readmes and gps changes

README.md

@@ -1,5 +1,22 @@
 # SkyLok
 
+Pi Zero W 2 captures frames, runs a motion shader, sends diffs over LoRa.
+
+- `camera_example/`   — libcamera + libjpeg-turbo, streams MJPEG over TCP. Works.
+- `shader_example/`   — offscreen GL motion diff between two frames. Works on desktop.
+- `math_example/`     — pixel → 3D vertex projection (depth map to OBJ mesh).
+- `chip_test_example/` — LR1121 LoRa + ICM-20948 IMU + u-blox GPS drivers/tests.
+- `main.cpp`          — prototype that wires camera + shader + TCP together.
+
+References:
 - https://www.youtube.com/watch?v=zFiubdrJqqI
-- Client: libcamera::DirectLowResVid -> EGL::MotionShader -> MATH::Vortexes -> SPI/RadioHead::LoRa -> Server
+- https://github.com/ConsistentlyInconsistentYT/Pixeltovoxelprojector/
-- Server: eats all incoming and cooks
+
+## Build main.cpp
+
+```sh
+g++ main.cpp -o main \
+  $(pkg-config --cflags --libs libcamera libevent) \
+  -levent -levent_pthreads -lpthread \
+  -lturbojpeg -lglfw -lGLEW -lGL -lEGL -lGLESv2
+```

camera_example/README.md

@@ -1,27 +1,29 @@
 # camera_example
 
-libcamera viewfinder (XRGB8888) -> libjpeg-turbo -> TCP. One client at a time.
+libcamera viewfinder (XRGB8888) → libjpeg-turbo → TCP. One client at a time.
 
-Wire format: `[uint32 BE jpeg_size][jpeg_bytes]` repeating.
+Wire format: `[uint32 BE size][jpeg_bytes]` repeating.
 
-Knobs are constants at the top of `camera.cpp` (fps, quality, AF mode, lens
+Knobs (fps, quality, AF, lens, port, resolution) are `constexpr` at the top of `camera.cpp`.
-position, port, resolution).
 
 ## Build on the Pi
 
+```sh
 apt install g++ pkg-config libcamera-dev libevent-dev libjpeg-turbo8-dev
 make
-
+```
-## Cross-build (x86 -> armv6l) on a Nix host
-
-    nix build
-
-The resulting binary links against `/nix/store`, so it only runs on a Pi that
-has those libs available (i.e. nix installed). For a vanilla Pi OS target,
-use the Makefile on the device, or `./deploy.sh user@host` to rsync+build.
 
 ## Receive
 
-Any TCP client that reads the framed JPEGs. Quick check:
+```sh
-
 nc <pi-ip> 5000 | ffplay -f mjpeg -
+```
+
+## Cross-build (Nix, x86 → armv6l)
+
+```sh
+nix build
+```
+
+Binary links against `/nix/store` so it only runs on a Pi with Nix installed.
+For plain Pi OS: use `make` on the device, or `./deploy.sh user@host` to rsync+build.

