# PC Engines APU2

This page describes how to run coreboot on PC Engines APU2 platform.

## Technology

```{eval-rst}
+------------+---------------------------------------------------------------+
| CPU        | AMD G series GX-412TC                                         |
+------------+---------------------------------------------------------------+
| CPU core   | 1 GHz quad Puma core with 64 bit support                      |
|            | 32K data + 32K instruction cache per core, shared 2MB L2 cache|
+------------+---------------------------------------------------------------+
| DRAM       | 2 or 4 GB DDR3-1333 DRAM                                      |
+------------+---------------------------------------------------------------+
| Boot       | From SD card, USB, mSATA SSD, SATA                            |
+------------+---------------------------------------------------------------+
| Power      | 6 to 12W of 12V power                                         |
+------------+---------------------------------------------------------------+
| Firmware   | coreboot with support for iPXE and USB boot                   |
+------------+---------------------------------------------------------------+
```

## Required proprietary blobs

To build working coreboot image some blobs are needed.

```{eval-rst}
+-----------------+---------------------------------+---------------------+
| Binary file     | Apply                           | Required / Optional |
+=================+=================================+=====================+
| amdfw.rom*      | AMD Platform Security Processor | Required            |
+-----------------+---------------------------------+---------------------+
| AGESA.bin       | AGESA Platform Initialization   | Required            |
+-----------------+---------------------------------+---------------------+
| xhci.bin        | AMD XHCI controller             | Optional            |
+-----------------+---------------------------------+---------------------+
```
(\*) - package containing all required blobs for PSP. Directory, in which all
blobs are listed and available is: *3rdparty/southbridge/amd/avalon/PSP*

## Flashing coreboot

```{eval-rst}
+---------------------+--------------------------+
| Type                | Value                    |
+=====================+==========================+
| Socketed flash      | no                       |
+---------------------+--------------------------+
| Model               | W25Q64                   |
+---------------------+--------------------------+
| Size                | 8 MiB                    |
+---------------------+--------------------------+
| Package             | SOIC-8                   |
+---------------------+--------------------------+
| Write protection    | jumper on WP# pin*       |
+---------------------+--------------------------+
| Dual BIOS feature   | no                       |
+---------------------+--------------------------+
| Internal flashing   | yes                      |
+---------------------+--------------------------+
```
(\*) - It is used in normal SPI mode, but can be dangerous when using Quad SPI
Flash. Then, pull-down resistors should be considered rather than jumper.

### Internal programming

The SPI flash can be accessed using [flashrom].

    flashrom -p internal -w coreboot.rom

### External programming

**IMPORTANT**: When programming SPI flash, first you need to enter apu2 in S5
(Soft-off) power state. S5 state can be forced by shorting power button pin on
J2 header.

The external access to flash chip is available through standard SOP-8 clip or
SOP-8 header next to the flash chip on the board. Notice that not all boards
have a header soldered down originally. Hence, there could be an empty slot with
8 eyelets, so you can solder down a header on your own. The SPI flash chip and
SPI header are marked in the picture below. Also there is SPI header and SPI
flash pin layout included. Depend on using header or clip there are important
rules:
- using header J6 - don't connect 1,7,8 pins
- using clip U23 - don't connect 3,7,8 pins

Also signatures at the schematic can be ambiguous:
- J6 SPIDI = U23 SO = MISO
- J6 SPIDO = U23 SI = MOSI

There is no restrictions as to the programmer device. It is only recommended to
flash firmware without supplying power. External programming can be performed,
for example using OrangePi and Armbian. You can exploit linux_spi driver which
provides communication with SPI devices. Example command to program SPI flash
with OrangePi using linux_spi:

    flashrom -f -w coreboot.rom -p linux_spi:dev=/dev/spidev1.0,spispeed=16000

**apu2 platform with marked in SPI header and SPI flash chip**

![][apu2_flash]

**SPI header pin layout**

![][spi_header]

## Schematics

PC Engines APU2 [platform schematics](https://pcengines.ch/schema/apu2d.pdf)
are available for free on PC Engines official site. Both configurations
(2GB/4GB) have the same PCB and schematic.

[apu2_flash]: apu2.jpg
[spi_header]: apu2_spi.jpg
[flashrom]: https://flashrom.org/Flashrom