Linux on the Webpal

This page describes what I did to run Linux on the Webpal.    

Flash Partitions

There are two version of flash SIMM on the Webpal, a 1MB flash (512K x 16) and a 2MB flash (512K x 32).  It's easy to tell the difference: the 1MB flash SIMM has only a single flash chip while the 2MB flash has two flash chips.   Most Webpals came with the 1MB flash.   Some 2MB systems are now showing up or with a careful hand, one can add a second flash chip to a 1MB SIMM to turn it into a 2MB flash SIMM.    I've done this myself by removing the flash chip from one SIMM board and adding it to a second SIMM board.   I use the ChipQuik® SMD removal kit #SMD1 to help make it possible to remove the SIMM chip without damaging it.   This kit contains  two very useful items, flux in a syringe and very low temperature solder.    The kit costs between $15-$20.    I bought mine at Digikey but I've seen it at Fry's stores in the San Francisco Bay area.

The starting offsets of the first three partitions are fixed -- they are hardcoded in the bootp program.   The starting offset of the
root partition can be moved.   This gives the ability to adjust the sizes of the zImage (kernel) and root partitions to meet a particular application's needs.   For example, one might want a larger kernel and use NFS for the  root partition.   In this case, the root partition start could be set to zero and the zImage partition would then be 992K.

If you have a SIMM with a 1MB, the flash is divided into the following partitions:
 
Partition Description
Starting Location
Length
bootstrap loader
0x00000
24K
parameters
0x06000
8K
zImage
0x08000
variable (default  = 608K )
 root
variable (default = 0xa0000 )
variable (default = 384K

If you have a SIMM with a 2MB flash, the flash is divided into the following partitions:
 
Partition Description
Starting Location
Length
bootstrap loader
0x00000
32K
parameters
0x08000
16K
zImage
0x0c000
variable (default = 592K)
 root
variable (default = 0xa0000 )
variable (default = 1408K)

As you can see, there is not much room to store a reasonably useful root partition on the 1MB flash.   For a 1MB flash system, most people either mount root via NFS or install some sort of IDE device as described below.   For 2MB flash systems, there is the possiblility of using the Webpal with only the onboard flash since the root partition is now over 1MB.

Here is a short description of the partitions:

Bootstrap loader (V3.3)

The bootstrap loader initializes the Webpal, copies the zImage from flash into RAM, and branches to it.  Status messages are output to either the video interface or serial port.   V3.3 supports both 1MB (16 bit wide) and 2MB (32 bit wide) flash.    A new wpflash program is required when using V3.x for flash programming.   The new wpflash program supports both V3.x or V2.x for flash programming.

By default, bootstrap messages are output to the VGA port and the parallel port is used to connect to a Linux system for flash programming.    If you wish to build a serial interface, you can use the serial port for both bootstrap messages and flash programming.   This is done using the serialbootp parameter as described in the parameters section.

Holding down the SW2 button inside the Webpal while resetting will cause the bootstrap to use the alternate device(s) used for output/programming.   For example, if normallythe serial port was used, holding down the SW2 button during reset would cause the webpal to use the video and parallel ports instead.

The bootstrap loader contains a flash programmer that can erase, program, and read any of the partitions on the flash.    A program called wpflash runs on another Linux system and communicates with the flash programmer via either the Webpal's serial or parallel port.   Use of the serial port requires the construction of the RS-232-C level adapter described elsewhere on this page.   Use of the parallel port requires a parallel Laplink cable which you can purchase at your local computer store.  Use of the parallel port also requires that your Linux system contains the parport driver, a driver that allows user level access to the low level parallel port routines in the kernel.

The bootstrap loader can detect both known versions of the Webpal CPU board and whether a 16 bit or 32 bit flash SIMM has been installed.   This information is displayed as the system boots.