chip_test_example/README.md

@@ -0,0 +1,120 @@
+# chip_test_example
+
+Tests for LR1121 LoRa, ICM-20948 IMU, u-blox GPS on Raspberry Pi Zero W 2.
+Header-only drivers, kernel ioctls, no external libs.
+
+---
+
+## Wiring
+
+### LR1121 (SPI0)
+
+| Module | Pi GPIO | Pi pin |
+|--------|---------|--------|
+| SCK    | GPIO11  | 23 |
+| MOSI   | GPIO10  | 19 |
+| MISO   | GPIO9   | 21 |
+| NSS    | GPIO8   | 24 |
+| BUSY   | GPIO24  | 18 |
+| NRESET | GPIO25  | 22 |
+| DIO9   | GPIO4   | 7  |
+| DIO8   | GPIO23  | 16 |
+
+Enable: `sudo raspi-config` → Interfaces → SPI → Yes → reboot
+
+### ICM-20948 (I2C1)
+
+| Module | Pi GPIO | Pi pin |
+|--------|---------|--------|
+| SDA    | GPIO2   | 3 |
+| SCL    | GPIO3   | 5 |
+| AD0    | GND → addr 0x68 / VCC → addr 0x69 |
+
+Enable: `sudo raspi-config` → Interfaces → I2C → Yes → reboot
+
+### u-blox GPS (UART0)
+
+| Module | Pi GPIO | Pi pin |
+|--------|---------|--------|
+| TX     | GPIO15  | 10 |
+| RX     | GPIO14  | 8  |
+
+Enable: `sudo raspi-config` → Interfaces → Serial Port → login shell: No, hardware: Yes → reboot
+
+---
+
+## Build
+
+```sh
+sudo apt install g++ make
+make
+```
+
+Run verbose first so you see exactly where it fails:
+
+```sh
+sudo ./lora_rx -v --433
+sudo ./imu_test -v
+./gps_test -v
+```
+
+---
+
+## LoRa debug
+
+```sh
+ls /dev/spidev0.0         # SPI on?
+sudo ./lora_rx -v --433   # step labels show exactly which command hangs
+```
+
+If it hangs at `Calibrate` — that's a TCXO config issue. Try in order:
+
+```sh
+sudo ./lora_rx -v --433 --tcxo-none   # skip TCXO entirely (crystal mode)
+sudo ./lora_rx -v --433 --tcxo-27     # TCXO 2.7V
+sudo ./lora_rx -v --433 --tcxo-33     # TCXO 3.3V (default)
+```
+
+The one that gets past "Calibrate done" is your module's config.
+Use the same TCXO flag on TX and RX.
+
+If using the 2.4 GHz antenna instead:
+
+```sh
+sudo ./lora_rx -v --24
+sudo ./lora_tx -v --24
+```
+
+---
+
+## IMU debug
+
+```sh
+sudo i2cdetect -y 1     # 0x68 or 0x69 must show
+sudo ./imu_test -v      # auto-detects both addresses
+sudo ./imu_test -v -r   # raw 16-bit values
+```
+
+Nothing on i2cdetect: I2C not enabled, wrong wiring, or no pull-ups on SDA/SCL.
+
+---
+
+## GPS debug
+
+```sh
+ls -la /dev/serial0
+stty -F /dev/serial0 38400 raw && cat /dev/serial0   # raw NMEA bytes
+./gps_test -v -a                                      # all sentences
+./gps_test -b 9600                                    # try different baud
+```
+
+---
+
+## TCXO voltage reference
+
+| Flag | Value | Voltage |
+|------|-------|---------|
+| `--tcxo-none` | 0xFF | no TCXO (crystal) |
+| `--tcxo-27`   | 0x05 | 2.7V |
+| `--tcxo-33`   | 0x07 | 3.3V |
+| `--tcxo-v N`  | 0x00–0x07 | raw byte |

chip_test_example/gps.hpp

@@ -1,19 +1,21 @@
 // gps.hpp — u-blox NMEA GPS reader over UART
 // No external libs; uses POSIX termios + read().
 //
-// Hardware pins (THE TRUTH):
+// Hardware (THE TRUTH):
-//   GPIO14/TXD0 → UBLOX_TX line  (/dev/serial0)
+//   GPIO14/TXD0 → UBLOX_TX  (/dev/serial0)
-//   GPIO15/RXD0 → UBLOX_RX line
+//   GPIO15/RXD0 → UBLOX_RX
-//   Default baud: 9600
+//   Default baud: 38400 (factory default on this module)
 //
 // Enable UART: sudo raspi-config → Interfaces → Serial Port
 //   "login shell over serial" = No, "serial port hardware" = Yes
+// Then reboot.  Check: ls -la /dev/serial0
 #pragma once
 
-#include <cstdio>
+#include <chrono>
-#include <cstring>
 #include <cmath>
+#include <cstdio>
 #include <cstdlib>
+#include <cstring>
 
 #include <fcntl.h>
 #include <termios.h>
@@ -30,30 +32,57 @@ struct Fix {
     char   date[7]{};    // DDMMYY
 };
 
+struct Config {
+    const char *dev  = "/dev/serial0";
+    int         baud = 38400;  // confirmed working baud for this module
+    bool        verbose = false;
+};
+
 class Reader {
 public:
-    bool begin(const char *dev = "/dev/serial0", int baud = 9600);
+    bool begin(const Config &cfg);
+    bool begin(const char *dev = "/dev/serial0", int baud = 38400);
     void end();
 
-    // Read one NMEA sentence into buf (null-terminated). Returns false on error.
+    // Read one NMEA sentence (null-terminated, includes '\n').
-    bool readLine(char *buf, size_t cap);
+    // timeout_ms: 0 = block forever, >0 = return false after timeout.
+    bool readLine(char *buf, size_t cap, uint32_t timeout_ms = 0);
 
-    // Parse $GPRMC or $GNRMC from a sentence. Returns false if sentence is
+    // Parse $GPRMC or $GNRMC. Returns false if wrong sentence type or fix void.
-    // not RMC or position is invalid.
     static bool parseRmc(const char *sentence, Fix &fix);
 
