ECE 320 · Week 3
Modern Computer: Embedded Systems
No Monday lecture.
Week 3 of 10 · Das Frite
ECE 320 · Week 3 · In class
No Monday lecture.
- One lecture hour remains: how to mark a stage line that is already in the week-1 log.
- The boot-source names are the labels on the switch.
ECE 320 · Week 3 · In class
Copy the source names on the switch before you flip it, and copy the week-1 log line you will watch.
- That copy is the homework.
- In the lab, flip the switch, record the order the sources are tried, and boot the TA's first-stage image over USB from the bench PC.
- Do not rebuild it.
- Flip the switch back on the second pass.
ECE 320 · Week 3 · Lecture
The BootROM looks for the next stage
- The BootROM is code in the SoC that nobody can change. Its one job is to find and load the next stage.
- It tries boot sources in a fixed order and loads from the first one that holds a valid image.
- A boot switch or strap pins, read at reset, change which sources are tried and in what order.
- If nothing valid is found, many SoCs wait for an image over USB from a host PC.
ECE 320 · Week 3 · Lecture
Marking a line that is already in your log
- The BootROM prints little, and often before anything else: short codes or a few terse lines.
- Find the first line of your week-1 capture and ask which stage could have printed it.
- Find where the SRAM stage's own output begins; the lines before it belong to the BootROM.
- Mark on a copy of the log; keep the original untouched.
ECE 320 · Week 3 · Lecture
Recording a boot-source order
| Do | Why |
|---|---|
| Copy the switch labels before the flip | you need the names, not the positions |
| Capture from power-on, every time | the BootROM speaks only at the start |
| Change one thing per boot | so each log shows one cause |
| Flip back and boot once more | proves the board returned to normal |
ECE 320 · Week 3 · Lab
Lab
- No Monday lecture. Mark the BootROM lines on the week-1 log.
- Flip the boot switch, power on, and record the order the boot sources are tried. Boot the TA's first-stage image over USB from the bench PC and mark the lines that image prints. Do not rebuild it. Second pass: flip the switch back, boot once more, and keep that order in your notes.
ECE 320 · Week 3 · Lab
Lab (continued)
- Assemble the lab hand-in: The boot-source order observed after flipping the boot switch, with the BootROM lines and the TA first-stage lines marked on the log.
ECE 320 · Week 3 · Lab
Hand in
The boot-source order observed after flipping the boot switch, with the BootROM lines and the TA first-stage lines marked on the log.
ECE 320 · Week 3 · Homework
Homework
- From your week-1 boot log and the labels printed on the boot switch, copy the source names on the switch before you flip it.
ECE 320 · Week 3 · Homework
Turn in
The switch labels copied before the flip, and the week-1 log line you will watch.
ECE 320 · Week 3 · Read
Read
On the lab site: Module 3, The boot ROM, and Module 4, Loading the bootloader into SRAM. This week grades the observed order and the marked lines.
ECE 320 · Week 3 · Next
Week 4
A load address, and why the kernel and the device tree do not share one.