If you program a 32 bit flash SIMM as a 16 bit flash, the bootstrap loader will still work.   However, if you then program the flash using the bootstrap loader, its will reprogram the flash in 32  bit mode.  This provides a method of bootstrapping 32 bit systems.    First, bring the bootstrap up as though the flash were 16 bits wide. Then, use the onboard programmer to reprogram it in 32 bit mode.

Bootstrap loader parameters

Data in the parameters partition controls the bootstrap loader behaviour.   The data consists of ASCII lines of text in the format:

name=value
The end of the parameters file is indicated by a NULL line (two or more NLs in a row)

Here are the parameters supported by the bootstrap loader:

If value is 1, bootstrap messages are sent to the serial port and the serial port is used for the flash programming.   If value is 0 or this parameter is not specificed, bootstrap messages are sent to the VGA screen and the parallel port is used for flash programming.   Holding down SW2 inside the Webpal while resetting will change negate the serialbootp value.
text is appended to the command argument passed to the kernel  (example: command=boot=/dev/mtdblock3 )
Defines the IDE parameters passed to the kernel (example: ide=0x170,0x376,11 ).  Generally, this parameter is not needed as the bootstrap loader will automatically configure the IDE interface to match the IDE parameters in the Linux Webpal port.
Defines the console parameters for the kernel (example: console= ttyS0,115200 )
Defines the parallel port parameters for the kernel (example:  parport=0x278,13 )
The root file system is mounted readonly.   Otherwise, the root file system is mounted read/write.
TV output is disabled, saving power and allowing the Webpal to run much cooler.  This is recommended unless you are using the TV outputs.   Note that setting tvoff does NOT disable the VGA outputs.    This option is required if you plan on using the IO pins for the RTC mod.
Specifies a new hexadecimal value for the starting offset of the root partition.  Since the zImage partition immediately precedes the root partition, this value also specifies the end of the zImage partition.   A value of zero means no root partition and the entire root partition space is added to the zImage partition.  The value must make a sector address in the flash.   This means that the address must be divisable by 0x10000 for a 1MB flash or 0x20000 for a 2MB flash.  During programming, the wpflash program read this parameter from the flash before programming and will take its setting into account when calculating a partition start and stop.     In addition, the bootp program passes all the partition information to the kernel using the 'Compaq' format.   If this option (Compaq bootldr partition table parsing in the Memeory Technology Devices (MTD) section) is specied during kernel configuration, then the kernel will correctly determine the starting offsets for the partitions.

Here are the pointers to the source code and a compiled binary of the bootstrap loader.
As an aid to getting started, I can program your flash with the bootstrap loader if you mail me your flash chip with return postage.   Please contact me at the email address below for more information.

Flash programming

To initially program the bootstrap loader into flash, I built a standalone flash programmer.     Both this standalone programmer and the programmer in the bootstrap communicate with a Linux system via either the serial or parallel port.    The program running on the Linux system is called wpflash. Here are short instructions for running the flash programmer: Start wpflash first and then press the reset button on the Webpal and programming should commence.   If you have problems synchronizing (this generally happen only in the parallel port mode), hold down the reset button, start the wpflash command, and then release the reset button.

Kernel Building

Here is a toolchain that can be used to build kernels on x86 linux systems.

The kernel patches are relative to the rmk patches on the ARM Linux site.    Apply these patches after you have applied the appropriate version of the rmk patches to the base kernel vesion.

The current Webpal patch is relative to:   Linux-2.4.18  and   2.4.18-rmk4 .

A sample config file and zImage:

 ( config )  ( zImage  )

Here are some kernel configuration options of note:

Root file system

For the root file system, there are several options: The Debian ARM distribution is a good source of precompiled binaries for building your root partition, either NFS or on an IDE device.   Of course, the usual popular embedded Linux packages like busybox and uClib can be used by compiling them for the ARM processor.

Here is a source of some binaries and source files.

