ports/rp2: Make I2C bus ID arg optional and use default if not provided

Author: malcolm-sparkfun

ports/rp2/machine_i2c.c

@@ -97,7 +97,7 @@ static void machine_i2c_print(const mp_print_t *print, mp_obj_t self_in, mp_prin
 mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
     enum { ARG_id, ARG_freq, ARG_scl, ARG_sda, ARG_timeout };
     static const mp_arg_t allowed_args[] = {
-        { MP_QSTR_id, MP_ARG_REQUIRED | MP_ARG_OBJ },
+        { MP_QSTR_id,  MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
         { MP_QSTR_freq, MP_ARG_INT, {.u_int = DEFAULT_I2C_FREQ} },
         { MP_QSTR_scl, MICROPY_I2C_PINS_ARG_OPTS | MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
         { MP_QSTR_sda, MICROPY_I2C_PINS_ARG_OPTS | MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
@@ -108,8 +108,20 @@ mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
-    // Get I2C bus.
-    int i2c_id = mp_obj_get_int(args[ARG_id].u_obj);
+    // Bus ID - use the default I2C bus as default
+    #ifdef PICO_DEFAULT_I2C
+    int i2c_id = PICO_DEFAULT_I2C;
+    #else
+    // invalid value
+    int i2c_id = -1;
+    #endif
+
+    // User provide a value?
+    if (args[ARG_id].u_obj != mp_const_none){
+        i2c_id = mp_obj_get_int(args[ARG_id].u_obj);
+    }
+    
+    // Check if the I2C bus is valid
     if (i2c_id < 0 || i2c_id >= MP_ARRAY_SIZE(machine_i2c_obj)) {
         mp_raise_msg_varg(&mp_type_ValueError, MP_ERROR_TEXT("I2C(%d) doesn't exist"), i2c_id);
     }