diff options
Diffstat (limited to 'share')
| -rw-r--r-- | share/man/man4/uart.4 | 53 |
1 files changed, 47 insertions, 6 deletions
diff --git a/share/man/man4/uart.4 b/share/man/man4/uart.4 index d520409..c0f49a1 100644 --- a/share/man/man4/uart.4 +++ b/share/man/man4/uart.4 @@ -25,7 +25,7 @@ .\" .\" $FreeBSD$ .\" -.Dd August 10, 2015 +.Dd December 9, 2015 .Dt UART 4 .Os .Sh NAME @@ -160,7 +160,9 @@ The API, accessed via is available on the tty device. To use the PPS capture feature with .Xr ntpd 8 , -symlink the tty device to +symlink the tty callout device +.Va /dev/cuau? +to .Va /dev/pps0. .Pp The @@ -175,15 +177,54 @@ it can be set in .Xr loader.conf 5 or .Xr sysctl.conf 5 . +.Pp The following capture modes are available: .Bl -tag -compact -offset "mmmm" -width "mmmm" -.It 0 +.It 0x00 Capture disabled. -.It 1 +.It 0x01 Capture pulses on the CTS line. -.It 2 -Capture pulses on the DCD line (default). +.It 0x02 +Capture pulses on the DCD line. +.El +.Pp +The following values may be ORed with the capture mode to configure +capture processing options: +.Bl -tag -compact -offset "mmmm" -width "mmmm" +.It 0x10 +Invert the pulse (RS-232 logic low = ASSERT, high = CLEAR). +.It 0x20 +Attempt to capture narrow pulses. .El +.Pp +Add the narrow pulse option when the incoming PPS pulse width is small +enough to prevent reliable capture in normal mode. +In narrow mode the driver uses the hardware's ability to latch a line +state change; not all hardware has this capability. +The hardware latch provides a reliable indication that a pulse occurred, +but prevents distinguishing between the CLEAR and ASSERT edges of the pulse. +For each detected pulse, the driver synthesizes both an ASSERT and a CLEAR +event, using the same timestamp for each. +To prevent spurious events when the hardware is intermittently able to +see both edges of a pulse, the driver will not generate a new pair of +events within a half second of the prior pair. +Both normal and narrow pulse modes work with +.Xr ntpd 8 . +.Pp +Add the invert option when the connection to the uart device uses TTL +level signals, or when the PPS source emits inverted pulses. +RFC 2783 defines an ASSERT event as a higher-voltage line level, and a CLEAR +event as a lower-voltage line level, in the context of the RS-232 protocol. +The modem control signals on a TTL-level connection are typically +inverted from the RS-232 levels. +For example, carrier presence is indicated by a high signal on an RS-232 +DCD line, and by a low signal on a TTL DCD line. +This is due to the use of inverting line driver buffers to convert between +TTL and RS-232 line levels in most hardware designs. +Generally speaking, a connection to a DB-9 style connector is an RS-232 +level signal at up to 12 volts. +A connection to header pins or an edge-connector on an embedded board +is typically a TTL signal at 3.3 or 5 volts. .Sh FILES .Bl -tag -width ".Pa /dev/ttyu?.init" -compact .It Pa /dev/ttyu? |
