Documentation: Add Asus P3B-F

Change-Id: I0cd6141bb8baa082d5558490533649f907f25dd1
Signed-off-by: Keith Hui <buurin@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61538
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

Documentation/mainboard/asus/p3b-f.md

@@ -0,0 +1,106 @@
+# ASUS P3B-F
+
+This page describes how to run coreboot on the ASUS P3B-F mainboard.
+
+## Flashing coreboot
+
+```eval_rst
++---------------------+---------------------------+
+| Type                | Value                     |
++=====================+===========================+
+| Model               | SST 39SF020A (or similar) |
++---------------------+---------------------------+
+| Protocol            | Parallel                  |
++---------------------+---------------------------+
+| Size                | 256 KiB                   |
++---------------------+---------------------------+
+| Package             | DIP-32                    |
++---------------------+---------------------------+
+| Socketed            | yes                       |
++---------------------+---------------------------+
+| Write protection    | See below                 |
++---------------------+---------------------------+
+| Internal flashing   | yes                       |
++---------------------+---------------------------+
+```
+
+flashrom supports this mainboard since commit c7e9a6e15153684672bbadd1fc6baed8247ba0f6.
+If you are using older versions of flashrom, below has to be done (with ACPI disabled!)
+before flashrom can detect the flash chip:
+
+```bash
+  #  rmmod w83781d
+  #  modprobe i2c-dev
+  #  i2cset 0 0x48 0x80 0x80
+```
+
+Upon power up, flash chip is inaccessible until flashrom has been run once.
+Since flashrom does not support reversing board enabling steps,
+once it detects the flash chip, there will be no write protection until
+the next power cycle.
+
+### CPU microcode considerations
+
+By default, this board includes microcode updates for 5 families of Intel CPUs
+because of the wide variety of CPUs the board supports, directly or with an
+adapter. These take up a third of the total flash space leaving only 20kB free
+in the final cbfs image. It may be necessary to build a custom microcode update
+file by manually concatenating files in 3rdparty/intel-microcode/intel-ucode
+for only CPU models that the board will actually be run with.
+
+## Working
+
+- Slot 1 and Socket 370 CPUs and their L1/L2 caches
+- PS/2 keyboard with SeaBIOS (See [Known issues])
+- IDE hard drives
+- USB
+- PCI add-on cards
+- AGP graphics cards
+- Serial ports 1 and 2
+- Reboot
+
+## Known issues
+
+- PS/2 keyboard may not be usable until Linux has completely booted. With SeaBIOS
+  as payload, setting keyboard initialization timeout to 2500ms may help.
+
+- The coreboot+SeaBIOS combination boots so quickly some IDE hard drives are not
+  yet ready by the time SeaBIOS attempts to boot from them.
+
+- i440BX does not support 256Mbit RAM modules. If installed, coreboot
+  will attempt to initialize them at half their capacity anyway
+  whereas vendor firmware will not boot at all.
+
+- ECC memory can be used, but ECC support is still pending.
+
+## Untested
+
+- Floppy
+- Parallel port
+- EDO memory
+- ECC memory
+- Infrared
+- PC speaker
+
+## Not working
+
+- ACPI (Support is currently [under gerrit review](https://review.coreboot.org/c/coreboot/+/41098))
+
+## Technology
+
+```eval_rst
++------------------+--------------------------------------------------+
+| Northbridge      | :doc:`../../northbridge/intel/i440bx/index`      |
++------------------+--------------------------------------------------+
+| Southbridge      | i82371eb                                         |
++------------------+--------------------------------------------------+
+| CPU              | P6 family for Slot 1 and Socket 370              |
+|                  | (all models from model_63x to model_6bx)         |
++------------------+--------------------------------------------------+
+| Super I/O        | winbond/w83977tf                                 |
++------------------+--------------------------------------------------+
+```
+
+## Extra resources
+
+[flashrom]: https://flashrom.org/Flashrom