Added code to measure latency with an oscilloscope.

Both the GTG latency and the ground station in isolation can be measured.
Oscilloscope required.

Author: jeanlemotan

air_firmware/main/main.cpp

@@ -992,11 +992,21 @@ IRAM_ATTR static void wifi_tx_proc(void *)
                         //xSemaphoreTake(s_wifi_tx_done_semaphore, portMAX_DELAY); //wait for the tx_done notification
 #endif
                     }
-                    else
+                    else if (res == ESP_ERR_NO_MEM) //No TX buffers available, need to poll.
                     {
                         spins++;
-                        if (spins > 10000)
+                        if (spins > 1000)
                             vTaskDelay(1);
+                        else
+                            taskYIELD();
+                    }
+                    else //other errors
+                    {
+                        //LOG("Wlan err: %d\n", res);
+                        s_stats.wlan_error_count++;
+                        xSemaphoreTake(s_wlan_outgoing_mux, portMAX_DELAY);
+                        end_reading_wlan_outgoing_packet(packet);
+                        xSemaphoreGive(s_wlan_outgoing_mux);
                     }
                 }
             }
@@ -1084,9 +1094,9 @@ void setup_wifi()
         xSemaphoreGive(s_fec_encoder_mux);
 
         Fec_Codec::Descriptor descriptor;
-        descriptor.coding_k = 4;
-        descriptor.coding_n = 7;
-        descriptor.mtu = AIR2GROUND_MTU;
+        descriptor.coding_k = s_ground2air_config_packet.fec_codec_k;
+        descriptor.coding_n = s_ground2air_config_packet.fec_codec_n;
+        descriptor.mtu = s_ground2air_config_packet.fec_codec_mtu;
         descriptor.core = Fec_Codec::Core::Any;
         descriptor.priority = 1;
         xSemaphoreTake(s_fec_encoder_mux, portMAX_DELAY);

air_firmware/main/main.h

@@ -6,7 +6,7 @@
 /////////////////////////////////////////////////////////////////////////
 
 constexpr size_t WLAN_INCOMING_BUFFER_SIZE = 1024;
-constexpr size_t WLAN_OUTGOING_BUFFER_SIZE = 32768;
+constexpr size_t WLAN_OUTGOING_BUFFER_SIZE = 70000;
 
 ////////////////////////////////////////////////////////////////////////////////////
 

components/common/packets.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include "structures.h"
+
 #pragma pack(push, 1) // exact fit - no padding
 
 enum class WIFI_Rate : uint8_t
@@ -38,7 +40,7 @@ enum class WIFI_Rate : uint8_t
     /* 29 */ RATE_N_72M_MCS7_S,
 };
 
-static constexpr size_t AIR2GROUND_MTU = 1400;
+static constexpr size_t AIR2GROUND_MTU = WLAN_MAX_PAYLOAD_SIZE - 6; //6 is the fec header size
 
 ///////////////////////////////////////////////////////////////////////////////////////
 
@@ -79,8 +81,8 @@ struct Ground2Air_Config_Packet : Ground2Air_Header
     uint8_t ping = 0; //used for latency measurement
     int8_t wifi_power = 20;//dBm
     WIFI_Rate wifi_rate = WIFI_Rate::RATE_G_18M_ODFM;
-    uint8_t fec_codec_k = 4;
-    uint8_t fec_codec_n = 7;
+    uint8_t fec_codec_k = 2;
+    uint8_t fec_codec_n = 3;
     uint16_t fec_codec_mtu = AIR2GROUND_MTU;
     bool dvr_record = false;
 

gs/.vscode/settings.json

@@ -70,6 +70,7 @@
         "utility": "cpp",
         "__tree": "cpp",
         "map": "cpp",
-        "set": "cpp"
+        "set": "cpp",
+        "condition_variable": "cpp"
     }
 }

gs/Makefile

@@ -67,7 +67,7 @@ CPPFLAGS := -O3 -DNDEBUG -ffast-math -funroll-loops -mcpu=cortex-a8 -mfpu=neon -
 # linker flags
 #LDFLAGS := -L/usr/lib -L=/opt/vc/lib -lstdc++ -lm -lpthread -lz -lrt -lfreetype -lmmal_core -lmmal_util -lmmal_vc_client -lvcos -lbcm_host -lbrcmGLESv2 -lbrcmEGL -lts
 #LDFLAGS := -L/usr/lib -L=/opt/vc/lib -lstdc++ -lm -lpthread -lz -lrt -lfreetype -lSDL2 -lGLESv2 -lturbojpeg -lmmal_core -lmmal_util -lmmal_vc_client -lvcos -lepoxy
-LDFLAGS := -L/usr/lib -L=/opt/vc/lib -lstdc++ -lm -lpthread -lz -lrt -lfreetype -lSDL2 -lturbojpeg -lpcap -lGLESv2
+LDFLAGS := -L/usr/lib -L=/opt/vc/lib -lstdc++ -lm -lpthread -lz -lrt -lfreetype -lSDL2 -lturbojpeg -lpcap -lGLESv2 -lpigpio
 # flags required for dependency generation; passed to compilers
 DEPFLAGS = -MT $@ -MD -MP -MF $(DEPDIR)/$*.Td
 

gs/src/PI_HAL.cpp

@@ -4,7 +4,7 @@
 #define USE_SDL
 //#define USE_MANGA_SCREEN2
 
-#define USE_BOUBLE_BUFFER
+//#define USE_BOUBLE_BUFFER
 
 #include <fstream>
 #include <future>
@@ -39,7 +39,7 @@ extern "C"
 
 extern "C"
 {
-//#include "pigpio.h"
+#include "pigpio.h"
 }
 
 extern uint8_t s_font_droid_sans[];
@@ -102,7 +102,7 @@ struct PI_HAL::Impl
     };
     std::array<Touch, MAX_TOUCHES> touches;
 
