Tock OT Notes 5/07/2020

Present:

• Brad Campbell (Chair), University of Virginia
• Jon Flatley, Google
• Silvestrs Timofejevs, lowRISC
• Johnathan Van Why, Google
• Garret Kelly, Google
• Alistair Francis, Western Digital
• Phil Levis, Stanford
• Alphan Ulusoy, Google

Updates

• Silvestrs: Downstream Tock updates

  • https://github.com/lowRISC/opentitan/issues/2139

• Alphan: Working on OT syscall latency. 3 PRs to Tock.

• Brad: Do you have some sense of the improvement?

• Alphan: 8-9x improvement. about 5000 down to 400 cycles

• Don't set MPU if already configured. Use mapcell for stored state. Don't collect debug info.

• Brad: Some work on HiFive1b. Various updates needed in Tock to convert the rev a board to the rev b.

Chrome OS Roadmap

• Garret: Two chips, one that isn't OpenTitan, but an OT as well.
• Vadim can present.
• TODO: Garret will invite Vadim to present.

QEMU Testing

• Alistair: Moving to rexpect (expect in Rust) for QEMU testing. PR open.
• Brad: What tests do you see adding? Kernel and userspace?
• Alistair: rexpect is very flexible. Should be able to support any tests.
• Brad: What about user interactive tests?
• Alistair: rexpect will be able to nicely handle that as well.

PRs

• Phil: Re: one byte reads in OT UART, subtlety there not well documented.
• Brad: Right, callbacks only from interrupt handlers not clear.
• Brad: We did have a thought about using capabilities passed in from the interrupt handler.
• Johnathan: This has also appeared in libtock-rs.