Add UDP transmitter example (#306)

Co-authored-by: Andrew McDonnell <bugs@andrewmcdonnell.net>

README.md

@@ -122,6 +122,7 @@ App|Description
 [picow_tcp_client](pico_w/tcp_client)| A simple TCP client. You can run [python_test_tcp_server.py](pico_w/python_test_tcp/python_test_tcp_server.py) for it to connect to.
 [picow_tcp_server](pico_w/tcp_server)| A simple TCP server. You can use [python_test_tcp_client.py](pico_w/python_test_tcp/python_test_tcp_client.py) to connect to it.
 [picow_wifi_scan](pico_w/wifi_scan)| Scans for WiFi networks and prints the results.
+[picow_udp_beacon](pico_w/udp_beacon)| A simple UDP transmitter.
 
 #### FreeRTOS examples
 

pico_w/CMakeLists.txt

@@ -32,6 +32,7 @@ if (PICO_CYW43_SUPPORTED) # set by PICO_BOARD=pico_w
             add_subdirectory(tcp_client)
             add_subdirectory(tcp_server)
             add_subdirectory(freertos)
+            add_subdirectory(udp_beacon)
         endif()
     endif()
 endif()

pico_w/udp_beacon/CMakeLists.txt

@@ -0,0 +1,34 @@
+add_executable(picow_udp_beacon_background
+        picow_udp_beacon.c
+        )
+target_compile_definitions(picow_udp_beacon_background PRIVATE
+        WIFI_SSID=\"${WIFI_SSID}\"
+        WIFI_PASSWORD=\"${WIFI_PASSWORD}\"
+        )
+target_include_directories(picow_udp_beacon_background PRIVATE
+        ${CMAKE_CURRENT_LIST_DIR}
+        ${CMAKE_CURRENT_LIST_DIR}/.. # for our common lwipopts
+        )
+target_link_libraries(picow_udp_beacon_background
+        pico_cyw43_arch_lwip_threadsafe_background
+        pico_stdlib
+        )
+
+pico_add_extra_outputs(picow_udp_beacon_background)
+
+add_executable(picow_udp_beacon_poll
+        picow_udp_beacon.c
+        )
+target_compile_definitions(picow_udp_beacon_poll PRIVATE
+        WIFI_SSID=\"${WIFI_SSID}\"
+        WIFI_PASSWORD=\"${WIFI_PASSWORD}\"
+        )
+target_include_directories(picow_udp_beacon_poll PRIVATE
+        ${CMAKE_CURRENT_LIST_DIR}
+        ${CMAKE_CURRENT_LIST_DIR}/.. # for our common lwipopts
+        )
+target_link_libraries(picow_udp_beacon_poll
+        pico_cyw43_arch_lwip_poll
+        pico_stdlib
+        )
+pico_add_extra_outputs(picow_udp_beacon_poll)

pico_w/udp_beacon/lwipopts.h

@@ -0,0 +1,10 @@
+#ifndef _LWIPOPTS_H
+#define _LWIPOPTS_H
+
+// Generally you would define your own explicit list of lwIP options
+// (see https://www.nongnu.org/lwip/2_1_x/group__lwip__opts.html)
+//
+// This example uses a common include to avoid repetition
+#include "lwipopts_examples_common.h"
+
+#endif

pico_w/udp_beacon/picow_udp_beacon.c

@@ -0,0 +1,79 @@
+/**
+ * Copyright (c) 2022 Andrew McDonnell
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <string.h>
+#include <stdlib.h>
+
+#include "pico/stdlib.h"
+#include "pico/cyw43_arch.h"
+
+#include "lwip/pbuf.h"
+#include "lwip/udp.h"
+
+#define UDP_PORT 4444
+#define BEACON_MSG_LEN_MAX 127
+#define BEACON_TARGET "255.255.255.255"
+#define BEACON_INTERVAL_MS 1000
+
+void run_udp_beacon() {
+    struct udp_pcb* pcb = udp_new();
+
+    ip_addr_t addr;
+    ipaddr_aton(BEACON_TARGET, &addr);
+
+    int counter = 0;
+    while (true) {
+        struct pbuf *p = pbuf_alloc(PBUF_TRANSPORT, BEACON_MSG_LEN_MAX+1, PBUF_RAM);
+        char *req = (char *)p->payload;
+        memset(req, 0, BEACON_MSG_LEN_MAX+1);
+        snprintf(req, BEACON_MSG_LEN_MAX, "%d\n", counter);
+        err_t er = udp_sendto(pcb, p, &addr, UDP_PORT);
+        pbuf_free(p);
+        if (er != ERR_OK) {
+            printf("Failed to send UDP packet! error=%d", er);
+        } else {
+            printf("Sent packet %d\n", counter);
+            counter++;
+        }
+
+        // Note in practice for this simple UDP transmitter,
+        // the end result for both background and poll is the same
+
+#if PICO_CYW43_ARCH_POLL
+        // if you are using pico_cyw43_arch_poll, then you must poll periodically from your
+        // main loop (not from a timer) to check for WiFi driver or lwIP work that needs to be done.
+        cyw43_arch_poll();
+        sleep_ms(BEACON_INTERVAL_MS);
+#else
+        // if you are not using pico_cyw43_arch_poll, then WiFI driver and lwIP work
+        // is done via interrupt in the background. This sleep is just an example of some (blocking)
+        // work you might be doing.
+        sleep_ms(BEACON_INTERVAL_MS);
+#endif
+    }
+}
+
+int main() {
+    stdio_init_all();
+
+    if (cyw43_arch_init()) {
+        printf("failed to initialise\n");
+        return 1;
+    }
+
+    cyw43_arch_enable_sta_mode();
+
+    printf("Connecting to WiFi...\n");
+    if (cyw43_arch_wifi_connect_timeout_ms(WIFI_SSID, WIFI_PASSWORD, CYW43_AUTH_WPA2_AES_PSK, 30000)) {
+        printf("failed to connect.\n");
+        return 1;
+    } else {
+        printf("Connected.\n");
+    }
+    run_udp_beacon();
+    cyw43_arch_deinit();
+    return 0;
+}