[ntp:hackers] Serial port jitter

David L. Mills mills at udel.edu
Mon Jul 10 22:15:43 UTC 2006


Thanks for the info. The system in question is version 6.1, which puts 
the flags in /device.hints. However, the MUX happens to be a PCI card 
and the man sio for 6.1 says no flags are needed. I think I can figure 
engine runs; thanks for the ignition key.


Majdi S. Abbas wrote:

> On Thu, Jul 06, 2006 at 11:32:57PM +0000, David L. Mills wrote:
>> I searched the FreeBSD documentation looking for the little magic that
>> disables the FIFOs, but couldn't find it anywhere. Does someone here
>> know the magic potion?
> It appears to be in the man page for sio. You could
> place those device flags into the configuration for the kernel and
> rebuild for pre-5.x versions of FreeBSD.
> Here is an excerpt from the FreeBSD 4.10 GENERIC kernel config:
> -snip-
> # Serial (COM) ports
> device sio0 at isa? port IO_COM1 flags 0x10 irq 4
> device sio1 at isa? port IO_COM2 irq 3
> -snip-
> You can use the flags parameter to pass information to the driver:
> -snip-
> Meaning of flags:
> 0x00001 shared IRQs
> 0x00002 disable FIFO
> 0x00004 no AST/4 compatible IRQ control register
> 0x00008 recover sooner from lost output interrupts
> 0x00010 device is potential system console
> 0x00020 device is forced to become system console
> 0x00040 device is reserved for low-level IO (e. g. for remote
> kernel debugging)
> 0x00080 use this port for remote kernel debugging
> 0x0??00 minor number of master port
> 0x20000 device is assumed to use a 16650A-type (extended FIFO)
> chip
> -snip-
> If the host is FreeBSD 5.x or more recent, you can place these
> parameters in /etc/device.hints, which will override the default that
> enables the FIFO.
> PHK describes doing this in a post in the archives from October:
> http://support.ntp.org/pipermail/hackers/2005-October/001778.html
> In dmesg on startup these flags should be reflected:
> Jan 20 11:13:00 phantom /kernel: sio0 at port 0x3f8-0x3ff irq 4 flags 
> 0x10 on isa0
> Jan 20 11:13:00 phantom /kernel: sio0: type 16550A
> Jan 20 11:13:00 phantom /kernel: sio1 at port 0x2f8-0x2ff irq 3 on isa0
> Jan 20 11:13:00 phantom /kernel: sio1: type 16550A
> Hope this helps.
> I will look into tossing this into the wiki.
> --msa

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