DSi Atheros Wi-Fi support

[asiekierka]

This is the other of the two tough omissions from the DSi support of BlocksDS left.

Documentation

• GBAtek has most of what you need.
• The melonDS emulator has very limited emulation of the Wi-Fi chip's SDIO interface.

Prior art

• Atheros has developed an official non-upstreamed Linux driver ("ath6k"); however, some firmware operation details differ - as documented in GBAtek:
  • OpenMoko version (sw.18, GPLv2 only)
  • Newer version (3.0, MIT) released by Samsung. Note that files in other directories may be under other licensing terms, including proprietary ones - not all SoC vendors are known for paying attention to license headers.
  • Newer version (3.1_RC.514, MIT) released by Allwinner, among others. Disclaimer as above.
  • Newer versions (3.1_RC.563, 3.1_RC.667, 3.1_RC.734), as preserved by the LineageOS team.
  • ath6kl is a fork of the kernel driver only for the Linux kernel itself. This one is MIT-licensed.
  • In classic Nocash fashion, Nocash has transcribed the "dswifi" library to ASM, and patched it to provide DSi Wi-Fi support. Code available here, no clear licensing terms but they can probably be negotiated.
  • thomtl has experimented with deriving from this code with the C-based wifisdio proof of concept,
  • so has ahezard in no-dsi-wifi.

Challenges/Notes

• Should dswifi's sgIP still be maintained? It is rather janky, is not being updated to support new Internet standards, and nowadays one could use an existing library, such as:
  • lwIP (benefits heavily from good async threading - BlocksDS's current cothread scheduler is serviceable, but it may not be good enough; The One Everyone Uses),
  • smoltcp (very comfortable 0BSD license, but in Rust - which is not a problem for me; 3k+ stars on GitHub),
  • uIP6 (from Contiki-NG, may be difficult to extract; 1.1k+ stars on GitHub),
  • are there any others?
• If not, this would necessiate also rewriting/adapting the old NDS Wi-Fi communication code.

[AntonioND]

Regarding dswifi, I'm more than happy to add another WiFi library to the SDK and to leave dswifi as legacy.

[NightScript370]

I would also like to see built-in NiFi support. NesDS, GameYob & GBARunner2 all use their own implementation because upstream doesn't support it, but this would be a great chance to! It would actually benefit from here if we add the DSi WiFi chip support as well. For reference, Gericom hoped in 07/14/2020 that twl-WiFi would be 25x as fast as ntr-WiFi, which is critical when dealing with something as sensitive as timing.

[asiekierka]

I don't think 25x is achievable, given that even 3DS WiFi seems to only be 10-15x as fast, and that's on a good day.

NiFi/cross-console communication support should be a separate issue, as that has its own, separate prior art.

[asiekierka]

@NightScript370 I've opened an issue for general improvements to NTR-mode WiFi: https://github.com/blocksds/sdk/issues/64

[profi200]

It's not much but this might help too. It uses the TMIO driver from dsi_sdmmc. https://github.com/profi200/libn3ds/tree/master/source/arm11/drivers/wifi wifi.c is rather 3DS specific though.

[brais-sg]

Can this be used as a base for it? It appears to use lwIP too