apparently cart save still use 512 block inside

README.md

@@ -93,7 +93,7 @@ The parameters supported by `--format` are
  - `max_dir`/`max_file`: the maximum number of directories/files. The default is `100`
  - `dir_buckets`/`file_buckets`: the bucket count of the hash table for directories/files. The default value is calculated from `max_dir`/`max_file` using the common algorithm games use.
  - `len`: only for save data archive. Limits the physical size in bytes of the save data file. The defualt is `524288` (512 KiB). For Card1 cartridge save, only `131072` (128 KiB), `524288` (512 KiB), and `1048576` (1 MiB) are allowed, are must match the cartidge chip type.
- - `block_len`: only for save data archive. The value can only be `512` or `4096`. The default is `512` for `--sdsave` and `--bare`, and `4096` for `--nandsave` and `--cart`.
+ - `block_len`: only for save data archive. The value can only be `512` or `4096`. The default is `512` for `--sdsave`, `--bare` and, `--cart`, and `4096` for `--nandsave`.
  - `duplicate_data`: only for save data archive. The value can only be `true` or `false`. The default is `true`
 
 If you want leave all parameters in default values, you can specify an empty option, e.g. `--format ""`

save3ds_fuse/src/main.rs

@@ -1459,7 +1459,7 @@ fn main_inner() -> Result<(), Box<dyn std::error::Error>> {
     } else if let Some(cart) = cart_path {
         if let Some(format_param) = format_param {
             println!("Formatting...");
-            let (param, len) = to_save_data_format_param(format_param, 4096)?;
+            let (param, len) = to_save_data_format_param(format_param, 512)?;
             resource.format_cart_save(&cart, &param, len)?;
             println!("Formatting done");
         }