Make the blink example work on Pico W (#507)

* Make the blink example work on Pico W

It seems to confuse people that the blink example doesn't work on PicoW.
To avoid further confusion, make it work, rather than build and silently
do nothing.

blink/CMakeLists.txt

@@ -1,10 +1,14 @@
 add_executable(blink
-        blink.c
-        )
+    blink.c
+    )
 
 # pull in common dependencies
 target_link_libraries(blink pico_stdlib)
 
+if (PICO_CYW43_SUPPORTED)
+    target_link_libraries(blink pico_cyw43_arch_none)
+endif()
+
 # create map/bin/hex file etc.
 pico_add_extra_outputs(blink)
 

blink/blink.c

@@ -6,18 +6,48 @@
 
 #include "pico/stdlib.h"
 
+// Pico W devices use a GPIO on the WIFI chip for the LED,
+// so when building for Pico W, CYW43_WL_GPIO_LED_PIN will be defined
+#ifdef CYW43_WL_GPIO_LED_PIN
+#include "pico/cyw43_arch.h"
+#endif
+
+#ifndef LED_DELAY_MS
+#define LED_DELAY_MS 250
+#endif
+
+// Perform initialisation
+int pico_led_init(void) {
+#if defined(PICO_DEFAULT_LED_PIN)
+    // A device like Pico that uses a GPIO for the LED will define PICO_DEFAULT_LED_PIN
+    // so we can use normal GPIO functionality to turn the led on and off
+    gpio_init(PICO_DEFAULT_LED_PIN);
+    gpio_set_dir(PICO_DEFAULT_LED_PIN, GPIO_OUT);
+    return PICO_OK;
+#elif defined(CYW43_WL_GPIO_LED_PIN)
+    // For Pico W devices we need to initialise the driver etc
+    return cyw43_arch_init();
+#endif
+}
+
+// Turn the led on or off
+void pico_set_led(bool led_on) {
+#if defined(PICO_DEFAULT_LED_PIN)
+    // Just set the GPIO on or off
+    gpio_put(PICO_DEFAULT_LED_PIN, led_on);
+#elif defined(CYW43_WL_GPIO_LED_PIN)
+    // Ask the wifi "driver" to set the GPIO on or off
+    cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, led_on);
+#endif
+}
+
 int main() {
-#ifndef PICO_DEFAULT_LED_PIN
-#warning blink example requires a board with a regular LED
-#else
-    const uint LED_PIN = PICO_DEFAULT_LED_PIN;
-    gpio_init(LED_PIN);
-    gpio_set_dir(LED_PIN, GPIO_OUT);
+    int rc = pico_led_init();
+    hard_assert(rc == PICO_OK);
     while (true) {
-        gpio_put(LED_PIN, 1);
-        sleep_ms(250);
-        gpio_put(LED_PIN, 0);
-        sleep_ms(250);
+        pico_set_led(true);
+        sleep_ms(LED_DELAY_MS);
+        pico_set_led(false);
+        sleep_ms(LED_DELAY_MS);
     }
-#endif
 }