Clean up (or if antipodic: down) some of the msgbuf stuff.
Use an inline function rather than a macro for timecounter delta.
Maintain process "on-cpu" time as 64 bits of microseconds to avoid
needless second rollover overhead.
Avoid calling microuptime the second time in mi_switch() if we do
not pass through _idle in cpu_switch()
This should reduce our context-switch overhead a bit, in particular
on pre-P5 and SMP systems.
WARNING: Programs which muck about with struct proc in userland
will have to be fixed.
Reviewed, but found imperfect by: bde
"time" wasn't a atomic variable, so splfoo() protection were needed
around any access to it, unless you just wanted the seconds part.
Most uses of time.tv_sec now uses the new variable time_second instead.
gettime() changed to getmicrotime(0.
Remove a couple of unneeded splfoo() protections, the new getmicrotime()
is atomic, (until Bruce sets a breakpoint in it).
A couple of places needed random data, so use read_random() instead
of mucking about with time which isn't random.
Add a new nfs_curusec() function.
Mark a couple of bogosities involving the now disappeard time variable.
Update ffs_update() to avoid the weird "== &time" checks, by fixing the
one remaining call that passwd &time as args.
Change profiling in ncr.c to use ticks instead of time. Resolution is
the same.
Add new function "tvtohz()" to avoid the bogus "splfoo(), add time, call
hzto() which subtracts time" sequences.
Reviewed by: bde
on the IOAPIC being connected to the 8254 timer interrupt.
Verify that timer interrupts are delivered. If they aren't, attempt
a fallback to mixed mode (i.e. routing the timer interrupt via the 8259 PIC).
interrupts are masked, and EOI is sent iff the corresponding ISR bit
is set in the local apic. If the CPU cannot obtain the interrupt
service lock (currently the global kernel lock) the interrupt is
forwarded to the CPU holding that lock.
Clock interrupts now have higher priority than other slow interrupts.
the signal handling latency for cpu-bound processes that performs very
few system calls.
The IPI for forcing an additional software trap is no longer dependent upon
BETTER_CLOCK being defined.
it runs at a constant frequency. This was less of an issue before,
because the TSC only interpolated in the HZ intervals, but now where
the timecounter is used all the way, this becomes much more visible.
Nit: Fix a printf which triggered the bde-filter.
Highlights:
* Simple model for underlying hardware.
* Hardware basis for timekeeping can be changed on the fly.
* Only one hardware clock responsible for TOD keeping.
* Provides a real nanotime() function.
* Time granularity: .232E-18 seconds.
* Frequency granularity: .238E-12 s/s
* Frequency adjustment is continuous in time.
* Less overhead for frequency adjustment.
* Improves xntpd performance.
Reviewed by: bde, bde, bde
is "acquired". This fixes a TSC biasing error of about 10 msec when
pcaudio is active.
Update `time' before calling hardclock() when timer0 is being released.
This is not known to be important.
Added some delays in writertc(). Efficiency is not critical here, unlike
in rtcin(), and we already use conservative delays there.
Don't touch the hardware when machdep.i8254_freq is being changed but
the maximum count wouldn't change. This fixes jitter of up to 10 msec
for most small adjustments to machdep.i8254_freq. When the maximum
count needs to change, the hardware should be adjusted more carefully.
actually faster (more than 20% faster for zeroing 1 MB at boot time).
This fixes pessimized copying and zeroing on K6's and perhaps on other
CPUs that are misclassified as i586's.
Wrappered and enabled by the define BETTER_CLOCK (on by default in smpyests.h)
apic_vector.s also contains a small change I (smp) made to eliminate
the double level INT problem. It seems stable, but I haven't the tools
in place to prove it fixes the problem.
Reviewed by: smp@csn.net
Submitted by: Tor Egge <Tor.Egge@idi.ntnu.no>
make isa_dmacascade, isa_dmastart, isa_dmadone, and find_isadev MUCH
easier to be found by starting them at the beginging of the line...
remove braces inside of ifdef RESOURCE_CHECK... found by % in vi...
there is a natural place to initialize `safepri' in a future commit.
Spinoffs:
- spl0() gets called in the unlikely event that isa is not configured.
- configure() has better control over enabling interrupts.
- it is now less unclear that interrupts aren't actually enabled early.
