From 5cc75f5efe0d27abb427bb46e14372c6d2161edd Mon Sep 17 00:00:00 2001 From: Frank Mori Hess Date: Tue, 8 Jul 2003 23:51:29 +0000 Subject: [PATCH] fix regressions, remove obsolete description of isapnp support --- doc/install.sgml | 64 ++++++++++++++-------------------------------- doc/other.sgml | 32 ++++++++++++++++++++++- doc/reference.sgml | 2 +- 3 files changed, 51 insertions(+), 47 deletions(-) diff --git a/doc/install.sgml b/doc/install.sgml index bbcb581..897af20 100644 --- a/doc/install.sgml +++ b/doc/install.sgml @@ -27,76 +27,50 @@ the comedi_config command. (As root of course.) Here is an example of how to use the command (perhaps you should read its man page now): -/usr/sbin/comedi_config /dev/comedi0 ni_atmio 0x260,3 +PATH=/sbin:/usr/sbin:/usr/local/sbin:$PATH +comedi_config /dev/comedi0 labpc-1200 0x260,3 This command says that the “file” /dev/comedi0 can be used to access the &comedi; -device that uses the ni_atmio driver, and that +device that uses the labpc-1200 board, and that you give it two run-time parameters (0x260 and 3). More parameters are possible, for example to discriminate between two or more identical cards in your system. If you want to have the board configured in this way every time you -boot, put the line above into a start-up script file of your Linux +boot, put the lines above into a start-up script file of your Linux system (for example, the -/etc/rc.d/rc.local file), or in the system-wide -&comedi; configuration file /etc/comedi.conf. -You can, of course, also run this command at a command prompt. +/etc/rc.d/rc.local file), or for PCMCIA +boards the appropriate place is the /etc/pcmcia/comedi script. +For non-PCMCIA boards, you can also arrange to have your driver +loaded and comedi_config run with by adding a few lines +to /etc/modules.conf (see the INSTALL file for the comedi +kernel modules). You can, of course, also run comedi_config +at a command prompt. This tutorial goes through the process of configuring &comedi; for two devices, a -National Instruments AT-MIO-16E-10 (which has the -driver mentioned above), and a +National Instruments AT-MIO-16E-10, and a Data Translation DT2821-F-8DI. -The NI board is plug-and-play, and the man page -tells you that you need to configure the PnP part of the board with -isapnptools. The isapnptools -package is a little cryptic, but the concepts are simple. Once you've -learned how to use it, you can settle on a -/etc/isapnp.conf file such as this: - - +The NI board is plug-and-play. The current ni_atmio driver +has kernel-level ISAPNP support, which is used by default +if you do not specify a base address. So you could simply +run comedi_config as -# ANSI string -->National Instruments, AT-MIO-16E-10<-- -(CONFIGURE NIC2400/10725401 (LD 0 - (IO 0 (BASE 0x0260)) - (INT 0 (IRQ 3 (MODE +E))) -# (DMA 0 (CHANNEL 5)) -# (DMA 1 (CHANNEL 6)) - (ACT Y) -)) +comedi_config /dev/comedi0 ni_atmio - - -(This file also contains a few lines about overall configuration and -about the sound card that happens to be in the same computer.) -Currently, the driver doesn't use DMA, but it may in the future, so -the DMA lines are commented out. It has been reported that the -National Instruments board does not always work with interrupts other -than IRQ 3, and that the device ignores the IRQ and DMA information -given here. However, keep the information here to remind yourself that -the numbers aren't arbitrary. - - -The man page -explains that the option list is supposed to be -“(I/O base),(IRQ)”, so use the same -numbers as in /etc/isapnp.conf, i.e., -0x260,3. - - For the Data Translation board, you need to have a list of the jumper settings; these are given in the &comedi; manual section about this card. (Check first to see whether they are still -correct!) +correct!) The card discussed her is a DT2821-f-8di. The man page of comedi_config tells you that you need to know the I/O base, IRQ, DMA 1, DMA 2. However, @@ -131,7 +105,7 @@ So, the appropriate options list is: and the full configuration command is: -/usr/sbin/comedi_config /dev/comedi1 dt2821-f-8di 0x200,4,,1,1,1 +comedi_config /dev/comedi1 dt2821-f-8di 0x200,4,,1,1,1 The differential/single-ended number is left blank, since the driver already knowns (from the board name), that it is diff --git a/doc/other.sgml b/doc/other.sgml index 9644ebd..dfee185 100644 --- a/doc/other.sgml +++ b/doc/other.sgml @@ -998,7 +998,37 @@ data structure, and has no function at present. - +
+ +Anti-aliasing + + +If you wish to aquire accurate waveforms, it is vital that you use an +anti-alias filter. An anti-alias filter is a low-pass filter used to +remove all frequencies higher than the Nyquist frequency (half your sampling rate) +from your analog input signal +before you convert it to digital. If you fail to filter your input signal, +any high frequency components in the original analog signal will create +artifacts in your recorded digital waveform that cannot be corrected. + + +For example, suppose you are sampling an analog input channel at a rate of +1000 Hz. If you were to apply a 900 Hz sine wave to the input, you +would find that your +sampling rate is not high enough to faithfully record the 900 Hz input, +since it is above your Nyquist frequency of 500 Hz. Instead, what you +will see in your recorded digital waveform is a 100 Hz sine wave! If you +don't use an anti-alias filter, it is impossible to tell whether the 100 +Hz sine wave you see in your digital signal was really produced by a +100 Hz input signal, or a 900 Hz signal aliased to 100 Hz, or a 1100 Hz +signal, etc. + + +In practice, the cutoff frequency for the anti-alias filter is usually +set 10% to 20% below the Nyquist frequency due to fact that real filters +do not have infinitely sharp cutoffs. + +
diff --git a/doc/reference.sgml b/doc/reference.sgml index 653ed9a..3552a7a 100644 --- a/doc/reference.sgml +++ b/doc/reference.sgml @@ -1,4 +1,4 @@ - +
-- 2.26.2