# Simple Network Time Protocol Client

There is are four SNTP (Simple Network Time Protocol) clients implemented using zeptoIP, for each combination of RP2040 and RP2350 and of IPv4 and IPv6. As an SNTP clients they use only one NTP server, as opposed to NTP clients which use multiple SNTP servers. They are not automatically included with the code loaded with `extra/rp_common/pico_w_net_ipv4_all.fs` or `extra/rp_common/pico_w_net_ipv6_all.fs` and it is up to the user whether to compile them to flash or to RAM.

Note that they give the time as a 32.32 unsigned fixed-point number of seconds from 1 Jan 1900 00:00:00 GMT. Consequently, if one tries to treat this number as a conventional S31.32 signed fixed-point number, it will (i.e. as of writing) to be treated as negative until the current NTP era ends.

Kiss-of-death (including reduce-rate) packets are supported. Also, the address resolved with DNS is regularly re-resolved so as to properly use DNS server pools where multiple DNS server as behind a single DNS name.

### `ntp-ipv4` and `ntp-ipv6`

The `ntp-ipv4` and `ntp-ipv6` modules contain the following word:

##### `ntp-port`
( -- port )

This returns the default NTP port, i.e 123.

The `ntp` module contains the following class:

#### `<ntp-ipv4>` and `<ntp-ipv6>`

The `<ntp-ipv4>` and `<ntp-ipv6>` classes inherit from the `<endpoint-handler>` class defined in the `endpoint-process` module. They have the following constructor:

##### `new`
( ip-interface sntp-client -- )

This constructor takes an instance of `<ipv4-interface>`, for `<ntp-ipv4>`, or `<ipv6-interface>`, for `<ntp-ipv6>`, *ip-interface* and the `<ntp>` instance being constructed. *ip-interface* will be used by the NTP client for looking up the NTP server via DNS and communicating with it.

The `<ntp-ipv4>` and `<ntp-ipv6>` classes have the following methods:

##### `init-ntp`
( dns-name dns-name-len port sntp-client -- )

This method starts the SNTP client with *dns-name* and *dns-name-len* being the hostname used to lookup the NTP server (note that using NTP servers by fixed IPv4 addresses is _not_ supported) using the port *port* (typically `ntp-port`, i.e. 123).

##### `current-time@`
( sntp-client -- D: time )

Get the current time as a 32.32 unsigned fixed-point number of seconds from 1 Jan 1900 00:00:00 GMT. Note that if `time-set?` does not return `true` this value will be invalid (and will be fixed to `0.`).

##### `time-set?`
( sntp-client -- time-set? )

Get whether a time has been established for the SNTP client. This will initially return `false` and will only return `true` after a (relatively short) delay provided the NTP server can be looked up and responds to SNTP requests.