Rev.1.48 of autoconf.c seems to have done the opposite of what was
intended - moving the isa_configure() call delayed the spl0() side
effect.
Added some comments about the bogons. Removed the splhigh() call since
it is a no-op.
in <machine/cpu.h>. Moved the declarations to <machine/cputypes.h>.
Fixed style bugs in the moved code. Fixed everything that depended on
the nested include. Don't include <machine/cpu.h> (in the changed files)
unless something in it is used directly.
It seems I didn't count my 0's properly when adding the new masks into
icu_vector.s pushing SWI_AST_MASK off the end of the array and screwing
up the indexing for SWI_CLOCK_MASK.
Fix the bug icu_vector.s and also reformat the code in both icu_vector.s and
apic_vector.s so that it will be much harder to make the same mistake in
the future.
Submitted by: Bruce Evans <bde@zeta.org.au>
machine generates an NMI for each floating point error, just like an old XT.
Since it is ISA only, reading the EISA status port yields 0xff, which would
give a spurious EISA panic. The simplest thing to do is to ignore the 0xff.
these structs for conflics...
it still exist that two PnP cards can colide, but this is up to the user
to make sure it doesn't happen...
other modifications to pnp.c to format output properly, and hide more
output behind bootverbose flag...
fix some bugons in pnp.h that would of made it difficult for inclusion
in external programs (for import of pnpinfo)
mode, the slash is a comment leader, while under non-elf it is a divide
symbol (what a concept! :-). Theoretically, #APP/#NO_APP can change this
but that doesn't seem to mesh too well with macros and line continuation.
Add a simplelock to deal with disable_intr()/enable_intr() as used in UP kernel.
UP kernel expects that this is enough to guarantee exclusive access to
regions of code bracketed by these 2 functions.
Add a simplelock to bracket clock accesses in clock.c: clock_lock.
Help from: Bruce Evans <bde@zeta.org.au>
and the sound driver which uses auto dma.
The dma interface functionality remains however it now checks
to see if a dma is operating in auto dma mode and if so it bypasses
the busy flag check . I have modified the sound driver 3.5 to
adjust for this new behavior and tested it under FreeBSD 3.0 -current
This patch also includes the new function isa_dmastop.
Submitted by: Amancio Hasty <hasty@rah.star-gate.com>
irqs can't work (at best, the first one attached wins). It used to
be necessary to skip this check because of bogus irqs in the sound
drivers, but the sound drivers have been fixed, except possibly the
OSS ones.
region protected by the simplelock 'cpl_lock'.
Notes:
- this code is currently controlled on a section by section basis with
defines in machine/param.h. All sections are currently enabled.
- this code is not as clean as I would like, but that can wait till later.
- the "giant lock" still surrounds most instances of this "cpl region".
I still have to do the code that arbitrates setting cpl between the
top and bottom halves of the kernel.
- the possibility of deadlock exists, I am committing the code at this
point so as to exercise it and detect any such cases B4 the "giant lock"
is removed.
Made NEW_STRATEGY default.
Removed misc. old cruft.
Centralized simple locks into mp_machdep.c
Centralized simple lock macros into param.h
More cleanup in the direction of making splxx()/cpl MP-safe.
Work done by BSDI, Jonathan Lemon <jlemon@americantv.com>,
Mike Smith <msmith@gsoft.com.au>, Sean Eric Fagan <sef@kithrup.com>,
and probably alot of others.
Submitted by: Jnathan Lemon <jlemon@americantv.com>
Mask the read value from the count register in order to return zero correctly
after TC, as per intel datasheet : "If it is not autoinitialised, this
register will have a count of FFFFH after TC"
comments. Remove reduntant extra addition that was unncessary, and
unneeded mask (asuming inb works correctly).
Submitted by: Stephen McKay <syssgm@dtir.qld.gov.au>
handlers don't skew the results of isa_dmastatus. The function can be
safely called with interrupts disabled.
Submitted by: Stephen McKay <syssgm@dtir.qld.gov.au>
- removed TEST_ALTTIMER.
- removed APIC_PIN0_TIMER.
- removed TIMER_ALL.
apic_vector.s:
- new algorithm where a CPU uses try_mplock instead of get_mplock:
if successful continue as before.
if fail set ipending bit, mask INT (to avoid recursion), cleanup & iret.
