Documentation: Add PC Engines apu1

Describe how to run coreboot on the PC Engines apu1 mainboard.

Change-Id: If79693e893c4afe52bf1c9aa8017ac6f650a96e4
Signed-off-by: Piotr Kleinschmidt <piotr.kleinschmidt@3mdeb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32907
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

Documentation/mainboard/index.md

@@ -90,6 +90,10 @@ The boards in this section are not real mainboards, but emulators.
 
 - [RK9 Flash Header](roda/rk9/flash_header.md)
 
+## PC Engines
+
+- [APU1](pcengines/apu1.md)
+
 ## SiFive
 
 - [SiFive HiFive Unleashed](sifive/hifive-unleashed.md)

Documentation/mainboard/pcengines/apu1.md

@@ -0,0 +1,97 @@
+# PC Engines APU1
+
+This page describes how to run coreboot on PC Engines APU1 platform.
+
+## Technology
+
+```eval_rst
++------------+--------------------------------------------------------+
+| CPU        | AMD G series T40E APU                                  |
++------------+--------------------------------------------------------+
+| CPU core   | 1 GHz dual core (Bobcat core) with 64 bit support      |
+|            | 32K data + 32K instruction + 512KB L2 cache per core   |
++------------+--------------------------------------------------------+
+| DRAM       | 2 or 4 GB DDR3-1066 DRAM                               |
++------------+--------------------------------------------------------+
+| Boot       | From SD card, USB, mSATA, SATA                         |
++------------+--------------------------------------------------------+
+| Power      | 6 to 12W of 12V power                                  |
++------------+--------------------------------------------------------+
+| Firmware   | coreboot with support for iPXE and USB boot            |
++------------+--------------------------------------------------------+
+```
+
+## Flashing coreboot
+
+```eval_rst
++---------------------+--------------------------+
+| Type                | Value                    |
++=====================+==========================+
+| Socketed flash      | no                       |
++---------------------+--------------------------+
+| Model               | MX25L1606E               |
++---------------------+--------------------------+
+| Size                | 2 MiB                    |
++---------------------+--------------------------+
+| Package             | SOP-8                    |
++---------------------+--------------------------+
+| Write protection    | jumper on WP# pin        |
++---------------------+--------------------------+
+| Dual BIOS feature   | no                       |
++---------------------+--------------------------+
+| Internal flashing   | yes                      |
++---------------------+--------------------------+
+```
+
+### Internal programming
+
+The SPI flash can be accessed using [flashrom]. It is important to execute
+command with a `-c <chipname>` argument:
+
+    flashrom -p internal -c "MX25L1606E" -w coreboot.rom
+
+### External programming
+
+**IMPORTANT**: When programming SPI flash, first you need to enter apu1 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 pin layout
+included. Notice, that signatures at the schematic can be ambiguous:
+- J12 SPIDI = U35 SO = MISO
+- J12 SPIDO = U35 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
+provide communication with SPI devices. Example command to program SPI flash
+with OrangePi using linux_spi:
+
+    flashrom -w coreboot.rom -p linux_spi:dev=/dev/spidev1.0,spispeed=16000 -c
+    "MX25L1606E"
+
+
+**apu1 platform with marked in SPI header and SPI flash chip**
+
+![][apu1c1_flash]
+
+**SPI header pin layout**
+
+![][spi_header]
+
+
+### Schematics
+
+PC Engines APU platform schematics are available for free on PC Engines official
+site. Depending on the configuration:
+[apu1c](https://www.pcengines.ch/schema/apu1c.pdf) and
+[apu1d](https://www.pcengines.ch/schema/apu1d.pdf).
+
+
+[apu1c1_flash]: apu1c1.jpg
+[spi_header]: apu1_spi.jpg
+[flashrom]: https://flashrom.org/Flashrom