fixup examples based on default pin #define-s and also support them being undefined

dma/channel_irq/channel_irq.c

@@ -52,6 +52,9 @@ void dma_handler() {
 }
 
 int main() {
+#ifndef PICO_DEFAULT_LED_PIN
+#warning dma/channel_irq example requires a board with a regular LED
+#else
     // Set up a PIO state machine to serialise our bits
     uint offset = pio_add_program(pio0, &pio_serialiser_program);
     pio_serialiser_program_init(pio0, 0, offset, PICO_DEFAULT_LED_PIN, PIO_SERIAL_CLKDIV);
@@ -87,5 +90,5 @@ int main() {
     // time to sit and think about its early retirement -- maybe open a bakery?
     while (true)
         tight_loop_contents();
-
+#endif
 }

dma/control_blocks/control_blocks.c

@@ -47,6 +47,9 @@ const struct {uint32_t len; const char *data;} control_blocks[] = {
 };
 
 int main() {
+#ifndef uart_default
+#warning dma/control_blocks example requires a UART
+#else
     stdio_init_all();
     puts("DMA control block example:");
 
@@ -81,7 +84,7 @@ int main() {
 
     c = dma_channel_get_default_config(data_chan);
     channel_config_set_transfer_data_size(&c, DMA_SIZE_8);
-    channel_config_set_dreq(&c, DREQ_UART0_TX + 2 * PICO_DEFAULT_UART);
+    channel_config_set_dreq(&c, DREQ_UART0_TX + 2 * uart_get_index(uart_default));
     // Trigger ctrl_chan when data_chan completes
     channel_config_set_chain_to(&c, ctrl_chan);
     // Raise the IRQ flag when 0 is written to a trigger register (end of chain):
@@ -90,7 +93,7 @@ int main() {
     dma_channel_configure(
         data_chan,
         &c,
-        &(PICO_DEFAULT_UART ? uart1_hw : uart0_hw)->dr,
+        &uart_get_hw(uart_default)->dr,
         NULL,           // Initial read address and transfer count are unimportant;
         0,              // the control channel will reprogram them each time.
         false           // Don't start yet.
@@ -108,4 +111,5 @@ int main() {
     dma_hw->ints0 = 1u << data_chan;
 
     puts("DMA finished.");
+#endif
 }