+    // Verify NMEA checksum: XOR of bytes between '$' and '*'.
+    static bool verifyChecksum(const char *sentence);
+
 private:
     int  fd_      = -1;
+    bool verbose_ = false;
 };
 
+// ---- Implementation ---------------------------------------------------------
+
+inline bool Reader::begin(const Config &c)
+{
+    verbose_ = c.verbose;
+    return begin(c.dev, c.baud);
+}
+
 inline bool Reader::begin(const char *dev, int baud)
 {
     fd_ = ::open(dev, O_RDWR | O_NOCTTY | O_NDELAY);
-    if (fd_ < 0) return false;
+    if (fd_ < 0) {
-    ::fcntl(fd_, F_SETFL, 0); // blocking
+        if (verbose_)
+            std::fprintf(stderr, "[gps] cannot open %s: %m\n", dev);
+        return false;
+    }
+    ::fcntl(fd_, F_SETFL, 0); // blocking reads
 
     termios t{};
-    if (tcgetattr(fd_, &t) < 0) return false;
+    if (tcgetattr(fd_, &t) < 0) {
+        if (verbose_) std::fprintf(stderr, "[gps] tcgetattr failed: %m\n");
+        ::close(fd_); fd_ = -1;
+        return false;
+    }
 
     speed_t spd;
     switch (baud) {
@@ -62,14 +91,26 @@ inline bool Reader::begin(const char *dev, int baud)
         case 19200:  spd = B19200;  break;
         case 38400:  spd = B38400;  break;
         case 57600:  spd = B57600;  break;
-        default:    spd = B9600;
+        case 115200: spd = B115200; break;
+        default:
+            if (verbose_)
+                std::fprintf(stderr, "[gps] unknown baud %d, defaulting to 38400\n", baud);
+            spd = B38400;
     }
     cfsetispeed(&t, spd);
     cfsetospeed(&t, spd);
     cfmakeraw(&t);
     t.c_cc[VMIN]  = 1;
     t.c_cc[VTIME] = 0;
-    tcsetattr(fd_, TCSANOW, &t);
+    if (tcsetattr(fd_, TCSANOW, &t) < 0) {
+        if (verbose_) std::fprintf(stderr, "[gps] tcsetattr failed: %m\n");
+        ::close(fd_); fd_ = -1;
+        return false;
+    }
+    tcflush(fd_, TCIOFLUSH);
+
+    if (verbose_)
+        std::fprintf(stderr, "[gps] opened %s at %d baud\n", dev, baud);
     return true;
 }
 
@@ -78,18 +119,37 @@ inline void Reader::end()
     if (fd_ >= 0) { ::close(fd_); fd_ = -1; }
 }
 
-inline bool Reader::readLine(char *buf, size_t cap)
+inline bool Reader::readLine(char *buf, size_t cap, uint32_t timeout_ms)
 {
+    using clock = std::chrono::steady_clock;
+    auto deadline = clock::now() + std::chrono::milliseconds(timeout_ms);
+
+    auto timed_read = [&](char &c) -> bool {
+        if (timeout_ms == 0) {
+            return ::read(fd_, &c, 1) == 1;
+        }
+        // Non-blocking check with timeout.
+        while (true) {
+            ssize_t r = ::read(fd_, &c, 1);
+            if (r == 1) return true;
+            if (clock::now() >= deadline) return false;
+            // Brief yield to avoid spinning.
+            struct timespec ts = { 0, 1'000'000 }; // 1 ms
+            nanosleep(&ts, nullptr);
+        }
+    };
+
     size_t n = 0;
     char   c;
-    // Wait for '$' (start of NMEA sentence)
+
+    // Wait for '$' (start of sentence).
     do {
-        if (::read(fd_, &c, 1) != 1) return false;
+        if (!timed_read(c)) return false;
     } while (c != '$');
     buf[n++] = '$';
 
     while (n < cap - 1) {
-        if (::read(fd_, &c, 1) != 1) return false;
+        if (!timed_read(c)) return false;
         buf[n++] = c;
         if (c == '\n') break;
     }
@@ -97,23 +157,38 @@ inline bool Reader::readLine(char *buf, size_t cap)
     return true;
 }
 
