mb/acer/g43t-am3: Add documentation

Signed-off-by: Michael Büchler <michael.buechler@posteo.net>
Change-Id: I0e296b3efbff0260f32badc699f1062f9885fa53
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56838
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

2 files changed, 181 insertions, 0 deletions

diff --git a/Documentation/mainboard/acer/g43t-am3.md b/Documentation/mainboard/acer/g43t-am3.md
new file mode 100644
index 000000000000..2e9b8d658c02
--- /dev/null
+++ b/Documentation/mainboard/acer/g43t-am3.md
@@ -0,0 +1,177 @@
+# Acer G43T-AM3
+
+The Acer G43T-AM3 is a microATX-sized desktop board. It was used for the
+Acer models Aspire M3800, Aspire M5800 and possibly more.
+
+## Technology
+
+```eval_rst
++------------------+--------------------------------------------------+
+| Northbridge      | Intel G43 (called x4x in coreboot code)          |
++------------------+--------------------------------------------------+
+| Southbridge      | Intel ICH10R (called i82801jx in coreboot code)  |
++------------------+--------------------------------------------------+
+| CPU socket       | LGA 775                                          |
++------------------+--------------------------------------------------+
+| RAM              | 4 x DDR3-1066                                    |
++------------------+--------------------------------------------------+
+| SuperIO          | ITE IT8720F                                      |
++------------------+--------------------------------------------------+
+| Audio            | Realtek ALC888S                                  |
++------------------+--------------------------------------------------+
+| Network          | Intel 82567V-2 Gigabit Ethernet                  |
++------------------+--------------------------------------------------+
+```
+
+There is no serial port. Serial console output is possible by soldering
+to a point at the corresponding Super I/O pin and patching the
+mainboard-specific code accordingly.
+
+## Status
+
+### Working
+
+Tests were done with SeaBIOS 1.14.0 and slackware64-live from 2019-07-12
+(linux-4.19.50).
+
++ Intel Core 2 processors at up to FSB 1333
++ All four DIMM slots at 1066 MHz (tested 2x2GB + 2x4GB)
++ Integrated graphics (libgfxinit)
++ HDMI and VGA ports
++ Both PCI slots
++ Both PCI-e slots
++ USB (8 internal, 4 external)
++ All six SATA ports
++ Onboard Ethernet
++ Onboard sound card with output on the rear stereo connector
++ PS/2 mouse and keyboard
+    + With SeaBIOS, use CONFIG_SEABIOS_PS2_TIMEOUT, tested: 500
+    + With FILO it works without further settings
++ Temperature readings from the Super I/O (including the CPU temperature
+  via PECI)
++ Super I/O EC automatic fan control
++ S3 suspend/resume
++ Poweroff
+
+### Not working
+
++ DDR3 memory with 512Mx8 chips (G43 limitation)
++ 4x4GB of DDR3 memory (works, but showed a single bit error within one
+  pass of Memtest86+ 5.01)
++ Super I/O voltage reading conversions
+
+### Untested
+
++ Other audio jacks or the front panel header
++ S/PDIF output
++ On-board Firewire
++ Wake-on-LAN
+
+## Flashing coreboot
+
+```eval_rst
++-------------------+---------------------+
+| Type              | Value               |
++===================+=====================+
+| Socketed flash    | No                  |
++-------------------+---------------------+
+| Model             | Macronix MX25L1605D |
++-------------------+---------------------+
+| Size              | 2 MiB               |
++-------------------+---------------------+
+| Package           | 8-Pin SOP           |
++-------------------+---------------------+
+| Write protection  | No                  |
++-------------------+---------------------+
+| Dual BIOS feature | No                  |
++-------------------+---------------------+
+| Internal flashing | Yes                 |
++-------------------+---------------------+
+```
+
+The flash is divided into the following regions, as obtained with
+`ifdtool -f rom.layout backup.rom`:
+```
+00000000:00001fff fd
+00100000:001fffff bios
+00006000:000fffff me
+00002000:00005fff gbe
+```
+
+In general, flashing is possible internally and from an external header. It
+might be necessary to specify the chip type; `MX25L1605D/MX25L1608D/MX25L1673E`
+is the correct one, not `MX25L1605`.
+
+### Internal flashing
+
+Internal access to the flash chip is unrestricted. When installing coreboot,
+only the BIOS region should be updated by passing the `--ifd` and `-i bios`
+parameters to flashrom. A full backup is advisable.
+
+Here is an example:
+
+```
+$ sudo flashrom \
+  -p internal \
+  -c "MX25L1605D/MX25L1608D/MX25L1673E" \
+  -r backup.rom
+$ sudo flashrom \
+  -p internal \
+  -c "MX25L1605D/MX25L1608D/MX25L1673E" \
+  --ifd -i bios \
+  -w coreboot.rom
+```
+
+```eval_rst
+In addition to the information here, please see the
+:doc:`../../flash_tutorial/index`.
+```
+
+### External flashing
+
+The SPI flash chip on this board can be flashed externally through the
+SPI_ROM1 header while the board is off and disconnected from power. There
+seems to be a diode that prevents the external programmer from powering the
+whole board.
+
+The signal assigment on the header is identical to the pinout of the flash
+chip. The pinout diagram below is valid when the PCI slots are on the left
+and the CPU is on the right. Note that HOLD# and WP# must be pulled high
+(to VCC) to be able to flash the chip.
+
+                +---+---+
+     SPI_CSn <- | x | x | -> VCC
+                +---+---+
+    SPI_MISO <- | x | x | -> HOLDn
+                +---+---+
+         WPn <- | x | x | -> SPI_CLK
+                +---+---+
+         GND <- | x | x | -> SPI_MOSI
+                +---+---+
+
+## Intel Management Engine
+
+The Intel Management Engine (ME) can be disabled by setting the ME_DISABLE
+jumper on the board. It pulls GPIO33 on the ICH10 low, causing the "Flash
+Descriptor Security Override Strap" to be set. This disables the ME and also
+disables any read/write restrictions to the flash chip that may be set in the
+Intel Flash Descriptor (IFD) (none on this board). Note that changing this
+jumper only comes into effect when starting the board from a shutdown or
+suspend state, not during normal operation.
+
+To completely remove the ME blob from the flash image and to decrease the size
+of the ME region, thus increasing the size of the BIOS region, `me_cleaner` can
+be used with the `-t`, `-r` and `-S` options.
+
+## Fan control
+
+There are two fan connectors that can be controlled individually. CPU_FAN
+can only control a fan by a PWM signal and SYS_FAN only by voltage. See
+the mainboard's `devicetree.cb` file for how coreboot configures the Super
+I/O to control the fans.
+
+## Variants
+
+Various similar mainboards exist, like the Acer Q45T-AM. During a discussion
+in #coreboot on IRC, ECS was suspected to be the original designer of this
+series of mainboards. They have similar models such as the ECS G43T-WM.
diff --git a/Documentation/mainboard/index.md b/Documentation/mainboard/index.md
index fc602de1a98f..67af86f058c2 100644
--- a/Documentation/mainboard/index.md
+++ b/Documentation/mainboard/index.md
@@ -6,6 +6,10 @@ This section contains documentation about coreboot on specific mainboards.
 
 - [X210](51nb/x210.md)
 
+## Acer
+
+- [G43T-AM3](acer/g43t-am3.md)
+
 ## AMD
 - [padmelon](amd/padmelon/padmelon.md)