idle kernel does not run at boot

jbqubit commented 9 months ago

One-Line Summary

The idle kernel does not run automatically after booting after startup kernel has exited.

Issue Details

Steps to Reproduce

Both idle kernel and startup kernel are on flash.
Reboot.

$ artiq_coremgmt log
[     0.000067s]  INFO(runtime): NAR3/Zynq7000 starting...
[     0.005240s]  INFO(runtime): gateware ident: brittonlab-kaslisoc-fun
[     0.016762s]  INFO(libboard_zynq::i2c): PCA9548 detected
[     0.176426s]  INFO(runtime::rtio_clocking): using 100MHz reference to make 125MHz RTIO clock with PLL
[     0.549549s]  INFO(libboard_artiq::si5324): waiting for Si5324 lock...
[     2.930830s]  INFO(libboard_artiq::si5324):   ...locked
[     2.939995s]  INFO(runtime::rtio_clocking): RTIO PLL locked
[     2.950751s]  INFO(libboard_zynq::i2c): PCA9548 detected
[     2.987599s]  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
[     3.005658s]  INFO(libboard_artiq::drtio_routing): could not read routing table from configuration, using default
[     3.015832s]  INFO(libboard_artiq::drtio_routing): routing table: RoutingTable { 0: 0; 1: 1 0; 2: 2 0; 3: 3 0; 4: 4 0; }
[     3.032774s]  INFO(runtime::comms): Loading startup kernel...
[     3.038523s]  INFO(runtime::rtio_mgt::drtio): [DEST#0] destination is up
[     3.045228s]  INFO(runtime::comms): Starting startup kernel...
[     3.051049s]  INFO(runtime::kernel::core1): kernel starting
[     6.926713s]  INFO(runtime::kernel::core1): kernel finished
[     6.932277s]  INFO(runtime::comms): Startup kernel finished!
[     7.437087s]  INFO(libboard_zynq::eth): eth: got Link { speed: S1000, duplex: Full }
[    91.935033s]  INFO(runtime::mgmt): received connection

Observe (above) that the idle kernel did not run after the startup kernel finished.
Run some other kernel that ends quickly.

[   181.878810s]  INFO(runtime::kernel::core1): kernel starting
[   185.011007s]  INFO(runtime::mgmt): received connection
[   185.754475s]  INFO(runtime::kernel::core1): kernel finished
[   185.760036s]  INFO(runtime::comms): peer closed connection
[   185.765510s]  INFO(runtime::comms): Loading idle kernel
[   185.770751s]  INFO(runtime::comms): Running idle kernel
[   185.775961s]  INFO(runtime::kernel::core1): kernel starting
[   188.540284s]  INFO(runtime::mgmt): received connection