SYNOPSIS

jack.clock [options]

OPTIONS

-c

Set the drift correction interval in periods (default=64).

-p

Set the port number (default=57130).

DESCRIPTION

jack.clock publishes the transport state of the local JACK server as OSC packets over a UDP connection. jack.clock allows any OSC enabled application to act as a JACK transport client, receiving sample accurate pulse stream timing data, and monitoring and initiating transport state change.

Clients request to receive timing and change notification packets by sending a "request notification" packet, /jck_rn, to the jack.clock server. This packet has the form

/jck_rn category

where category is a bit mask that indicates what categories of notification packets are requested. The bit locations are:

#define	REQUEST_JCK_TK	0x00000001
#define	REQUEST_JCK_PL	0x00000002
#define	REQUEST_JCK_DC	0x00000004
#define	REQUEST_JCK_MC	0x00000008
#define	REQUEST_JCK_TC	0x00000010
#define	REQUEST_JCK_RC	0x00000020
#define	REQUEST_JCK_FC	0x00000040
#define	REQUEST_JCK_ALL	0xFFFFFFFF

Clients request notification messages to be sent to an address that is not that of the packet that requests the notification by sending a "request notification at" packet, /jck_ra. This packet has the form

/jck_ra category port-number host-name

where category is as for /jck_rn and where port-number and host-name give the address that notification should be sent to.

Once a client is registered subsequent /jck_rn and /jck_ra messages edit the category value for that client. To delete the client from the register send a request with a category value of negative one.

After requesting notification the client will receive all relevant timing packets sent by the server. All jack.clock timing packets are sent at the start of a JACK period as OSC message and have the same shape:

tag ntp utc frm arg...

where tag is the command name, and ntp, utc and frm are time stamps that indicate the same time point, the start of the JACK period when the packet was sent. ntp is an unsigned 64bit integer NTP value. utc is a double precision real valued representation of the UTC time. frm is a signed 64bit integer frame counter the absolute value of which is not defined but which increments synchronously with the ntp and utc time stamps. arg... is the set of tag specific arguments.

The timing packets sent by jack.clock are:

/jck_pl ntp utc frm p-ntp p-utc p-frm pulse

Pulse Location. This packet indicates that the nearest frame to the integer pulse pulse occurs at the time given by the time stamps p-ntp, p-utc and p-frm. The pulse number is one based. This packet is sent at the start of the JACK period in which the integer pulse will occur. This packet is not sent if the transport is stopped. This packet is sent before the /jck_tk packet for the same period.

/jck_tk ntp utc frm frame pulse

Period Tick. This packet is sent once per JACK period. The integer value frame is the transport location in frames, the double precision real value pulse is the transport location in pulses. The pulse value is read from an accumulator and is approximate only, the accumulator is corrected at each integer pulse location.

/jck_dc ntp utc frm ntp-dif utc-dif

Drift Correction. This packet is sent whenever the clock drift correction is run. The frequency of this is set by the -t option to the jack.clock server. The integer value ntp-dif is the NTP form of the corrected drift value and utc-dif the UTC form. Since JACK is a sample clock there is no frame drift value.

/jck_rc ntp utc frm state

Roll-state Change. This packet is sent whenever the JACK transport rolling state changes. The integer value state is zero if the transport has stopped and one if it has started.

/jck_tc ntp utc frm ppm

Tempo Change. This packet is sent whenever the JACK transport tempo changes. The double precision real value ppm is the new tempo in pulses per minute.

/jck_mc ntp utc frm ppc pt

Measure Change. This packet is sent whenever the JACK transport measure length or pulse type changes. The double precision real value ppc is the new measure length in pulses per cycle, the double precision real value pt is the pulse type.

/jck_fc ntp utc frm fps

Frame-rate Change. This packet is sent whenever the JACK sample rate changes. The double precision real value fps is the new sample rate in frames per second.

Clients can request a /jck_tk packet by sending a "request update" packet, /jck_ru, which requires no argument. The tick packet is sent only to the client that requested it, and is sent without consulting any category flag for that client. The precise interpretation of tick packets acquired in this manner is problematic.

Clients request a status packet by sending a "request status" packet, /jck_rs, which requires no argument. The server replies immediately with a status packet, /jck_st. The status packet is an OSC message and is not timestamped. It has the shape:

/jck_st fps ppm ppc pt status

where fps is the sample rate in frames per second, ppm is the tempo in pulses per minute, ppc is the measure length in pulses per cycle, pt is the pulse type, and status is the transport status. It is intended that a client will request a single status packet before requesting notification for all subsequent state changes.

Clients initiate a change in transport roll state by sending a "request transport operation" packet, /jck_rt, to the jack.clock server. It has the shape:

/jck_rt status

where status is the requested transport roll status and has the same meaning described earlier.

Clients initiate a change in transport location by sending a "request locate operation" packet, /jck_rl, to the jack.clock server. It has the shape:

/jck_rl location

where the single precision real value location is the requested transport location in seconds.

jack.clock implements only a subset of the OSC protocol. In particular it does not implement the patten matching rules and does not implement a scheduler for incoming messages.

jack.clock drops all unrecognized incoming packets.

AUTHORS

Rohan Drape.