Module 1 · Lab 2
What a board is
A board is a handful of large parts and many small ones. You learn what each large part does, find it on your own board and in its layout, and say what would go wrong at boot without it.
What a Das Frite is made of
| Part | What it is | Its role at boot |
|---|---|---|
| System-on-chip (Amlogic S805X) | Four Arm Cortex-A53 cores, a Mali-450 GPU, a video engine, a memory controller, on-chip SRAM, a boot ROM, one-time-programmable fuses, and controllers for USB, Ethernet, eMMC, SPI, I2C, UART, PWM and GPIO | Everything runs here; the boot ROM inside it is the first code to run |
| DRAM (512 MB DDR4, one chip on a 16-bit bus) | A separate memory chip beside the system-on-chip; volatile, lost at power-off | Unusable until software brings it up (module 5) |
| Storage: 16 MB SPI NOR flash, eMMC module socket, USB | Non-volatile places for the boot firmware and the OS. There is no microSD slot: the firmware lives in the SPI flash and the OS on a USB drive or an eMMC module | Where the boot ROM looks for the first stage (module 3) |
| Regulators | Four buck converters and a few linear regulators that turn the 5 V input into the rails | Must come up, in order, before anything runs (module 2) |
| Crystal (24 MHz) and reset supervisor | The reference clock that on-chip PLLs multiply, and the chip that holds reset until the supply is good | No clock and no reset release, no first instruction |
| I/O ports | USB Type-C (power and USB device mode), one USB 2.0 Type-A, Fast Ethernet with the PHY inside the system-on-chip, HDMI, composite video, an IR receiver, the 40-pin header | Mostly idle until the OS's drivers start them (modules 8–10) |
What a Solitude is made of
| Part | What it is | Its role at boot |
|---|---|---|
| System-on-chip (Amlogic S905D3) | Four Arm Cortex-A55 cores, a Mali-G31 GPU, a 1.2 TOPS AI accelerator, a video engine, a memory controller, on-chip SRAM, a boot ROM, one-time-programmable fuses, and controllers for USB, Ethernet, SD and eMMC, SPI, I2C, UART, PWM and GPIO | Everything runs here; the boot ROM inside it is the first code to run |
| DRAM (2 GB or 4 GB LPDDR4, 32-bit bus) | Separate memory chips beside the system-on-chip; volatile, lost at power-off | Unusable until software brings it up (module 5) |
| Storage: microSD slot, eMMC module socket, 16 MB SPI NOR flash | Non-volatile places for the boot firmware and the OS | Where the boot ROM looks for the first stage (module 3) |
| Regulators | Parts that turn the 5 V input into the lower voltages each part needs | Must come up, in order, before anything runs (module 2) |
| Crystal | A quartz reference clock; on-chip PLLs multiply it to the CPU and bus clocks | No clock, no first instruction |
| I/O ports and the chips behind them | A USB 3.0 hub with four ports, Gigabit Ethernet and its PHY, HDMI, camera and display connectors, the 40-pin header, the 3-pin UART header | Mostly idle until the OS's drivers start them (modules 8–10) |
Key ideas
- A system-on-chip puts what a PC spreads over a motherboard into one package. That is why so much of the board is the system-on-chip's supporting cast: memory, storage, power and connectors.
- The schematic and the layout are two views of the same board: the schematic says what connects to what; the layout says where each part sits and where each trace runs.
- Every connector on the edge of the board has a controller inside the system-on-chip, and often a second chip on the board (a PHY or a hub) between them.
- The two course boards make the trade-offs visible: Das Frite has one memory chip on a narrow bus and no card slot to keep it small and cheap; Solitude spends board area on wider memory, a USB 3.0 hub and camera and display connectors.
On the bench
In short, what you do in lab 2, where the steps are given in full:
- Find the system-on-chip, the DRAM, the SPI NOR flash, the regulators, the crystal and the connectors on the board in front of you.
- Find the same parts in the board layout viewer, and follow one trace from the system-on-chip to a connector.
- Open the schematic and fill in a table: part, function, and what the board would do at power-on without it.
Resources
| Resource | Use in this module |
|---|---|
| Das Frite board layout | Every part and trace, read from the board's own CAD data; select a part to see its footprint and pins |
| Board hardware schematics links | The schematic for every board |
| Das Frite product page | The board's page on libre.computer |
Resources
| Resource | Use in this module |
|---|---|
| Solitude board layout | Every part and trace, read from the board's own CAD data; select a part to see its footprint and pins |
| Board hardware schematics links | The schematic for every board |
| Solitude product page | Specifications |