TashTalk USB

Since its now available, the Phase 2 Addendum is a good document to review: https://bitsavers.org/pdf/apple/com...se_2_Protocol_Specification_Addendum_1989.pdf

Inside AppleTalk covers this, but not all together in one place.

@iigs123, does the ImageWriter appear to other Localtalk clients when the iPrint is turned off? LocalTalk has no concept of networks over the line and devices like the ImageWriter generally use non-extended DDP packets if no router is present. If I recall, one of the NBP related bugs involved the card not filling out the extended DDP header response correctly, although this shouldn't be a problem on a non-routed network.

The other bug is that it basically puts trash data in the DDP checksum field, so if TailTalk is verifying DDP checksums, it could be dropping the packets. Note that by default, Apple's network stacks on Macs do not verify DDP checksums.

I dont believe we care at all about DDP checksums - I found most devices seem to just set it to zero so I've never bothered to check them. Wouldn't I need to use NBP broadcast requests though for it to work for LocalTalk to EtherTalk? TailTalk only does NBP Lookups today as it doesn't know anything about routers so I guess the iPrint wont forward it on if I understood your previous post correctly.

Thanks so much for the addendum too, will enjoy reading through that tonight.

On a single network (no router), the client should broadcast a NBPLookup packet to the network. On networks with a router, the client sends a NBPBroadcastRequest packet directly to the router, which will in turn broadcast the NBPLookup to all its ports or forward it to other routers.