-// Parse $GPRMC or $GNRMC
+inline bool Reader::verifyChecksum(const char *sentence)
-// Format: $GNRMC,HHMMSS.ss,A,DDMM.MMMM,N,DDDMM.MMMM,E,spd,crs,DDMMYY,...
+{
+    // Checksum is XOR of all bytes between '$' (exclusive) and '*' (exclusive).
+    const char *p = sentence;
+    if (*p == '$') ++p;
+
+    uint8_t calc = 0;
+    while (*p && *p != '*') calc ^= (uint8_t)*p++;
+    if (*p != '*') return false; // no checksum present
+
+    unsigned int given = 0;
+    if (std::sscanf(p + 1, "%02X", &given) != 1) return false;
+    return (uint8_t)given == calc;
+}
+
+// Parse $GPRMC or $GNRMC.
+// Format: $GNRMC,HHMMSS.ss,A,DDMM.MMMM,N,DDDMM.MMMM,E,spd,crs,DDMMYY,...*CS
 inline bool Reader::parseRmc(const char *sentence, Fix &fix)
 {
     if (!sentence) return false;
-
-    // Check sentence type
     if (std::strncmp(sentence, "$GPRMC", 6) != 0 &&
         std::strncmp(sentence, "$GNRMC", 6) != 0)
         return false;
 
-    // Make a mutable copy
+    // Make a mutable copy for tokenization (strip the *CS checksum tail).
     char buf[128];
     std::strncpy(buf, sentence, sizeof(buf) - 1);
     buf[sizeof(buf) - 1] = '\0';
+    // Terminate at '*' so strtok doesn't swallow the checksum as a field.
+    char *star = std::strchr(buf, '*');
+    if (star) *star = '\0';
 
-    // Tokenize on commas
     const char *fields[13]{};
     int         nf = 0;
     char       *p  = buf;
@@ -126,31 +201,22 @@ inline bool Reader::parseRmc(const char *sentence, Fix &fix)
     }
     if (nf < 10) return false;
 
-    // field[2] = status ('A'=valid, 'V'=void)
     if (fields[2][0] != 'A') { fix.valid = false; return false; }
 
-    // field[1] = time
     std::strncpy(fix.time, fields[1], sizeof(fix.time) - 1);
 
-    // field[3] = lat DDMM.MMMM, field[4] = N/S
     double raw_lat = std::atof(fields[3]);
     int    lat_deg = (int)(raw_lat / 100.0);
-    double lat_min = raw_lat - lat_deg * 100.0;
+    fix.lat = lat_deg + (raw_lat - lat_deg * 100.0) / 60.0;
-    fix.lat = lat_deg + lat_min / 60.0;
     if (fields[4][0] == 'S') fix.lat = -fix.lat;
 
-    // field[5] = lon DDDMM.MMMM, field[6] = E/W
     double raw_lon = std::atof(fields[5]);
     int    lon_deg = (int)(raw_lon / 100.0);
-    double lon_min = raw_lon - lon_deg * 100.0;
+    fix.lon = lon_deg + (raw_lon - lon_deg * 100.0) / 60.0;
-    fix.lon = lon_deg + lon_min / 60.0;
     if (fields[6][0] == 'W') fix.lon = -fix.lon;
 
     fix.speed_knots = (float)std::atof(fields[7]);
-
-    // field[9] = date DDMMYY
     std::strncpy(fix.date, fields[9], sizeof(fix.date) - 1);
-
     fix.valid = true;
     return true;
 }

chip_test_example/gps_test.cpp

@@ -1,39 +1,82 @@
+// gps_test.cpp — u-blox GPS NMEA test
+// Usage: ./gps_test [-v] [-a] [-b BAUD]
+//   -v        verbose init debug
+//   -a        print ALL NMEA sentences (not just RMC)
+//   -b BAUD   set baud rate (default 38400)
+//
+// Enable UART: sudo raspi-config → Interfaces → Serial Port
+//   login shell: No, serial hardware: Yes → reboot
+// Check: ls -la /dev/serial0
+// Sniff raw bytes to confirm module is transmitting:
+//   stty -F /dev/serial0 38400 raw && cat /dev/serial0
 #include <cstdio>
-
+#include <cstdlib>
+#include <cstring>
 #include "gps.hpp"
 
-int main()
+int main(int argc, char **argv)
 {
-    gps::Reader reader;
+    gps::Config cfg;
+    cfg.verbose = false;
+    bool show_all = false;
 
