[bmix]

Old thread, I know, but makes sense to expand on it...

The reMarkable does not connect as USB disk (or MTP) device. Here is what I know so far:

• Remarkable company supports only transfer of books via their cloud app. You "import" files from your desktop, it sends it to the cloud, optimizes it to the device spec (?) and pushes it to your device.
  
• The only alternative to the cloud is SSH. When the device gets connected to a computer via the USB cable, the reMarkable becomes a USB network device, which accepts SSH connections (by root only). Now data can be transfered via SCP/SFTP.
  
• However, you can not simply drag and drop to the filesystem, since they use a more "database" like approach (all books get additional metadata files and all ends up in a single, mostly flat, directory structure). Here is how two ePub files end up on the filesystem (note also, that the filenames get replaced with UUIDs):
  
  

  24.11.2020  08:18    <DIR>          4cb0c193-f468-456d-8eda-e41170e7e7f3
  24.11.2020  12:01            31.801 4cb0c193-f468-456d-8eda-e41170e7e7f3.content
  24.11.2020  06:21         2.262.475 4cb0c193-f468-456d-8eda-e41170e7e7f3.epub
  24.11.2020  12:01               417 4cb0c193-f468-456d-8eda-e41170e7e7f3.metadata
  24.11.2020  12:01             3.918 4cb0c193-f468-456d-8eda-e41170e7e7f3.pagedata
  24.11.2020  08:18         4.236.278 4cb0c193-f468-456d-8eda-e41170e7e7f3.pdf
  24.11.2020  08:18    <DIR>          4cb0c193-f468-456d-8eda-e41170e7e7f3.thumbnails
  24.11.2020  08:11    <DIR>          72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c
  24.11.2020  12:01            50.281 72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.content
  25.11.2020  11:32           706.863 72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.epub
  24.11.2020  12:01               352 72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.metadata
  24.11.2020  12:01             6.000 72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.pagedata
  24.11.2020  06:28         3.252.916 72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.pdf
  24.11.2020  08:05    <DIR>          72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.thumbnails
                10 Datei(en),     10.551.301 Bytes
  
  C:\Users\bmix\Desktop\TMP\reMarkable>du -h .
  0       ./4cb0c193-f468-456d-8eda-e41170e7e7f3
  8.0K    ./4cb0c193-f468-456d-8eda-e41170e7e7f3.thumbnails
  77K     ./72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c
  452K    ./72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.thumbnails
  11M     .

  In the end one ends up with a hierarchy like this:
  
  

  4cb0c193-f468-456d-8eda-e41170e7e7f3/
  4cb0c193-f468-456d-8eda-e41170e7e7f3.thumbnails/
    39250e3a-3f29-445b-910e-bf41401b2d3e.jpg                         7 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c/
    c83514a7-ec85-4db2-a928-c4695efa7eba.rm                         71 KB
    c83514a7-ec85-4db2-a928-c4695efa7eba-metadata.json               1 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.thumbnails/
    1d119952-3512-40d6-82ae-c7636ab8373b.jpg                        32 KB
    2d156753-e6cb-4660-8123-b1fe484aa268.jpg                        29 KB
    6e4c4334-27be-466d-a0e9-c0fed40bcf6e.jpg                        12 KB
    9ab6a578-a8fb-4281-85c4-2ed4b80e7f8c.jpg                         7 KB
    67fd7b3b-8dc6-4082-b06a-b1c0a5620b73.jpg                        31 KB
    97d9e33f-af10-490a-b569-177963812739.jpg                        32 KB
    880eb47f-123e-4f0d-a40d-de3b70733465.jpg                        32 KB
    1726c51d-c890-4a8c-87d5-39a9637e62d5.jpg                        31 KB
    026927cd-6a8a-40f5-bb1b-c539b075d805.jpg                        31 KB
    250835cc-5e68-4884-b384-a9b4cd60dbf7.jpg                        31 KB
    b330d87c-0eed-49a2-be64-9ab49dbf8950.jpg                         5 KB
    c83514a7-ec85-4db2-a928-c4695efa7eba.jpg                        30 KB
    d055bfb4-f22a-4b48-b43f-8b2e75e0d43b.jpg                        32 KB
    d447c247-7fd9-4272-9167-812280ed0c6a.jpg                        32 KB
    dce72072-93c8-4f91-b469-c7411d07c4c5.jpg                        32 KB
    e250db1a-7b19-4ff9-bc06-78e98630f4e1.jpg                        32 KB
  4cb0c193-f468-456d-8eda-e41170e7e7f3.content                      32 KB
  4cb0c193-f468-456d-8eda-e41170e7e7f3.epub                      2.210 KB
  4cb0c193-f468-456d-8eda-e41170e7e7f3.metadata                      1 KB
  4cb0c193-f468-456d-8eda-e41170e7e7f3.pagedata                      4 KB
  4cb0c193-f468-456d-8eda-e41170e7e7f3.pdf                       4.137 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.content                      50 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.epub                        691 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.metadata                      1 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.pagedata                      6 KB
  72d8bbdd-cbe2-44b2-8b6d-1dfdb4587c5c.pdf                       3.177 KB

  The thumbnail files seem to contain thumbnails for those pages, which have already been opened.
  
• Remarkable states support for PDF and ePub, but ePub support is not real. What happens, instead, is, that the ePub gets converted to PDF and then the ePub and the PDF get pushed to your device. The reader can not display the ePub, but only the PDF. ePub conversion is slow on the device.

An output device for Calibre would need to implement

• SFTP transfer with the device
  
• handling of the filesystem layout and creation of the metadata and thumbnail files
  
• keep a mapping between the device's "library" and Calibre's
  
• as bonus: do the conversion of ePub into PDF with Calibe before transfer

That's all I know for now. There is a whole bunch of utilities, that try to make life easier at github.com/reHackable/awesome-reMarkable, but no Calibre device, so far.