DIRECT-TO-DISK (DDisk) OPERATION:
DIRECT-TO-DISK RECORDING (DDisk):In order to use this, you must be in RTime mode. If the Direct or Cache Write option is active, then when you hit DDisk (unshifted D-key) you will be prompted for the name of a file to receive the data. You may accept the default with ENTER, enter another directly, or use the File Access system to replace an existing file or review names. You will be asked for overwrite confirmation of any file that already exists.If you specify drive A: or B:, the DDisk option will exit with an Alert and the message:
'No DDisk recording to floppy drives.'
This is because floppy drives are just too slow for the fast recording for which the DDisk option is designed. Recording begins immediately after the file name is accepted. Alternatively, if the Memory Write mode is selected, the recording will start immediately upon hitting the D-key. You won't be prompted for a file name until the recording ends, and then you have the option of saving to any drive, including a floppy, or aborting via the ESC key and confirm prompt. You may end the recording at any time by turning off DDisk with the same D-key. While the recording is in progress, certain key options and menu items will be disabled to avoid interference with the recording process. The Stimulus Generator can not be changed during DDisk operation: The cursor will be prevented from moving to the output controls, and while you may bring up the individual output control submenus, the cursor will be missing from these so you can't change any settings. No Help system access is available during recording, to prevent contention for the disk drive.
DDISK CONTROL MENU:The DDisk Control menu (CTRL-D) allows control of several parameters. There are separate pages of this menu for DDISK WRITE and DDISK READ functions. If CTRL-D brings up the READ menu, use CTRL-PgUp or CTRL-PgDn to flip to the WRITE menu. Except for the Readout Units, the WRITE options must be set BEFORE you start the recording... once DDisk recording starts, the menu cursor will skip over them to prevent changes. The small double-headed vertical arrow indicator near the top right of the menu will also disappear to show that you can not use CTRL-Pg keys to see the DDISK READ menu while recording is in progress.When reading a DDisk file with DskRd (ALT-D), the DDISK READ menu will similarly have the double-arrow indicator removed to show that you can't go to the DDISK WRITE menu until you have hit ALT-D again to toggle DskRd off. All options in the DDISK READ menu are accessible.
DDISK PRESET FILE SIZE:You can preset the size of the file to be recorded, so that you don't have to have quick reflexes to shut of the recording at the desired size (or time) when you are recording at high speeds, or if you just want all recordings the same size. Enter the file size desired in KBytes, which includes only the size of the data portion of the file. (NOTE: A KByte is 1024 bytes, not 1000.) Daqarta will also add 214 bytes of format information.The number of data bytes per second will be the sample rate times the sample size in bytes, which will be 1 for 8-bit boards or 2 for 12- and 16-bit boards. (At present, Daqarta only supports mono recording.) So for a 12-bit board running at 40 kHz, the recording would use 80000 bytes per second, or 80000/1024 = 78.125 KBytes. Note that if you use a Key Macro to record a Preset DDisk file, you may want to have the macro wait until the end of the recording before proceeding with the remainder of the macro commands. To do this, you must manually toggle the DDisk operation off with the D-key when you are recording the macro, instead of waiting for the Preset end. (With very short Preset sizes, you may need to temporarily increase the size to give yourself time to hit the key manually before the Preset ends.) The macro handler will note that a Preset DDisk recording was in process and will store a special code instead of the actual D-key. Then later, when the macro is running, that code will be interpreted as "wait for the end of the Preset DDisk". You can't use WaitP here to wait for the Pause at the end of the DDisk recording, because a DDisk Pause is actually a special state that only stops the display updates, but not the recording process. One application that uses Preset DDisk in a Key Macro is described in detail under Sound-Triggered Recording. DDISK PRESTART:Sometimes the event you want to record is not completely under experimental control, and may start at an unpredictable time. If the required sample rate is too fast to just let the recording run while you wait for the event to happen, you may be stuck with your finger hovering over the ENTER key, waiting for the subject to sneeze or whatever. But what about your reaction time... how could you ever get the start of the event?That's what Prestart is for: It allows a "hedge" of up to 15000 samples (30000 for 8-bit boards) that happened before you hit the key. This works because in RTime mode we are continually taking samples into a large recirculating buffer. When the normal start command is received, Daqarta notes the next sample number to determine where to start dumping data to the the disk. With Prestart, we are simply telling it to start the dump from a prior sample. Of course, for this to work we must actually have those samples in the buffer, which merely means that RTime mode must have been active (not Paused) for this long before the recording starts.
