7. Compactflash Comments

• Once formatted with a Fat16 partition for EPOC and an ext2 partition for linux, EPOC will see only the Fat16 partition (the D: drive). Linux will see and access both partitions, just as the case for Windoze; the /etc/fstab file gives the name of the Fat16 partition, of course. With such partitions, the psion effectively becomes a dual boot system. If you want to run EPOC applications as well, then be sure to format enough space (32MB?) to allow for saving those applications on the D: disk.


• The main Psion website states that there is a limit to the size of compactflash disk that can go into a Psion 5MX (20MB, I believe). This seems to be untrue - disks of up to 512MB have been used successfully.


• At one point I was told that I might save space using a JFFS2 filesystem, rather than ext2. However, I ran across an e-mail archive that had a message from the author of JFFS2 to the effect that compactflash cards are for all intents and purposes IDE devices, and ext2 was the way to go. Treat them like an ordinary IDE disk. Compactflash disks can be written on about 100,000 times before they give out, but these cards are also smart enough to distribute/rotate writing on them so as not to "wear out" particular spots. [If you do a little math you will find that it will take a long, long time to make enough writes to wear out a compactflash card.]


• Compactflash and swap space. Because compactflash disks can be written on about 100,000 times before they give out, one generally does not want to use swap space, and I add the "noatime" option when mounting the disk to ensure that the access times are not constantly written to the disk. It would seem to be worthwhile making some swap space, if you had a large disk, that you could enable from time to time should you need it. On the other hand, if you really needed swap space you could just make a file for it.


• Most compactflash disks should work in the psion, but drives of size greater than 512MB are as yet untested. Also be aware that some disks work better than others, others are flakey, and some of them are faster than others; "your mileage will vary". Some cards won't work at all. A benchmarks table is given below, and check out the DiskBench page (there are others around, e.g. for cameras and write time for photos) for a list of results and a utility to test the speed of your disk. It is not always true that you get what you pay for in this case (IMHO) - price seems to bear little resemblance to performance. It is worth searching the web for a few minutes for reviews of compactflash cards before purchasing. If you want to have a fairly complete system with picoGUI or X-windows (when either of them becomes more functional) and compilers, and still have disk space to work in, a 128 MB disk is recommended. As of this writing (March 2002) disk of 128 MB size could be bought for around US$50.


• It is worth getting a pcmcia compactflash reader (US$10) or other USB reader (US$20) for formatting and copying information directly to the compactflash card - these cards are as fast as UDMA33 IDE drives, so writing directly to them is WAY faster than trickling over the information on the 115200 baud serial line. Disks in pcmcia are recognized as IDE drives (/dev/hde), while disks in USB are recognized as SCSI disks (see your /var/log/messages file after you plug it into your notebook/desktop to see which disk it is).


• Currently the compactflash card must be in the socket when you boot, and must not be removed while running. The current driver does not support hot-plugging the card.


• I've been informed that the IBM microdrives do not fit into the Psion 5MX, nor do they work. You can read about the sad, if courageous, tale HERE. One hypothesis is that the microdrives do not work (after prying open your psion to cram it in) because the psions may not supply enough power to run them. Some lunatics have suggested powering them externally, but we'll leave that as a rainy day project... :)



COMPACTFLASH BENCHMARKS

We now have a standing request for additional compactflash benchmarks on your
Psion, and whether the compactflash card worked at all - post your results on
the PsiLinux mail list for now.

To test the write speed of your disk, use this shell script to write a 10MB file:

%%%%%%%%%%%%%%%%%%%%%%%%%%
#!/bin/sh
#
# Writes a 10MB file called "dump"
#
dd if=/dev/zero of=dump bs=1k count=10k && sync
%%%%%%%%%%%%%%%%%%%%%%%%%%

First execute "hdparm -u1 /dev/hda" which keeps the clock from slowing down with writes to the CompactFlash. The -u1 enables the unmaskirq option for the IDE driver, so the timer does not miss interrupts during the writes. Then run:


  sync && time ./writetest.sh
  rm dump

Comparing the laptop and Psion 5MX benchmarks below, we can see that either the
Psion has some room for improvement, or not all cards conform to the compactflash
standard the same way. Testing with file sizes over 1MB currently causes roughly
one lost interrupt for each MB written on Psion on the Sandisk 96MB card, so that's
why writes on it are so much lower. This does not happen on the faster 32MB card,
and that's why it's values are closer to the laptop values. The cause of the lost
interrupts is unknown, there are no available documents for ETNA.

The times given are the result of the "time" command; this result is flawed in that it severely underestimates the actual time of execution for technical reasons. It is a number, however, and at least the table below verifies some cards that are known to work in the machines. It also shows that the speed of these cards varies widely.


CARD	SIZE	DEVICE	TIME (approx)	MB/s	Notes
Sandisk	32MB	Psion 5MX PRO	27s	0.37MB/s
Lexar	???				Some of these work, and some do not work in Psion
PNY	64MB	Psion5MX
Sandisk	96MB	Psion 5MX PRO	119s	0.08MB/s
SanDisk	128MB	Psion 5MX PRO		0.61MB/s
Viking	128MB	Psion5MX	10.5s	0.95MB/s
NCP	256MB	Psion5MX	10s	0.98MB/s
Transcend	512MB	Psion5MX		0.8MB/s


LAPTOPS


					alignment here
Lexar	16MB	Laptop..........	9s	1.11MB/s
Sandisk	32MB	Laptop	16s	0.63MB/s
SimpleTech	32MB	Laptop	20s	0.50MB/s
Sandisk	96MB	Laptop	24s	0.42MB/s
PQI	128MB	Laptop	22s	0.45MB/s
Viking	128MB	Laptop	8s	1.25MB/s