Re: DECstation 5000/200 timekeeping

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> Umm, the 5000/200 is R3000-based and has no high-precision timer
>> hardware of any kind available.  [...]
> Mouse - what timecounter info is printing during boot?

I think I said that in another message (sent after yours, I think),
but, to put it here in proper response order:

DECstation 5000/200 (3MAX)
total memory = 32768 KB
avail memory = 28272 KB
timecounter: Timecounters tick every 3.906 msec
mainbus0 (root)
cpu0 at mainbus0: MIPS R3000 CPU (0x220) Rev. 2.0 with MIPS R3010 FPC Rev. 2.0
cpu0: 64KB/4B direct-mapped Instruction cache, 64 TLB entries
cpu0: 64KB/4B direct-mapped write-through Data cache
tc0 at mainbus0: 25 MHz clock
ibus0 at tc0 slot 7 offset 0x0
mcclock0 at ibus0 addr 0x1fe80000: mc146818 or compatible
dz0 at ibus0 addr 0x1fe00000: DC-7085, 4 lines
lkkbd0 at dz0 line 0
wskbd0 at lkkbd0 mux 1
vsms0 at dz0 line 1
wsmouse0 at vsms0 mux 0
le0 at tc0 slot 6 offset 0x0: address 08:00:2b:1b:b7:5f
le0: 32 receive buffers, 8 transmit buffers
asc0 at tc0 slot 5 offset 0x0: NCR53C94, 25MHz, SCSI ID 7
scsibus0 at asc0: 8 targets, 8 luns per target
timecounter: Timecounter "clockinterrupt" frequency 256 Hz quality 0
scsibus0: waiting 2 seconds for devices to settle...
sd0 at scsibus0 target 1 lun 0: <SEAGATE, ST373307LC, 0003> disk fixed
sd0: 69809 MB, 49855 cyl, 4 head, 716 sec, 512 bytes/sect x 142969680 sectors
sd0: sync (200.00ns offset 15), 8-bit (5.000MB/s) transfers, tagged queueing

> This should give some details on that the kernel is using for a clock
> source.

Besides the above, sysctl says

kern.clockrate: tick = 3906, tickadj = 15, hz = 256, profhz = 256, stathz = 256

kern.timecounter.choice = clockinterrupt(q=0, f=256 Hz) dummy(q=-1000000, f=1000000 Hz)
kern.timecounter.hardware = clockinterrupt

> Also, does "vmstat -i" show anything about missed clock interrupts?

No:

[Pmax] 22> vmstat -i
interrupt                                     total     rate
pmax serial0                                   1226        0
pmax ether                                  1034850       18
pmax scsi                                   1335845       24
clock intr                                 14203678      256
Total                                      16575599      298

[Pmax] 23> 

> Both of my 5000/200's fail to power up :(

:-( indeed.

Until I determined that the cable I had was bad, I suspected mine might
have broken Ethernet.  I'm glad that was not the case; I did set it up
with SLIP on ttyD2, but the 5000/200 has dz serial ports, which can't
do faster than 19200, so it was s-l-o-w.  If I couldn't've done
anything better, I might have done SLIP over both ttyD2 and ttyD3, with
some jiggery-pokery to handle console output...or perhaps done away
with lkkbd0 and vsms0 and used those as serial ports too, if the
hardware turns out to be capable of that (presumably I'd need level
shifters, but that's totally doable).  Striping across three or four
ports doesn't make up for a factor of 500+ slowdown (that's the
approximate slowdown of 19200 SLIP as compared to 10Mb Ethernet), but
every little bit helps when dealing with networking that slow.

Fortunately, my machine's Ethernet _isn't_ broken - I just need to find
one of my pieces of thinnet co-ax. :-)

How complicated is turbochannel from a hardware designer's perspective?
Or is that not publicly known?  I'm wondering if it'd be practical to
build a TC board providing proper clock capabilities.  Even if just a
sampleable free-running counter, once calibrated that could substitute
for the cycle counter the r3k apparently lacks.

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