pybricks.iodevices.I2CDevice: Limit write to reg to 32 bytes.

This is sufficient for most operations and more sensible for NXT. Larger amounts of data can still be written by prefxing the register in the user code.

Author: laurensvalk

pybricks/iodevices/pb_type_i2c_device.c

@@ -18,7 +18,6 @@
 
 #include <pybricks/util_mp/pb_kwarg_helper.h>
 #include <pybricks/util_mp/pb_obj_helper.h>
-
 #include <pybricks/util_pb/pb_error.h>
 
 // Object representing a pybricks.iodevices.I2CDevice instance.
@@ -262,8 +261,10 @@ static mp_obj_t write(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args
         return pb_type_i2c_device_start_operation(MP_OBJ_FROM_PTR(device), (const uint8_t *)user_data, user_len, 0, NULL);
     }
 
-    // Otherwise need to prefix write data with given register.
-    uint8_t write_data[256];
+    // Otherwise need to prefix write data with given register. We're limiting
+    // write data to 32 bytes in this case. To send more data, the user can
+    // use reg=None and prefix the address to the data themselves.
+    uint8_t write_data[33];
     if (user_len > MP_ARRAY_SIZE(write_data) - 1) {
         pb_assert(PBIO_ERROR_INVALID_ARG);
     }