Add some extra defines to platform_defs.h (#227)

Author: lurch

src/rp2040/hardware_regs/include/hardware/platform_defs.h

@@ -25,6 +25,11 @@
 #define NUM_PWM_SLICES _u(8)
 #define NUM_SPIN_LOCKS _u(32)
 #define NUM_UARTS _u(2)
+#define NUM_I2CS _u(2)
+#define NUM_SPIS _u(2)
+
+#define NUM_ADC_CHANNELS _u(5)
+
 #define NUM_BANK0_GPIOS _u(30)
 
 #define PIO_INSTRUCTION_COUNT _u(32)

src/rp2_common/hardware_adc/include/hardware/adc.h

@@ -84,7 +84,7 @@ static inline void adc_gpio_init(uint gpio) {
  * \param input Input to select.
  */
 static inline void adc_select_input(uint input) {
-    invalid_params_if(ADC, input > 4);
+    valid_params_if(ADC, input < NUM_ADC_CHANNELS);
     hw_write_masked(&adc_hw->cs, input << ADC_CS_AINSEL_LSB, ADC_CS_AINSEL_BITS);
 }