- v0.5 – Wireless GBA netplay: trade and battle in Pokémon FireRed/LeafGreen

New: GBA wireless games

• GBA_netplay.rbf: the MiSTer GBA core with an emulated GBA Wireless
  Adapter on the link port. Games that use Nintendo's adapter play over the
  internet: Apotris, Pokémon FireRed, LeafGreen and Emerald (the Union Room:
  battles and trades), and homebrew built on gba-link-connection.
• This is not lockstep: each MiSTer runs its own game, and the two adapters
  talk to each other over the network. The players may run different games
  that talk to each other (FireRed and LeafGreen).
• In the OSD: Hardware → Link Port → Wireless Adapter, then Netplay →
  Host on one MiSTer and Join on the other, and load the game. Then use
  the game's own wireless menu, as on real GBAs.
• The core handles the adapter's handshake and words; the Main binary answers
  each command (ported from gpSP's adapter emulation, GPL-2.0-or-later) and
  carries the adapter's packets over a reliable, ordered link between the two
  MiSTers, directly or through the lobby server.
• Loading the game again keeps the room: the other player's MiSTer follows
  without loading its own game again.
• A lost packet is sent again after about 1.5 round trips, so the game's data
  is held up for tens of milliseconds, not 100.
• netplay.log shows the link's round trip, resends, and how fast the
  adapter's commands are answered, every 10 seconds.
• To try it: Apotris, a free game by akouzoukos with 2-player battles over
  the adapter, from https://akouzoukos.com/apotris/downloads (put
  Apotris.gba in games/GBA).

Tested on hardware: two MiSTers over the internet through the lobby server on a
Raspberry Pi: Pokémon FireRed/LeafGreen battles and a trade in the Union Room, and
gba-link-connection's LinkUniversal_stress ROM (packet loss and packet sync,
65,534 packets each without a loss; ping 26 to 47 ms with a 20 ms network round
trip). In simulation: the core's serial port and adapter against Pokémon's own
wireless library, with the Main binary's answers late and out of order.

Scripts

• netplay_on no longer saves an older netplay binary as MiSTer_offline
  when you update: your normal binary stays there. netplay_off says so when
  MiSTer_offline is a netplay binary (from an older netplay_on); then
  update_all or downloader brings the normal binary back.

Server

• GBA rooms accept any GBA game, so FireRed and LeafGreen find each other.
  Update the server too.

Known limits

• Two players (the adapter allows five). No wireless multiboot (one cartridge
  for both). Savestates and rewind are off while the adapter is on.
• Each command the game sends to the adapter is answered by the Main binary,
  usually in 0.2 to 0.5 ms; about 1 in 100 takes 1 to 3 ms. The games tested
  handle this. Moving the answers for the data commands into the core is
  planned.
• When the host loads the core again (not just the game), the other player
  loads their game again too.
• Through a server on the same network as one of the players, the link goes
  through the server; the extra step is about a millisecond.

Download: mister-netplay-v0.5.zip below has everything (SD card files, server, quick start). Check it with md5sums.txt.