_BIT_1_TICKS = 14;
+
 protected:
 
     // helper functions for implementation of get_output_mode_banner

libraries/AP_HAL/tests/test_prescaler.cpp

@@ -11,24 +11,41 @@ protected:
         const uint32_t prescaler = AP_HAL::RCOutput::calculate_bitrate_prescaler(clock, target_rate, is_dshot);
         // we would like at most a 1% discrepancy in target versus actual
         const float rate_delta = fabsf(float(clock / prescaler) - target_rate) / target_rate;
-        EXPECT_TRUE(rate_delta < 0.13f);
+        // hack because CUAV_GPS does not support dshot
+        const float expected_delta = clock > 50000000 ? 0.13f : 0.35f;
+        EXPECT_TRUE(rate_delta < expected_delta);
+    }
+
+    void test_prescaler_neopixel(uint32_t clock)
+    {
+        const uint32_t target_rate = 800000 * AP_HAL::RCOutput::NEOP_BIT_WIDTH_TICKS;
+        const uint32_t prescaler = AP_HAL::RCOutput::calculate_bitrate_prescaler(clock, target_rate, false);
+        const uint32_t actual_rate = clock / prescaler;
+
+        const float bit_1_width_us = 1000000.0f * AP_HAL::RCOutput::NEOP_BIT_1_TICKS / actual_rate;
+        const float bit_0_width_us = 1000000.0f * AP_HAL::RCOutput::NEOP_BIT_0_TICKS / actual_rate;
+
+        // timing requirements from WS2812B spec
+        EXPECT_TRUE(bit_1_width_us < (0.85f + 0.15f) && bit_1_width_us > (0.85f - 0.15f));
+        EXPECT_TRUE(bit_0_width_us < (0.4f + 0.15f) && bit_0_width_us > (0.4f - 0.15f));
+        EXPECT_TRUE((bit_0_width_us + bit_1_width_us) < (1.25f + 0.6f) && (bit_0_width_us + bit_1_width_us) > (1.25f - 0.6f));
     }
 };
 
 TEST_P(PrescalerParameterizedTestFixture, DShot150) {
-    test_prescaler(GetParam(), 150000 * 8, true);
+    test_prescaler(GetParam(), 150000 * AP_HAL::RCOutput::DSHOT_BIT_WIDTH_TICKS, true);
 }
 
 TEST_P(PrescalerParameterizedTestFixture, DShot300) {
-    test_prescaler(GetParam(), 300000 * 8, true);
+    test_prescaler(GetParam(), 300000 * AP_HAL::RCOutput::DSHOT_BIT_WIDTH_TICKS, true);
 }
 
 TEST_P(PrescalerParameterizedTestFixture, DShot600) {
-    test_prescaler(GetParam(), 600000 * 8, true);
+    test_prescaler(GetParam(), 600000 * AP_HAL::RCOutput::DSHOT_BIT_WIDTH_TICKS, true);
 }
 
 TEST_P(PrescalerParameterizedTestFixture, DShot1200) {
-    test_prescaler(GetParam(), 1200000 * 8, true);
+    test_prescaler(GetParam(), 1200000 * AP_HAL::RCOutput::DSHOT_BIT_WIDTH_TICKS, true);
 }
 
 TEST_P(PrescalerParameterizedTestFixture, Passthrough) {
@@ -36,11 +53,11 @@ TEST_P(PrescalerParameterizedTestFixture, Passthrough) {
 }
 
 TEST_P(PrescalerParameterizedTestFixture, NeoPixel) {
-    test_prescaler(GetParam(), 800000 * 11, false);
+    test_prescaler_neopixel(GetParam());
 }
 
 TEST_P(PrescalerParameterizedTestFixture, ProfiLED) {
-    test_prescaler(GetParam(), 1500000 * 11, false);
+    test_prescaler(GetParam(), 1500000 * AP_HAL::RCOutput::NEOP_BIT_WIDTH_TICKS, false);
 }
 
 INSTANTIATE_TEST_CASE_P(
@@ -51,7 +68,8 @@ INSTANTIATE_TEST_CASE_P(
                 216000000,  // F745
                 108000000,  // F745
                  84000000,  // F405
-                168000000   // F405
+                168000000,  // F405
+                 50000000   // CUAV_GPS
         ));
 
 AP_GTEST_MAIN()