woslyng@arc.CDN (Fred Woslyng) (11/21/87)
Is is possible to connect an Atari 520 or 1040ST running a Macintosh emulator (such as Magic Sac) to a TOPS network? Macs are connected to the TOPS network through the serial port. One problem is Macs have a special chip to drive the serial port at 230K baud. Also, the custom chip may be doing more than just driving the port at high speed. If you have tried an Atari ST on TOPS or have an opinion to express, please reply to either info-atari16 or directly to me. Thanks. Fred Woslyng ARPA: woslyng%arc.cdn%ubc.csnet@relay.cs.net Computing Department BITNET: woslyng@arc.cdn Alberta Research Council CDNnet: woslyng@arc.cdn Edmonton, Alberta CSNET: woslyng%arc.cdn@ubc.csnet Canada UUCP: ...alberta!arc.cdn!woslyng
cute@sphinx.UUCP (11/21/87)
In article <441*woslyng@arc.cdn> woslyng@arc.CDN (Fred Woslyng) writes: >Is is possible to connect an Atari 520 or 1040ST running a Macintosh >emulator (such as Magic Sac) to a TOPS network? > >Macs are connected to the TOPS network through the serial port. One problem >is Macs have a special chip to drive the serial port at 230K baud. Also, the >custom chip may be doing more than just driving the port at high speed. If ^^^^^^^^^^^ The Macintosh serial ports are driven by a standard Zilog 8530 SCC on the motherboard. It was chosen probably because it has such high-speed capabilities. The fact that the AppleTalk device drivers (TOPS runs on AppleTalk) and hardware absolutely require this chip makes it unlikely you'll be able to do what you want without extra hardware. Unless of course Atari ALSO uses said chip for THEIR serial ports. Anyone know? l i n e s -- ...ihnp4!gargoyle!sphinx!cute (insert pithy quote here)
rwa@auvax.UUCP (Ross Alexander) (11/22/87)
In article <2698@sphinx.uchicago.edu>, cute@sphinx.uchicago.edu (John Cavallino) writes: > In article <441*woslyng@arc.cdn> woslyng@arc.CDN (Fred Woslyng) writes: > >Is is possible to connect an Atari 520 or 1040ST running a Macintosh > >emulator (such as Magic Sac) to a TOPS network? > The Macintosh serial ports are driven by a standard Zilog 8530 SCC on the > motherboard. [...] Unless of course Atari ALSO uses said chip for > THEIR serial ports. Anyone know? Atari uses two different chips for serial i/o. The modem port is driven by a Motorola MC68901 "Multi-Function Peripheral" (MFP) chip, while the midi port gets its bits from a Motorola MC6850 "Asynchronous Communications Interface Adaptor" (ACIA). We can essentailly forget about the midi port in this discussion because 1) it's clocked at a fixed rate and thus we can't tweak the baud to match Appletalk & 2) it's an asynchronous-only part (ACIA, right ;-). OK, now the MFP is a little more flexible than the ACIA. We can get it to run async up to 62.5 Kbps, and synchronously up to 1Mbps [an aside: my source for _all_ this stuff is the Mostek MK68901 write-up that came with my (otherwise almost *totaly* useless) Developer's Kit. Sure hope it's better than some of the other info; flame, flame!!]. However, there's a rub (and I don't have my Zilog books handy, but I'm pretty sure about this), and that's that the Z8350 is a fairly clever little fellah and knows about things like HDLC bit stuffing and framing, and how to generate/check CRC's on the fly, and station address recognition, and a lot of other stuff which is good to be handled by the serial chip rather than the CPU, especially in a machine as lethargic as a Mac (well, a Mac's lethargic compared to a Sun 3, and that's what I'm used to...) when you're in a network environment and there's a lot of traffic on the backbone which isn't addressed to you in particular, but you have to watch it all anyway because some might be for you eventually. Good grief, what a horrible sentence! But I think that's the case. Whereas the 68901 can sync up to the input datastream and receive/xmit but it has no idea of bit stuffing or CRC's or any of that good stuff. Which means somebody else (and it's not going to be the power supply, foax) is going to have to supply the smarts. Now assuming Appletalk is built on top of all the nice HDLC stuff that the Z8350 manages so nicely (seems like a safe bet to me; I would have done it that way myself, and Apple never puts hardware in their machines that they don't use to the max), the MFP is at a bit of a disadvantage. The CPU is going to have to do all the clever stuff; and I would expect the overhead to be pretty painful. Especially all the bit stuffing; lots of shifting and masking and partial-word assembly. CRC's, on the other hand, are easy enough. Still, the overhead gets you down, especially if there are other stations out there on the net - the 68000 is standing there taking interrupts off the 68901, checking the station address, finds the packet's not for him, great - we can throw it away, but in the meantime the user (that's US foax) is standin there waiting for a compile to get done or whatever and its not going along very fast :-(. Any Appletalk gurus out there? I'm just looking at datasheets and thinking about implementations and bottlenecks. But it's for sure the 68901 is not a very clever synchronous part at all, at all. Ross Alexander, Athabasca University alberta!auvax!rwa
egisin@orchid.waterloo.edu (Eric Gisin) (11/23/87)
In the reference article, Ross Alexander writes about appletalk and the ST's 68901. I don't think it would be feasible. Appletalk has a bit rate of 230K, or about 80K characters per second. The Mac's serial controller is interrupt driven, but has a 3 byte silo. The 68901 has a single byte buffer, and would have process interrupts in 12 useconds, or do polled IO. It would also have to do bit stuffing on the fly to find flag sequences. The 68000 is not quite fast enough for all that.
dsmall@well.UUCP (David Small) (11/26/87)
In the referenced article, the question is asked: Can the ST under the Magic Sac run TOPS local area network. We have TOPS here in house, and it isn't compatible with the Magic Sac. As many here on the net already surmised, TOPS talks directly with the SCC in the Mac to achieve high speed. The Atari has no comparable hardware and thus can't be connected. This is also why we've never supported Appletalk on the Magic Sac. -- Thanks, Dave Dave Small / Engineer / Data Pacific (Magic Sac folks) (and complete Net novice, but I'm trying..)