more notes + WIP wireshark pictochat dissector (brokey)

1 files changed, 67 insertions, 2 deletions

diff --git a/docs/notes.md b/docs/notes.md
index 21eef78..657383e 100644
--- a/docs/notes.md
+++ b/docs/notes.md
@@ -81,16 +81,81 @@ sufficiently advanced local multiplayer emulation.
 
 source: <https://git.pipeframe.xyz/fork/melonDS>
 
-### Findings
-
 - melonDS @ Config > Wifi settings "Local multiplayer features do not use the same network protocols as online play"
 - comment @ src/Wifi.cpp:46 "multiplayer host TX sequence"
 - references to `RFTransfer_Type{2,3}` @ <https://www.problemkaputt.de/gbatek.htm#dswifirfchip>
 - nintendo ds ni-fi protocol @ <https://web.archive.org/web/20090202194241/http://masscat.afraid.org/ninds/proto_info.php>
 - melonDS emulates actual 802.11b frames
 - the protocol does not appear to be encrypted:
+
   ![](../assets/ws-no-encrypt.png)
+
   the string `lork` is visible as plain text in the hexdump (offset 0x0056), which appears to
   be some kind of 16-bit encoding of the username set on the emulator used to
   capture these packets
+- The messages are not sent as single packets. The nifi protocol appears to set
+  up a constant stream, and messages are sent across multiple frames.
+- PictoChat does not appear to send messages when you are in a chat room by
+  yourself, so local multiplayer / nifi emulation is required for capturing
+  message content
+
+### Message sizing/cropping
+
+- PictoChat automatically crops messages to the smallest height (at the fixed
+  intervals shown as notebook lines in the edit field on the bottom screen).
+  Message content can be on the line itself without causing the cropping
+  algorithm to 'allocate' more space; the allocation only happens if any of the
+  pixels on the line *below* the colored line are used. The method used to crop
+  the messages also ensures that the username label in the top left does not
+  obstruct or remove any content.
+
+  ![](../assets/pictochat-msg-height-1-4.png)
+  ![](../assets/pictochat-msg-height-5-draw.png)
+- Message content is likely only cropped when displaying
+
+  ![](../assets/pictochat-msg-crop.png)
+  ![](../assets/pictochat-msg-crop-lork2.png)
+
+  The above image was obtained after the following steps:
+  - Fill in the top row of the message with the black pen, ensuring the entire
+    notebook line is colored in as well
+  - Send message (displayed as top message)
+  - Copy message
+  - Erase small portion of black area on the right side (displayed as bottom message)
+  
+  Notable observations:
+  - The message content has a 1 pixel border (padding/margin) on all sides
+    (except the bottom and corners) that can not be filled in. The bottom
+    border is correctly displayed for received messages, but the edit field has
+    an additional row of pixels that directly touch the message border on the
+    bottom.
+  - When any message is cloned, additional pixels that were masked on the top
+    screen become visible again in the edit field. This includes the bottom row
+    of pixels, as well as the two rows of pixels shown in the single line
+    message picture.
+
+### Message content
+
+![](../assets/pictochat-msg-pattern.png)
+![](../assets/ws-msg-pattern.png)
+
+- All messages with interesting content have NIFI header type 1 (CMD).
+- PictoChat messages appear to be sent over frames of length 0xf6 (246)
+  regardless of actual message size.
+- All frames appear to be sent exactly 5 times. 'New' frames have a value of
+  0xe004 at offset 0x0026, while resends have a value of 0xf000 instead.
+- There are a lot of messages with length 0xaa (170), these appear to include a
+  random 32-bit value at offset 0x0046.
+- The message content (suspected bitmap-like format) appears to be sent
+  unencrypted (patterns of 0x0 and 0x1 nibbles clearly visible in hexdump).
+
+## Unsure/notes
+
+- Is the endianness of the DS properly emulated?
+- Is the NIFI magic value also present in physical frames or is this something
+  MelonDS did?
+- The DS implemented WEP(?) encryption for connecting to home network
+  routers/APs, but is this encryption also used when the WiFi module is used in
+  local multiplayer mode? Does this even matter inside the emulator?
+