text: enum {
    PORT_A,
    PORT_B,
    PORT_C,
    PORT_D,
    PORT_E,
    PORT_F,
    PORT_G,
    PORT_H,
    PORT_I,
    PORT_J,
  };
  
  enum {
    AF_FN_TIM,
    AF_FN_I2C,
    AF_FN_USART,
    AF_FN_UART = AF_FN_USART,
    AF_FN_SPI
  };
  
  enum {
    AF_PIN_TYPE_TIM_CH1 = 0,
    AF_PIN_TYPE_TIM_CH2,
    AF_PIN_TYPE_TIM_CH3,
    AF_PIN_TYPE_TIM_CH4,
    AF_PIN_TYPE_TIM_CH1N,
    AF_PIN_TYPE_TIM_CH2N,
    AF_PIN_TYPE_TIM_CH3N,
    AF_PIN_TYPE_TIM_CH1_ETR,
    AF_PIN_TYPE_TIM_ETR,
    AF_PIN_TYPE_TIM_BKIN,
  
    AF_PIN_TYPE_I2C_SDA = 0,
    AF_PIN_TYPE_I2C_SCL,
  
    AF_PIN_TYPE_USART_TX = 0,
    AF_PIN_TYPE_USART_RX,
    AF_PIN_TYPE_USART_CTS,
    AF_PIN_TYPE_USART_RTS,
    AF_PIN_TYPE_USART_CK,
    AF_PIN_TYPE_UART_TX  = AF_PIN_TYPE_USART_TX,
    AF_PIN_TYPE_UART_RX  = AF_PIN_TYPE_USART_RX,
    AF_PIN_TYPE_UART_CTS = AF_PIN_TYPE_USART_CTS,
    AF_PIN_TYPE_UART_RTS = AF_PIN_TYPE_USART_RTS,
  
    AF_PIN_TYPE_SPI_MOSI = 0,
    AF_PIN_TYPE_SPI_MISO,
    AF_PIN_TYPE_SPI_SCK,
    AF_PIN_TYPE_SPI_NSS,
  };
  
  enum {
    PIN_ADC1  = (1 << 0),
    PIN_ADC2  = (1 << 1),
    PIN_ADC3  = (1 << 2),
  };
  
  typedef struct {
    mp_obj_base_t base;
    uint8_t idx;
    uint8_t fn;
    uint8_t unit;
    uint8_t type;
  
    union {
      void          *reg;
      TIM_TypeDef   *TIM;
      I2C_TypeDef   *I2C;
      USART_TypeDef *USART;
      USART_TypeDef *UART;
      SPI_TypeDef   *SPI;
    };
  } pin_af_obj_t;
  
  typedef struct {
    mp_obj_base_t base;
    const char *name;
    uint16_t port   : 4;
    uint16_t pin    : 4;
    uint16_t num_af : 4;
    uint16_t adc_channel : 4;
    uint16_t adc_num  : 3;  // 1 bit per ADC
    uint16_t pin_mask;
    GPIO_TypeDef *gpio;
    const pin_af_obj_t *af;
  } pin_obj_t;
  
  extern const mp_obj_type_t pin_type;
  extern const mp_obj_type_t pin_af_type;
  
  typedef struct {
    const char *name;
    const pin_obj_t *pin;
  } pin_named_pin_t;
  
  extern const pin_named_pin_t pin_board_pins[];
  extern const pin_named_pin_t pin_cpu_pins[];
  
  //extern pin_map_obj_t pin_map_obj;
  
  typedef struct {
      mp_obj_base_t base;
      qstr name;
      const pin_named_pin_t *named_pins;
  } pin_named_pins_obj_t;
  
  extern const pin_named_pins_obj_t pin_board_pins_obj;
  extern const pin_named_pins_obj_t pin_cpu_pins_obj;
  
  void pin_init(void);
  const pin_obj_t *pin_find(mp_obj_t user_obj);
  const pin_obj_t *pin_find_named_pin(const pin_named_pin_t *pins, const char *name);
  const pin_af_obj_t *pin_find_af(const pin_obj_t *pin, uint8_t fn, uint8_t unit, uint8_t pin_type);
  