Tock OT Notes 4/23/2020

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

Updates

• Silvestrs: Starting to use OT DIFs with Tock. UART worked well. Had to add to build.rs for linking.
• Also working on conditional compilation. So far cargo cfgs seems like the best approach.

Tock 1.5

• Brad: Release testing is in progress.
• Alistair: I've been testing apps, most don't work on OT.
  • Some inlcude ARM assembly.
  • Many libtock-c apps crash.
  • Some multiple apps do work.
• Long strings seem to be a problem (see issue). Something with hardware configuration and reboot.
• PMP doesn't need power of 2 rounding since using ToR.
• Garret: So far only limited PMP support in OT.
• Brad: We can mark OT support as preliminary.
• Alistair: Should we test HiFive1?
• Brad: I will.

Use Partial Crates

• Silvestrs: can rust compile only certain files from a crate? Such that we can substitute one peripheral for another?
• Garret: I'm not sure. You likely can use a cfg in mod.rs to control what is included in the compilation.
• Silvestrs: Also, how does the lowrisc/ibex crate split work?
• Alistair: Implementations of peripherals can be shared among multiple cores (ibex being one example).
• Brad: Modeled after SiFive structure.
• Alistair: Some things may be in the wrong directory currently, which could lead to confusion.

HMAC

• Alistair: Not many changes.
• Phil: Variable key lengths would have to be an async operation.
• Jon: FIFO full not FIFO empty.
• Alistair: Does that work?
• Jon: Changed, I haven't tested.

Testing

• Garret: Talked to Vadim. Questions about host testing. What is the hook point for code to interface with hardware abstractions? They are using dev_mem_read() and dev_mem_write() as a hook for testing.
• Alistair: Can QEMU be used?
• Garret: Not all peripherals are in QEMU. This is also heavy weight and difficult to keep in sync with changing hardware until tape-out.
• Higher level would apply more broadly, QEMU after tape-out maybe.
• Alistair: Well if you are already writing models.
• Garret: I still think it would be lower impact.