[time-nuts] GPS message jitter (was GPS for Nixie Clock)

John Ackermann N8UR jra at febo.com
Tue Jul 19 07:48:44 EDT 2016

Long ago I measured the impact of the linux low_latency flag on a 16550 UART.  I don't know where that data is sitting now, but I remember that it made a significant difference.

> On Jul 18, 2016, at 9:59 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> jimlux at earthlink.net said:
>> except that virtually every UART in use today has some sort of buffering
>> (whether a FIFO or double buffering) between the CPU interface and the  bits
>> on the wire, which completely desynchronizes the bits on the wire  from the
>> CPU interface.
> The idea was to reduce the CPU load processing interrupts by batching things 
> up.
> Some of those chips generate an interrupt when the see a return or line-feed 
> character.
> Most of them have an option to disable that batching.  On Linux the setserial 
> command has a low_latency option.  I haven't measured the difference.  It 
> would be a fun experiment.
> -- 
> These are my opinions.  I hate spam.
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