Root file system on Compact Flash

I generally use a Compact Flash via an  IDE to Compact Flash Adapter.    I mounted the adapter under the main Webpal PC board on the bottom metal cover and then cut a slot in either the front or back panel so I can insert a Compact Flash card. Here is a picture showing the back panel version.

Due to a bug in the Webpal hardware, you need to pin that needs to be lifted to make the IDE interface work.

Root file system on 2.5 inch IDE notebook drive

A normal IDE drive can also be used.   2.5 inch drives are easier to use because they fit into the available space and only require +5V.   You can steal the +5V from the existing 5V regulator, although it will run hotter.   You'll need some sort of adapter between the larger 40 pin adapter and the 44 pin connector on the 2.5 inch drive.   There is about 11/16 of an inch clearance if you decide to mount the disk inside the unit, so be sure to use a 12mm or thinner drive.  Here are some pictures of adding a disk to the webpal:

Root file system on onboard flash

To use the root partition on the onboard flash, your root image must fit in 384K with a 1MB system.   This means probably only a few applications and maybe busybox.

Ethernet boards

I've replaced the serial modem with an NE2000-clone ethernet card.    Due to restrictions in the ISA bus interface on the Webpal, experience has shown that only ISA ethernet boards based on the Realtek 8019(AS) chip seem to work.   An example of such a card is the Kingston KNE20T.

The current kernel supports ISA PNP if enabled during kernel configuration.   This allows you to use the ISA PNP ethernet cards without having to set the card to non-PNP using its DOS utility.

If you wish to run a kernel without ISA PNP enabled, then you will need to set the ethernet card to 0x300 and make sure it is set to use IRQ3 since that's the only interrupt line wired to the ISA bus slot.    This maps to interrupt #9 in ARM linux.

The ne driver should work either compiled into the kernel or as a loadable module.

On a non-PNP system, load the driver with these two commands:

    insmod 8390
    insmod ne io=0x80400300 irq=0x09

For a PNP system, use:

    insmod 8390
    insmod ne

Serial Port

I built a RS-232-C serial port adapter to use the sytem without a display in various server applications.

Be sure to cut JP1.   If you don't, the IR receiver is also connected to this RS-232-C port and can cause garbage characters on the serial port.

IR keyboard / smart card slot

The current kernel patches support both the PS2 keyboard port or the IR keyboard.   There is a configuration option in the video driver section to enable/disable the IR keyboard.    If the IR keyboard is disabled, the serial path used by the IR keyboard appears as /dev/ttyS1.   This is useful if you wish to reprogram the AT89C52 for other purposes.

Based on my initial disassembly of the code in the AT89C52, it doesn't appear there is any smart card support.

Reprogramming the AT89C52

As supplied, the AT89C52 decodes IR keyboard input and sends it on a serial port to Linux.    Normally, this data goes to a keyboard driver in Linux.  However,  if the IR keyboard is disabled, the serial port data from the AT89C52 appears to Linux as /dev/ttyS1.

I use this option when I want to reprogram the AT89C52 microprocessor to do other things.   For example, I've reprogrammed the AT89C52 to decode wireless weather station signals from a small receiver and send the results via the serial port to the Webpal.   The application on Linux simply reads the data by opening /dev/ttyS1.  Many other possibilities exist to reprogram the AT89C52 for other tasks and have it communicate with Linux.  

Modem

If you are using the modem that came with the Webpal, it now appears to Linux as /dev/ttyS2.    This is a change from older kernels where it appeared at as /dev/ttyS1.


What works and what doesn't

The following devices seem to work: Not working (or not tested):

Other Webpal links

codeman's original bootstrap loader (for 2.2 kernels)
rscott's loader (including bootstrapping so you don't need a flash programmer -- but still requires a serial port)
justdave has an ftp site that contains some binaries and source packages for your root partition.
aswx has a schematic and lot of info on the Wepbal hardware.
tomw has a buildroot script.
luban has a 64K DRAM modification.


Last updated:  March 4 2005 by Bill Danielson ()