HOWTO_setup_gentoo_on_a_pda_or_embled_system

Why gentoo on a PDA

PDAs are evolving

PDAs are evolving a lot (even more when they are in competition with ultra-light notebook/tablet-pcs with the Pentium-M processor.

Interesting ourselves in the PDA hardware is a necesary step because there are very different sorts of distributions, and optimisations due to very different systems.

nowadays there are 3 types of PDA (to be completed of course):

Types of PDAs

Slow and large HDD ones

I know one well because i've got one. There are some (go to linux devices to know about it but all aren't referenced) video/mp3 players on the move (I think the term "walkman" is inappropriate here) that run linux natively because the manufacturer used linux to power these devices. Their main caracteristics are:

The SOC (system on a chip):

• A slow CPU (Mine is a 150Hz ARM9 V4l)
• A coprocessor (for reading DivX, XviD)
• An MP3 decoder
• A lot of I/O (USB client, USB host, etc.)
• A huge HDD (i have 30 GB)
• I think a 320x240 screen in my case but it may vary a lot

Faster but with moderate space

There is the case of the Zaurus ones and a Palm i think that has a 4GB drive built-in

The Zaurus have the folowing caracteristics:

• 400MHz CPU
• 640x480 screen
• 4GB of internal HDD space
• Keyboard

Fastest but without storage

• 600MHz cpu
• NO internal hard drive
• 640x480 screens
• Sometimes has mmx, graphic accelerators, etc.

Other considerations

• some more space could be easily added with the following devices:
  • a compact-flash or sd card
    • be careful of the number of read-writes: the flash cards (cf, sd, mmc, etc.) have a limited number of read-write accesses. so there is a need for a RAM filesystem: the filesystem is stored on such cards and when the system boots it's decompressed and copied to ram so there is only one access after the boot
  • A Toshiba 5GB PCMCIA HDD
  • External storage (USB, WIFI-HDD, etc.)
    • Increase the space taken by the device
    • There are some cables (for example in the USB case)
    • Not anymore all in one concept (for USB HDD.)
• As it is the same linux kernel (in most but not all cases but there are kernel modules...) as with notebooks there is huge hardware support...as if it was a notebook... this is great for pcmcia cards for example. With open-source software and open-source drivers that offers a lot of possibilities (USB2.0, gigabit ethernet, PCMCIA, TV, etc.)
• the CPU speed has increased a lot and it has become as fast as some not so old systems

General guidelines

the advantages of using gentoo (or another desktop os) is that you can use all the desktop programs and so you have a great collection of software and you don't need to port this kind of software to another os as opie (that is more adapted to pda) =>this is true for libraries, console apps (if an adapted front-end is used) and graphics apps on 640x480 pda =>this is less true for graphic front-ends that need to be a little bit tweaked (sometimes there is only the configuration to change, sometimes a bigger work must be done... but there are programs such as kdesin (if my memory is good) that help on the design of graphic front-end or maybe scripts that change values on Xdialog for example (maybe don't exist but can easily be done))

processors

we need to identify the family of the processor in order to feed it with the binaries of its corresponding arch (personally i'm lost between arm and ppc with xcales and such processors)

space considerations

here space considerations is determining a type of linux-os

as we have seen before, space may vary a lot depending on the devices and it's accessories (compact-flash cards...) but also the way of using it... (flash cards...) so there is a lot of diferent installations with: ->embed based (such as gentoo derived from the familiar distributions) =>busybox for example is a bash (with all the base programs such as cp, ln...) that is designed to take as little space as possible with: -less automatic programs(true for chroot) -less help builtin -no manual -reduced functionalites such -v (verbose) -an all in one executable =>a tiny version of the X server

THE SETUP

• you will need to setup a cross-compiling environment if your processor architecture (Desktop computer) is different from the target (pda, embedded):

-if you have the same architecture this step is not needed, for example if you have a mac (ppc) and you have a ppc pda or embedded device

-if you have a different architecture the processor can't compile other's architecture binaries without cross compiling (as far as i know)

Compilations flags

using the -O3 flag is not a good idea, as it takes up a good deal of space. Using -O2 or -Os would probably be wiser.