ECE 441 · Week 8
Modern Computer: Secure Infrastructure
From the public reset description, say what the first stage can check at reset and what it cannot.
Week 8 of 10 · Solitude
ECE 441 · Week 8 · In class
From the public reset description, say what the first stage can check at reset and what it cannot.
- Use the public description and the week-4 boot.
- A check that needs DRAM stays on the cannot side.
- Do not name a register the public description does not name.
ECE 441 · Week 8 · In class
The homework pair is one check a first stage can do with no DRAM, and one it cannot.
- The check with no DRAM is the first stage's own console line, the line only that build prints.
- The check it cannot do yet is a kernel image resident in DRAM.
- Copy that pair.
ECE 441 · Week 8 · Lecture
The machine at reset
- At reset the chip runs its boot ROM: fixed code from the factory, not rebuildable.
- The boot ROM finds the first stage on boot media and loads it into on-chip SRAM.
- DRAM is not usable yet: it has to be initialised and trained by software first.
- So the first stage starts with a small SRAM, the ROM's work, and whatever pins and clocks are up.
ECE 441 · Week 8 · Lecture
Reading the public reset description
- Note what it says the ROM does, in order: which media, in which order, how much it loads.
- Note what it says is set up when the first stage starts, and what is left to software.
- Where it says nothing, write "not stated". Do not fill in from another chip.
- Do not name a register the description does not name.
ECE 441 · Week 8 · Lecture
Sorting a check: can or cannot
| A check that needs | Side |
|---|---|
| Only SRAM, the ROM's work, and the console | Can, at reset |
| More data than SRAM holds | Cannot, yet |
| DRAM in any form | Cannot, yet |
| A driver the first stage does not have | Cannot, yet |
"Yet" matters: a later stage, with DRAM up, can do what the first stage cannot.
ECE 441 · Week 8 · Lecture
Evidence from the week-4 boot
- Your week-4 capture is time-stamped from power-on; it shows the order the stages ran in.
- Lines before DRAM is up come from code running in SRAM.
- Every "can" in the note points at something the board shows, in the capture.
ECE 441 · Week 8 · Lab
Lab
- From the public reset description and the week-4 boot, write what the first stage can check on this board and what it cannot.
- Second pass: mark one check that needs DRAM, and keep it on the "cannot" side.
- Assemble the lab hand-in: A one-page note of what the first stage can check at reset on this board, and what it cannot.
ECE 441 · Week 8 · Lab
Hand in
A one-page note of what the first stage can check at reset on this board, and what it cannot.
ECE 441 · Week 8 · Homework
Homework
- Write one check the lecture says a first stage can do with no DRAM, and one it cannot.
ECE 441 · Week 8 · Homework
Turn in
Those two checks.
ECE 441 · Week 8 · Read
Read
On the lab site: Module 12, A whole system, does not grade this reset note. This week is past Module 12.
ECE 441 · Week 8 · Next
Week 9
One device-tree or driver change, in the form an upstream project would read: a commit message, a diff, and a test log.