-    //bool pigpio_is_isitialized = false;
+    bool pigpio_is_isitialized = false;
     float target_backlight = 1.0f;
     float backlight = 0.0f;
 
@@ -117,38 +117,38 @@ struct PI_HAL::Impl
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 
-// bool PI_HAL::init_pigpio()
-// {
-//     if (m_impl->pigpio_is_isitialized)
-//         return true;
+bool PI_HAL::init_pigpio()
+{
+    if (m_impl->pigpio_is_isitialized)
+        return true;
 
-//     LOGI("Initializing pigpio");
-//     if (gpioCfgClock(2, PI_CLOCK_PCM, 0) < 0 ||
-//             gpioCfgPermissions(static_cast<uint64_t>(-1)))
-//     {
-//         LOGE("Cannot configure pigpio");
-//         return false;
-//     }
-//     if (gpioInitialise() < 0)
-//     {
-//         LOGE("Cannot init pigpio");
-//         return false;
-//     }
+    LOGI("Initializing pigpio");
+    if (gpioCfgClock(2, PI_CLOCK_PCM, 0) < 0 ||
+            gpioCfgPermissions(static_cast<uint64_t>(-1)))
+    {
+        LOGE("Cannot configure pigpio");
+        return false;
+    }
+    if (gpioInitialise() < 0)
+    {
+        LOGE("Cannot init pigpio");
+        return false;
+    }
 
-//     m_impl->pigpio_is_isitialized = true;
+    m_impl->pigpio_is_isitialized = true;
 
-//     return true;
-// }
+    return true;
+}
 
 // ///////////////////////////////////////////////////////////////////////////////////////////////////
 
-// void PI_HAL::shutdown_pigpio()
-// {
-//     if (m_impl->pigpio_is_isitialized)
-//         gpioTerminate();
+void PI_HAL::shutdown_pigpio()
+{
+    if (m_impl->pigpio_is_isitialized)
+        gpioTerminate();
 
-//     m_impl->pigpio_is_isitialized = false;
-// }
+    m_impl->pigpio_is_isitialized = false;
+}
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -253,6 +253,8 @@ bool PI_HAL::init_display_dispmanx()
 
 bool PI_HAL::init_display_sdl()
 {
+    //SDL_LogSetAllPriority(SDL_LOG_PRIORITY_VERBOSE);
+
 #ifdef USE_SDL
     SDL_Init(SDL_INIT_VIDEO);
 #ifdef USE_BOUBLE_BUFFER
@@ -265,14 +267,18 @@ bool PI_HAL::init_display_sdl()
     SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
     SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
     SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
-    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 0); 
+    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8); 
     SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0); 
 
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
     SDL_GL_SetAttribute(SDL_GL_SHARE_WITH_CURRENT_CONTEXT, 1); 
 
+    SDL_SetHintWithPriority(SDL_HINT_VIDEO_DOUBLE_BUFFER, "1", SDL_HINT_OVERRIDE);
+    //SDL_SetHintWithPriority(SDL_HINT_RENDER_VSYNC, "0", SDL_HINT_OVERRIDE);
+    
+
     int driver_count = SDL_GetNumVideoDrivers();
     LOGI("Drivers: {}", driver_count);
     for (int i = 0; i < driver_count; i++)
@@ -290,9 +296,9 @@ bool PI_HAL::init_display_sdl()
 
     // Create an application window with the following settings:
     m_impl->window = SDL_CreateWindow(
-        "An SDL2 window",                  // window title
-        SDL_WINDOWPOS_UNDEFINED,           // initial x position
-        SDL_WINDOWPOS_UNDEFINED,           // initial y position
+        "ESP32 FPV",                  // window title
+        0,           // initial x position
+        0,           // initial y position
         m_impl->width,                               // width, in pixels
         m_impl->height,                               // height, in pixels
         SDL_WINDOW_FULLSCREEN | 
@@ -430,6 +436,8 @@ bool PI_HAL::update_display()
     }
 
     SDL_GL_SwapWindow(m_impl->window);
+    //SDL_GL_SwapWindow(m_impl->window);
+    //SDL_GL_SwapWindow(m_impl->window);
     //glFlush();
 
     ImGui_ImplSDL2_NewFrame(m_impl->window);
@@ -580,11 +588,11 @@ bool PI_HAL::init()
     bcm_host_init();
 #endif
 
-    // if (!init_pigpio())
-    // {
-    //     LOGE("Cannot initialize pigpio");
-    //     return false;
-    // }
+    if (!init_pigpio())
+    {
+        LOGE("Cannot initialize pigpio");
+        return false;
+    }
     if (!init_display())
     {
         LOGE("Cannot initialize display");
@@ -614,7 +622,7 @@ void PI_HAL::shutdown()
 {
     ImGui_ImplOpenGL3_Shutdown();
 
-    //shutdown_pigpio();
+    shutdown_pigpio();
     shutdown_ts();
     shutdown_display();
 }