This allows the CPU to return to successful work, while the ISR will be run
by the CPU holding the lock as part of the doreti dance.
- added Xcpustop IPI code to support stop_cpus()/restart_cpus().
it is off by default, enable via smptests.h:TEST_CPUSTOP
intr_machdep.h:
- moved +ICULEN to lower level.
- added entry for Xcpustop.
This eliminates a lot of #ifdef SMP type code. Things like _curproc reside
in a data page that is unique on each cpu, eliminating the expensive macros
like: #define curproc (SMPcurproc[cpunumber()])
There are some unresolved bootstrap and address space sharing issues at
present, but Steve is waiting on this for other work. There is still some
strictly temporary code present that isn't exactly pretty.
This is part of a larger change that has run into some bumps, this part is
standalone so it should be safe. The temporary code goes away when the
full idle cpu support is finished.
Reviewed by: fsmp, dyson
top of the hardware interrupt handlers. Apparently this is slightly
faster with the bit scanning instruction that looks these up - this set of
changes reverts the original change.
Reviewed by: bde
- vector.s <- stub called by i386/exception.s
- icu_vector.s <- UP
- apic_vector.s <- SMP
Split icu.s into UP and SMP specific files:
- ipl.s <- stub called by i386/exception.s (formerly icu.s)
- icu_ipl.s <- UP
- apic_ipl.s <- SMP
This was done in preparation for massive changes to the SMP INTerrupt
mechanisms. More fine tuning, such as merging ipl.s into exception.s,
may be appropriate.
be (eventually) architecture independent. It provides an emulation
of the ISA interrupt registration function register_intr(), but that
function does no longer manipulated the interrupt controller and
interrupt descriptor table, but calls the architecture dependent
function setup_icu() for that purpose.
After the ISA/EISA bus code has been modified to directly call the new
interrupt registartion functions (intr_create() and intr_connect()),
the emulation of register_intr() should be dropped.
The C level interrupt handler function should take a (void*) argument,
and the function pointer type (inthand2_t) should defined in some other
place than isa_device.h.
This commit is a pre-requisite for the removal of the PCI specific shared
interrupt code.
Reviewed by: dfr,bde
- doesn't break my system.
- NOT yet verified on the affected motherboard.
Stifle an annoying dma_start busy message for the sound cards.
Submitted by: "John S. Dyson" <toor@dyson.iquest.net>
simplifies some assumptions and stops some code compile problems.
This should fix the compile hiccup in PR#3491, but smp kernel profiling
isn't likely to be fixed by this.
Peter Wemm <peter@spinner.DIALix.COM>, Steve Passe <smp@csn.net>
removed all the IPI_INTS code.
made the XFAST_IPI32 code default, renaming Xfastipi32 to Xinvltlb.
cleanup of i386/isa/isa_device.h to eliminate SMP dependancies:
made the id_irq member of struct isa_device an u_int.
made the id_drq member of struct isa_device an int.
removed all other '#ifdefs' concerning SMP & APIC_IO.
removed SMP/APIC_IO dependancies from if_ze.c.
There are various options documented in i386/conf/LINT, there is more to
come over the next few days.
The kernel should run pretty much "as before" without the options to
activate SMP mode.
There are a handful of known "loose ends" that need to be fixed, but
have been put off since the SMP kernel is in a moderately good condition
at the moment.
This commit is the result of the tinkering and testing over the last 14
months by many people. A special thanks to Steve Passe for implementing
the APIC code!
have successfully built, booted, and run a number of different ELF
kernel configurations, including GENERIC. LINT also builds and
links cleanly, though I have not tried to boot it.
The impact on developers is virtually nil, except for two things.
All linker sets that might possibly be present in the kernel must be
listed in "sys/i386/i386/setdefs.h". And all C symbols that are
also referenced from assembly language code must be listed in
"sys/i386/include/asnames.h". It so happens that failure to do
these things will have no impact on the a.out kernel. But it will
break the build of the ELF kernel.
The ELF bootloader works, but it is not ready to commit quite yet.
print "at <not configured>" for iobase == -1 (autodetect not happens)
and not print anything for iobase == -2 (none)
Old code treat this two special config numbers as big port numbers.
