ECE 320 · Week 2
Modern Computer: Embedded Systems
Rail order on a supplied trace, and which regulator feeds the SoC.
Week 2 of 10 · Das Frite
ECE 320 · Week 2 · In class
Rail order on a supplied trace, and which regulator feeds the SoC.
- The trace is the one the section supplies.
- Mark the order the rails rise, and mark when reset releases.
- One regulator on that trace feeds the SoC.
- Name it from the labels on the trace.
ECE 320 · Week 2 · In class
The homework names two rails that must already be up before the SoC regulator can start, and why that order matters.
- Take the names from the lecture trace.
- These notes do not print a second rail list.
ECE 320 · Week 2 · Lecture
Two rails reach the header
- 5 V
- 3.3 V
- Ground
Other pins are dimmed. Colours as on the Das Frite pinout, where each pin's name is. The square pad is pin 1.
ECE 320 · Week 2 · Lecture
From one input to many rails
- The board takes one input voltage; the SoC, DRAM and I/O each need their own lower voltages.
- Each of those supplies is a rail, made by a regulator from the input or from another rail.
- The schematic and the trace both use the rail's net name; that name is what you write down.
| Regulator | How it works |
|---|---|
| Buck (switching) | switches and filters; efficient at high current |
| LDO (linear) | drops the excess as heat; quiet, simple |
ECE 320 · Week 2 · Lecture
How a sequence is built
- A regulator starts when its enable (EN) input goes high.
- Many regulators drive a power-good (PG) output once their rail is in range.
- Wire one rail's power-good to the next regulator's enable and the order is set in hardware.
- A dedicated sequencer or a power-management IC can do the same with timed steps.
ECE 320 · Week 2 · Lecture
Reading a power-up trace
| On the trace | Means |
|---|---|
| A rail leaves 0 V and ramps | its regulator was enabled |
| The rail settles at its value | it is up; mark this time |
| Reset goes inactive | the SoC may start running |
Order the rails by the time each settles, using one threshold for all of them. Reset release comes last.
ECE 320 · Week 2 · Lab
Lab
- On the supplied power-up trace, mark the order the rails rise and when reset releases.
- Name the regulator that feeds the SoC. Second pass: mark the same trace in a second color and keep the first marking.
- Assemble the lab hand-in: The supplied power-up trace with the rail order marked, and the name of the regulator that feeds the SoC.
ECE 320 · Week 2 · Lab
Hand in
The supplied power-up trace with the rail order marked, and the name of the regulator that feeds the SoC.
ECE 320 · Week 2 · Homework
Homework
- From the lecture, name two rails that must already be up before the SoC regulator can start.
ECE 320 · Week 2 · Homework
Turn in
Those two rail names and why the order matters.
ECE 320 · Week 2 · Read
Read
On the lab site: Module 2, First power-on and voltage rails, explains sequencing. This week hands in the marked trace and the SoC regulator.
ECE 320 · Week 2 · Next
Week 3
No Monday lecture.