external clock stopping not reported by core devices

[jbqubit]

Bug Report

One-Line Summary

Unexpected behavior for clock configuration.

Issue Details

Steps to Reproduce

• First confirm that some clock options do work.
• $ artiq_coremgmt config write -s rtio_clock ext0_bypass
• Reboot kasli.
• Observe that RTIO output ceases if the clock SMA is disconnected. Good.
• $ artiq_coremgmt config write -s rtio_clock ext0_synth0_100to125
• Reboot kasli.
• RTIO output continues if the clock SMA is disconnected. Incorrect.
• There are no errors in the log.

$ artiq_coremgmt log
[     0.000067s]  INFO(runtime): NAR3/Zynq7000 starting...
[     0.005240s]  INFO(runtime): gateware ident: brittonlab-kaslisoc-fun
[     0.016769s]  INFO(libboard_zynq::i2c): PCA9548 detected
[     0.176654s]  INFO(runtime::rtio_clocking): using 100MHz reference to make 125MHz RTIO clock with PLL
[     0.549799s]  INFO(libboard_artiq::si5324): waiting for Si5324 lock...
[     2.931105s]  INFO(libboard_artiq::si5324):   ...locked
[     2.940995s]  INFO(runtime::rtio_clocking): RTIO PLL locked
[     2.951745s]  INFO(libboard_zynq::i2c): PCA9548 detected
[     2.988547s]  INFO(runtime::comms): network addresses: MAC=fc-0f-e7-07-7b-df IPv4=192.168.1.45 IPv6-LL=fe80::fe0f:e7ff:fe07:7bdf IPv6: no configured address
[     3.006591s]  INFO(libboard_artiq::drtio_routing): could not read routing table from configuration, using default
[     3.016840s]  INFO(libboard_artiq::drtio_routing): routing table: RoutingTable { 0: 0; 1: 1 0; 2: 2 0; 3: 3 0; 4: 4 0; }
[     3.031914s]  INFO(runtime::rtio_mgt::drtio): [DEST#0] destination is up
[     6.744917s]  INFO(runtime::mgmt): received connection
[     7.031090s]  INFO(libboard_zynq::eth): eth: got Link { speed: S1000, duplex: Full }
[    14.470506s]  INFO(runtime::kernel::core1): kernel starting
[    18.346171s]  INFO(runtime::kernel::core1): kernel finished
[    18.352536s]  INFO(runtime::comms): peer closed connection
[    25.457981s]  INFO(runtime::kernel::core1): kernel starting
[    29.333642s]  INFO(runtime::kernel::core1): kernel finished
[    29.339847s]  INFO(runtime::comms): peer closed connection
[    30.875135s]  INFO(runtime::mgmt): received connection

Your System (omit irrelevant parts)

• ARTIQ version: v7.8180.21c6f57
• Hardware is Kasli-SOC v1.1.1.
• Running in nix development environment for kasli-soc release-7.
• Boot is via run_local.sh