I have code to calibrate the overhead fairly accurately, but there
is little point in using it since it is most accurate on machines
where an estimate of 0 works well. On slow machines, the accuracy
of DELAY() has a large variance since it is limited by the resolution
of getit() even if the initial delay is calibrated perfectly.
Use fixed point and long longs to speed up scaling in DELAY().
The old method slowed down a lot when the frequency became variable.
Assume the default frequency for short delays so that the fixed
point calculation can be exact.
Fast scaling is only important for small delays. Scaling is done
after looking at the counter and outside the loop, so it doesn't
decrease accuracy or resolution provided it completes before the
delay is up. The comment in the code is still confused about this.
called early for console i/o. The timer is usually in BIOS mode
if it isn't explicitly initialized. Then it counts twice as fast
and has a max count of 65535 instead of 11932. The larger count
tended to cause infinite loops for delays of > 20 us. Such delays
are rare. For syscons and kbdio, DELAY() is only called early
enough to matter for ddb input after booting with -d, and the delay
is too small to matter (and too small to be correct) except in the
PC98 case. For pcvt, DELAY() is not used for small delays (pcvt
uses its own broken routine instead of the standard broken one),
but some versions call DELAY() with a large arg when they unnecessarily
initialize the keyboard for doing console output. The problem is
more serious for pcvt because there is always some early console
output.
Guard against the i8254 timer being partially or incorrectly
initialized. This would have prevented the endless loop.
Should be in 2.2.
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
is still broken - it doesn't restore the floating point state.
2.2-BETA users should disable it using npx0 flags 0x04 the same as
2.2-ALPHA users should have.
user supplies a bad address, because they push a lot of stuff that the
fault handler doesn't know about onto the stack. This has been broken
for more than half a year despite being tested for almost half a year
in -current.
negative-logic flags (flags 0x01 and 0x02 for npx0, defaulting to unset = on).
This changes the default from off to on. The options have been in current
for several months with no problems reported.
Added a boot-time negative-logic flag for the old I5886_FAST_BCOPY option
which went away too soon (flag 0x04 for npx0, defaulting to unset = on).
Added a boot-time way to set the memory size (iosiz in config, iosize in
userconfig for npx0).
LINT:
Removed old options. Documented npx0's flags and iosiz.
options.i386:
Removed old options.
identcpu.c:
Don't set the function pointers here. Setting them has to be delayed
until after userconfig has had a chance to disable them and until after
a good npx0 has been detected.
machdep.c:
Use npx0's iosize instead of MAXMEM if it is nonzero.
support.s:
Added vectors and glue code for copyin() and copyout().
Fixed ifdefs for i586_bzero().
Added ifdefs for i586_bcopy().
npx.c:
Set the function pointers here.
Clear hw_float when an npx exists but is too broken to use.
Restored style from a year or three ago in npxattach().
handlers if interrupts are nested more than a few (3) deep. This
only reduces the maximum nesting level by 1 with the standard
drivers unless there is a related bug somewhere, but can't hurt
much (the worst case is returning to hoggish interrupt handler like
wdintr(), but such interrupt handlers hurt anyway).
Fixed a previously harmless race incrementing the interrupt nesting
level.
This should be in 2.1.6 and 2.2.
hardware interrupt counts add up to the total. Previously, software
interrupts generated by splz() were counted in the total. These
software interrupts seem to be very rare - there have apparently been
0 of them on freefall among the last 352448857 interrupts.
(1) deleted #if 0
pc98/pc98/mse.c
(2) hold per-unit I/O ports in ed_softc
pc98/pc98/if_ed.c
pc98/pc98/if_ed98.h
(3) merge more files by segregating changes into headers.
new file (moved from pc98/pc98):
i386/isa/aic_98.h
deleted:
well, it's already in the commit message so I won't repeat the
long list here ;)
Submitted by: The FreeBSD(98) Development Team
instead of 0 if there is no input.
syscons.c:
Added missing spl locking in sccncheckc(). Return the same value as
sccngetc() would. It is wrong for sccngetc() to return non-ASCII, but
stripping the non-ASCII bits doesn't help.
make it more intelligible, improve the partially bogus locking, and
allow for a ``quick re-acquiration'' from a pending release of timer 0
that happened ``recently'', so it was not processed yet by clkintr().
This latter modification now finally allows to play XBoing over
pcaudio without losing sounds or getting complaints. ;-) (XBoing
opens/writes/closes the sound device all over the day.)