-    if (!reader.begin()) {
+    for (int i = 1; i < argc; ++i) {
-        std::fprintf(stderr, "gps open failed\n"
+        if (std::strcmp(argv[i], "-v") == 0) {
-            "  check /dev/serial0 (UART)\n"
+            cfg.verbose = true;
-            "  enable serial: sudo raspi-config -> Interfaces -> Serial Port\n"
+        } else if (std::strcmp(argv[i], "-a") == 0) {
-            "    login shell = No, hardware = Yes\n");
+            show_all = true;
+        } else if (std::strcmp(argv[i], "-b") == 0 && i + 1 < argc) {
+            cfg.baud = std::atoi(argv[++i]);
+        }
+    }
+
+    std::printf("gps_test: %s @%d baud%s%s\n",
+                cfg.dev, cfg.baud,
+                cfg.verbose ? " [verbose]" : "",
+                show_all    ? " [all sentences]" : "");
+
+    gps::Reader gps;
+    if (!gps.begin(cfg)) {
+        std::fprintf(stderr, "ERROR: cannot open %s\n"
+                             "  Check: UART enabled? (sudo raspi-config)\n"
+                             "  Check: ls -la /dev/serial0\n"
+                             "  Check: wiring TX=GPIO14 RX=GPIO15\n", cfg.dev);
         return 1;
     }
-    std::fprintf(stderr, "gps reading /dev/serial0 at 9600...\n");
+    std::printf("UART open — waiting for NMEA (Ctrl+C to stop)\n\n");
 
     char line[128];
-    gps::Fix fix;
+    int  fixes = 0;
     for (;;) {
-        if (!reader.readLine(line, sizeof(line))) {
+        // 2s per sentence timeout — if nothing arrives, likely wiring or baud mismatch
-            std::fprintf(stderr, "uart read error\n");
+        if (!gps.readLine(line, sizeof(line), 2000)) {
-            break;
+            std::printf("  [timeout: no NMEA for 2s — check wiring and baud rate]\n");
-        }
-        if (!gps::Reader::parseRmc(line, fix)) {
-            // Not an RMC sentence or no fix — print raw line for debug
-            // std::fprintf(stderr, "raw: %s", line);
             continue;
         }
+
+        // Checksum validation
+        bool cs_ok = gps::Reader::verifyChecksum(line);
+        if (cfg.verbose && !cs_ok)
+            std::printf("  [bad checksum] %s", line);
+
+        if (show_all) {
+            std::printf("%s", line);
+            continue;
+        }
+
+        gps::Fix fix;
+        if (gps::Reader::parseRmc(line, fix)) {
             if (fix.valid) {
-            std::fprintf(stderr, "fix  lat=%+.6f  lon=%+.6f  spd=%.1f kn  "
+                std::printf("[%4d] %s %s | lat=%+.6f lon=%+.6f spd=%.1fkn%s\n",
-                         "time=%s  date=%s\n",
+                            ++fixes, fix.date, fix.time,
                             fix.lat, fix.lon, fix.speed_knots,
-                         fix.time, fix.date);
+                            cs_ok ? "" : " [bad cs]");
             } else {
-            std::fprintf(stderr, "no fix\n");
+                std::printf("       no fix (GPRMC/GNRMC status=V)\n");
             }
         }
     }
+
+    gps.end();
+    return 0;
+}

math_example/README.md

@@ -0,0 +1,38 @@
+# math_example
+
+Basic pixel → 3D vertex projection. Each pixel's brightness is used as depth in a
+pinhole back-projection:
+
+```
+x = (u - cx) / fx * depth
+y = (v - cy) / fy * depth
+z = depth
+```
+
+Output is a triangulated OBJ mesh. Bright pixels project far from the camera,
+dark pixels stay close. Gives a height-map-like 3D surface from any image.
+
+## Build
+
+```sh
+make
+```
+
+Needs only the C++ stdlib and `stb_image` from `../shader_example/`.
+
+## Run
+
+```sh
+./math                                   # 128x128 sine-wave test pattern
+./math ../shader_example/frame1.jpg      # load an image
+./math ../shader_example/frame1.jpg 2   # step=2 (denser mesh)
+./math ../shader_example/frame1.jpg 4 90  # step=4, FOV 90°
+```
+
+Output: `out.obj` — open in Blender (`File → Import → Wavefront`) or MeshLab.
+
+## What it's for
+
+This is the math layer that sits between the camera and the LoRa transmitter.
+Instead of sending raw pixels, you project them to vertices, run motion detection
+in that 3D space, and transmit only the diff vertices over LoRa.

shader_example/README.md

@@ -0,0 +1,10 @@
+# shader_example
+
+Loads `frame1.jpg` and `frame2.jpg`, runs `motion.frag` (per-pixel `|A - B|`)
+on the GPU, writes result to `frameO.jpg`. Desktop GL 3.3, GLFW + GLEW.
+
+```sh
+g++ shader.cpp -o shader -lglfw -lGLEW -lGL && ./shader
+```
+
+`stb_image.hpp` and `stb_image_write.hpp` are vendored in this folder.