croll@miracl.dec.com (07/30/86)
This posting is in response to a previous posting that was in response to a posting I didn't see. The posting was about VAX 8200/8300 console lines and contained a lot of misinformation. This is intended to correct this information. (The original posting also asked some questions about the DMB32 and the DECserver-200, which I'm not qualified to answer.) This is about 120 lines long. The original comments are denoted by >> and were from ARPA%"W._Michael_Terenyi%QZCOM.MAILNET@MIT-MULTICS.ARPA" and the reply, denoted by >, was from ritcv!awp8101 (Andrew Potter). >>There are 4 serial lines on the processor, one for the console and >>three spares. I was told to stay away from them, because using one >>of this serial lines will cost 10% of the CPU power due to a bug in >>microcode. Is this really true? If yes, is there a date for a new >>microcode version? There is no microcode bug. There are two attributes of the serial lines on the processor, which affect performance. The first attribute of these lines is that they are unbuffered: there is no DMA and no SILO, either. They work fine for low speed devices, or for reasonably high-speed devices that are used for output and infrequently. If you use them for input, you run the risk of losing characters, and the risk increases as baud rate increases. Each line has a maximum speed of 19.2 Kbaud, but at that speed, the lines will be unusable because you'll lose so many characters. The second attribute is that the lines are serviced by the CPU microcode. For each serial line, there are four CPU Internal Processor Registers (receive CSR, receive data buffer, transmit CSR, transmit data buffer). Obviously, when the microcode is off servicing the serial lines, it isn't doing useful work executing instructions. When the lines are running at high speeds, you wind up doing nothing buy servicing serial line interrupts. Because of these attributes of the serial lines, VMS recommends that you not use these lines at speeds higher than 1200 baud. > ... but I think the build in ports are >for the console ports for the 2 processors. Since VMS cannot see the console >ports on the processor that running as slave, the most you will see is >is two ports OPA0: and OPA1. No, this is not correct. In an 8300 system, EACH processor has 4 serial lines. The lines on the attached (or slave) processor are not connected to anything. The lines on the primary processor are attached to the four ports on the back of the cabinet. The first line (the top one, or line 0) is the primary processor's console. The other three are available for anything you want. The slave's serial lines are not available, for two reasons: they're not wired to anything you can hook a terminal to, and VMS won't support them. By default, you will only see the console line when VMS comes up. This is called OPA0:. If you want to see the other lines, you have to use SYSGEN and explicitly connect them, in a way that's similar to connecting the console floppy: $ RUN SYS$SYSTEM:SYSGEN CONNECT SLU=1 CONNECT SLU=2 CONNECT SLU=3 EXIT $ These lines will then appear as devices TCA1, TCA2, TCA3. Again, in an 8300 system, only the primary processor's console lines can be connected in this way. >>What are this serial lines intended for? Are there special limits >>for speed? Do they have modem signals? Can they be used for an >>asynchronous DECnet link? >I dont know for sure, but if tradition holds then one will have >modem control for Remote diagnosis and the other wont. In any case >you wont have access to those control signals via "SET TERM", probably >the only way is via the console program, The >>> prompt. These lines can be used for anything you like. The VMS terminal driver supports them just like it supports DMB32 or DZ11 terminal lines. There are no modem signals. The speed is limited, nominally to 1200 baud, but with the caveats I mentioned above. I believe that you can use them for an async DECnet link, although I've never tried it. SET TERMINAL works, too. There is much more detailed information about these serial lines in the KA820 Processor Technical Manual (EK-KA820-TM-001). You can order this through your local sales office, or you can call either (617) 351-4323 or (603) 884-9129 for information, or you can write to Digital Equipment Corporation Publishing and Circulation Services NR3 10 Forbes Road Northboro, MA 01532 >>Why is the VAX8300 sold with 12 MB of memory only, despite the possible >>maximum of 14 MB? I was told not to buy 2 MB extra memory. >The 8200/8300 has a fixed number of BI slots. Since the 8300 has >an extra processor card, something had to go. That something is >most likely a memory board. (you could toss your DMB-32 board). The VAX 8200 has a maximum memory of 14 MB; the VAX 8300 has a maximum memory of 12 MB because one memory board is removed to make room for the extra processor. There are only 12 slots in the VAXBI backplane shipped with the 8200/8300 package, and you use 6 of them for 12 MB of memory (2 MB/board). The other six are used for DWBUA (BI-Unibus adapter), DMB32, KDB50 (2 slots), and the CPU. This leaves one extra slot, and you can either put more memory in it (VAX 8200) or another CPU (VAX 8300). John Croll VAX 8200/8300 Engineering Digital Equipment Corporation LTN1-1/F15 P.O. Box 1123 Littleton, MA 01460 ...decvax!decwrl!dec-rhea!dec-oblio!croll