Correct locking for sysbeep().
Extensively (:-) reviewed by: bde
Testing with the high frequency of 20000 Hz (to find problems) only found
the problem that this frequency is too high for slow i386's.
Disable interrupts while setting the timer frequency. This was unnecessary
before rev.1.57 and forgotten in rev.1.57. The critical (i8254) interrupts
are disabled in another way at boot time but not in the sysctl to change
the frequency.
enable flag instead of enable_intr() to restore it to its usual state.
getit() is only called from DELAY() so there is no point in optimising
its speed (this wasn't so clear when it was extern), and using
enable_intr() made it inconvenient to call DELAY() from probes that need
to run with interrupts disabled.
All new code is "#ifdef PC98"ed so this should make no difference to
PC/AT (and its clones) users.
Ok'd by: core
Submitted by: FreeBSD(98) development team
ansi and traditional cpp.
The nesting rules of macros are different, which required some changes.
Use __CONCAT(x,y) instead of /**/.
Redo some comments to use /* */ rather than "# comment" because the ansi
cpp cares about those, and also cares about quote matching.
time. The results are currently ignored unless certain temporary options
are used.
Added sysctls to support reading and writing the clock frequency variables
(not the frequencies themselves). Writing is supposed to atomically
adjust all related variables.
machdep.c:
Fixed spelling of a function name in a comment so that I can log this
message which should have been with the previous commit.
Initialize `cpu_class' earlier so that it can be used in startrtclock()
instead of in calibrate_cyclecounter() (which no longer exists).
Removed range checking of `cpu'. It is always initialized to CPU_XXX
so it is less likely to be out of bounds than most variables.
clock.h:
Removed I586_CYCLECTR(). Use rdtsc() instead.
clock.c:
TIMER_FREQ is now a variable timer_freq that defaults to the old value of
TIMER_FREQ. #define'ing TIMER_FREQ should still work and may be the best
way of setting the frequency.
Calibration involves counting cycles while watching the RTC for one second.
This gives values correct to within (a few ppm) + (the innaccuracy of the
RTC) on my systems.
regarding apm to LINT
- Disabled the statistics clock on machines which have an APM BIOS and
have the options "APM_BROKEN_STATCLOCK" enabled (which is default
in GENERIC now)
- move around some of the code in clock.c dealing with the rtc to make
it more obvios the effects of disabling the statistics clock
Reviewed by: bde
channel at the same time. The functions isa_dma_acquire() and
isa_dma_release() should be used in all ISA drivers which call isa_dmastart().
This can be used more generally to register the usage of DMA channels in
any driver, but it is required for drivers using isa_dmastart() and friends.
Clean up sanity checks, error messages, etc.
Remove isa_dmadone_nobounce(), it is no longer needed
Reviewed by: bde
Always delay using one inb(0x84) after each i/o in rtcin() - don't
do this conditional on the bogus option DUMMY_NOPS not being defined.
If you want an optionally slightly faster rtcin() again, then inline
it and use a better named option or sysctl variable. It only needs
to be fast in rtcintr().
clock interrupts.
Keep a 1-in-16 smoothed average of the length of each tick. If the
CPU speed is correctly diagnosed, this should give experienced users
enough information to figure out a more suitable value for `tick'.
fd and wt drivers need bounce buffers, so this normally saves 32K-1K
of kernel memory.
Keep track of which DMA channels are busy. isa_dmadone() must now be
called when DMA has finished or been aborted.
Panic for unallocated and too-small (required) bounce buffers.
fd.c:
There will be new warnings about isa_dmadone() not being called after
DMA has been aborted.
sound/dmabuf.c:
isa_dmadone() needs more parameters than are available, so temporarily
use a new interface isa_dmadone_nobounce() to avoid having to worry
about panics for fake parameters. Untested.
variants, idea taken from NetBSD clock.c.
At least year calculation was wrong, pointed by Bruce.
Use different strategy to store year for BIOS without RTC_CENTURY
was overlapping with another file, and making some undesirable behavior a
little worse - it's triggering a bug in config that appears to have been
there for some time (before the options files, anyway.)
feature of the ICU. auto-EOI on the slave is not safe, however, so it
remains an option. Killed religious FASTER_NOP when writing the ICU.
Reviewed by: bde
overflows.
It sure would be nice if there was an unmapped page between the PCB and
the stack (and that the size of the stack was configurable!). With the
way things are now, the PCB will get clobbered before the double fault
handler gets control, making somewhat of a mess of things. Despite this,
it is still fairly easy to poke around in the overflowed stack to figure
out the cause.
- Don't print out meaningless iCOMP numbers, those are for droids.
- Use a shorter wait to determine clock rate to avoid deficiencies
in DELAY().
- Use a fixed-point representation with 8 bits of fraction to store
the rate and rationalize the variable name. It would be
possible to use even more fraction if it turns out to be
worthwhile (I rather doubt it).
The question of source code arrangement remains unaddressed.
bit set. I broke stat_imask in Dec 1994 and update_intr_masks() has
copied the breakage to intr_mask[8] since Mar 1995. This can cause
the RTC to stop interrupting in rare cases (under loads heavy enough
for a new RTC interrupt to occur at a critical time just before Xintr8
finishes handling the previous one) and may have caused worse problems.
Convert the remaining sysctl stuff to the new way of doing things.
the devconf stuff is the reason for the large number of files.
Cleaned up some compiler warnings while I were there.
almost every time someone uses an address. This file is probably not
the right place to keep track of the unused addresses (or used
addresses :->).
Fixed comments on #endif's to match code.
Added defines for ASC and GSC sizes. This file is not the right place
to keep track of scanner addresses, but while there here and we
pretend to keep track of unused addresses, the sizes need to be here
too.
Sorted IO_*SIZE defines.
in here to do some conflict detection. The new code doesn't do conflict
detection yet, but it will be implemented in another way.
aic7770.c moved to i386/eisa
/dev/random is now a part of the kernel! you will need to make
the device in /dev: sh MAKEDEV random
and take a look at some test code in src/tools/test/random.
the kernel. ppp_tty.c goes to some lengths to minimise the inter-layer
calling (including a soft ISR). ppp_tty.c takes care of the soft masking
that was needed still.
(I've discovered that bugs in this area show up within an hour if the
masking was not correct.. :-} This combination has proven stable on
specialix serial ports, although there was some concern about the softtty
parts of sio/cy and netisr colliding - but Bruce has fixed that now)
This code will only be included in your kernel if you have
'options DEVRANDOM', but that will fall away in a couple of days.
Obtained from: Theodore Ts'o, Linux
free-run and doing a subtract in microtime() rather than resetting the
counter to zero at every clock tick. In combination with the changes to
kern_clock.c, this should eliminate all the immediately obvious sources
of systematic jitter in timekeeping on Pentium machines.
the first one in the config has priority. They can be switched using
userconfig().
i386/i386/conf.c:
Initialize the shared syscons/pcvt cdevsw entry to `nx'.
Add cdevsw registration functions.
Use devsw functions of the correct type if they exist.
i386/i386/cons.c:
Add renamed syscons entry points to constab.
i386/i386/cons.h:
Declare the renamed syscons entry points.
i386/i386/machdep.c:
Repeat console initialization after userconfig() in case the current
console has become wrong. This depends on cn functions not wiring down
anything important.
sys/conf.h:
Declare new functions.
i386/isa/isa.[ch]:
Add a function to decide which display driver has priority. Should be
done better.
i386/isa/syscons.c:
Rename pccn* -> sccn*.
Initialize CRTC start address in case the previous driver has moved it.
i386/isa/syscons.c, i386/isa/pcvt/*
Initialize the bogusly shared variable Crtat dynamically in case the
stored value was changed by the previous driver.
Initialize cdevsw table from a template.
Don't grab the console if another display driver has priority.
i386/isa/syscons.h, i386/isa/pcvt/pcvt_hdr.h:
Don't externally declare now-static cdevsw functions.
i386/isa/pcvt/pcvt_hdr.h:
Set the sensitive hardware flag so that pcvt doesn't always have lower
priority than syscons. This also fixes the "stupid" detection of the
display after filling the display with text.
i386/isa/pcvt/pcvt_out.c:
Don't be confused the off-screen cursor offset 0xffff set by syscons.
kern/subr_xxx.c:
Add enough nxio/nodev/null devsw functions of the correct type for syscons
and pcvt.