DDISK READOUT UNITS:Once recording starts, a DDisk Position Readout box will appear to the right of the Cursor Readout box below the trace area. This shows the file position at the start of the current trace. Readout Units may be toggled between bytes, time in seconds, or time in HH:MM:SS format by successive hits of ENTER with the cursor at this item. The units may be changed at any time during a recording.The readout is updated once per sweep. In DDisk Pause mode, where the display is frozen and there are no proper "sweeps" while data collection proceeds, the readout shows the current data point being collected instead of the trace start. The readout will thus update much more rapidly. In Spectrogram mode this readout shows the file position of data currently being processed, and thus is updated at each horizontal time increment. An additional readout box is also displayed at the left end of the trace area to show the file position at the start of the screen. This readout is updated once per screen sweep. If you begin the DDisk recording while in Spectrogram mode, the sweep will restart at the left end of the trace area so that the start readout will be correct. However, if you are using Prestart you presumably are interested in those points just before you hit the key, so in that case the Spectrogram sweep is NOT reset. Instead, the start readout shows the Prestart value, preceded by '>' to indicate that it does not really refer to the left end of the trace, but the point where you initiated the DDisk recording.
DDISK REMOTE:Most boards with digital input capability can allow the DDisk recording to be controlled by a TTL level. If your experiment can provide this level only during the events of interest, you can greatly reduce not only wasted disk space, but also the wasted time spent searching for events in an otherwise long and uneventful recording.Also, many experiments may require operator intervention at the site of the experiment, which may not be all that close to the computer keyboard. The experiment may take place in a shielded and/or soundproof room, with the computer outside to minimize electrical and acoustic noise.
CAUTION: Do not connect any electrical equipment to a living subject without proper signal isolation techniques. A lethal shock could result.
See REMOTE CONTROL SWITCH CONSTRUCTION for construction and wiring details of a simple hand-help switch. The Remote Control item in the DDisk Control menu must be active (reverse-color Yes) to enable the remote control. This is just a safety precaution and a convenience, in case you DON'T want the control to be used but someone flipped the switch at the experiment location. Note that Daqarta allows boards which don't normally have digital inputs, such as sound cards, to use a printer port for remote control.
DDISK SKIP:The Spacebar key performs a keyboard equivalent of the remote control. You can use this to temporarily suspend recording if you detect some transitory problem, like your subject has a momentary fit of giggling during brainwave recording, or the kitten has decided it is more interested in something other than your elaborate display for evoking visual responses, or passing trucks interfere with your field recording of frog mating calls, or birds land on the loudspeaker you are testing outdoors since you don't have an anechoic chamber.CAUTION: Do not connect any electrical equipment to a living subject without proper signal isolation techniques. A lethal shock could result.
DDISK PAUSE:When you hit Pause (or an average is Done, etc) while in DDisk record mode, only the display is frozen... data collection and saving to disk continues unchanged.The difference between Skip and Pause is that in Skip, the trace is still active, so you can see when conditions are again suitable to resume recording. With Pause, the display is frozen and you would need to tell via other means. You would typically use Pause to momentarily examine some detail of the trace without disturbing the recording, then when you are sure the reaction is NOT going critical you would unPause to resume viewing the incoming data.
DDISK WRITE MODE - DIRECT:This is probably the best choice for extended DDisk recording. In this mode the cache (if present) is "flushed" to disk and disabled for the duration of the recording, and Daqarta will send data directly to the disk whenever it accumulates 32 KBytes of samples... for example, once every second with 16-bit data and a sample rate of 16384 samples per second.This mode, unlike the following Memory mode, allows recordings limited only by the size of the drive. It is a little slower to activate, since it requires a file name before the DDisk recording begins.
DDISK WRITE MODE - MEMORY:For recording files that will fit into memory, this mode is usually better than the above Direct mode. The recording starts as soon as you hit the DDisk D-key, and sends all the data to memory. You are only prompted for a file name after the recoding ends, at which point you may optionally elect to discard the data via the ESC key and confirmation prompt.In order to use this mode, your CONFIG.SYS file must include HIMEM.SYS to make extended memory available to DOS. If Daqarta doesn't find the eXtended Memory System (XMS) present on start-up, the Memory option will not be available. Since files using this mode can be no larger than the amount of XMS memory present, that limiting value will appear as a Preset file size unless you set something smaller. To gain maximum XMS memory, you may wish to remove SMARTDRV.SYS from your CONFIG.SYS file (or SMARTDRV.EXE from AUTOEXEC.BAT). Also note that if you run Daqarta after temporarily exiting to the DOS prompt from some other DOS program, that program may be holding onto XMS memory that won't be available here. Further, any Play files loaded into the the STIM3A Advanced Stimulus Signal Generator will also take up XMS memory. Besides quicker starts of the DDisk process, another big advantage is that writing to memory is much faster than writing to a disk, which may allow higher sample rates if you are using a non-DMA lab-type board instead of a sound card. Finally, since the file is not actually saved to disk until after the recording is complete, you can elect to save it to a floppy disk instead of the hard drive.
DDISK WRITE MODE - CACHE:A disk cache attempts to speed hard drive access by putting a memory buffer between the operating system and the physical disk. The idea is that since many programs tend to read and write the same data repeatedly, it will be faster to get that data from memory than from the relatively slower disk. When a program attempts to write to the disk, the cache controller secretly squirrels the data away in its memory buffer and doesn't write anything, on the assumption that this data will need to be read soon anyway. If the program tries to write a LOT of data to the disk, the buffer will eventually fill up and the controller will flush some it to the real disk.A large cache can thus greatly prolong the time between real disk accesses during DDisk operation, which could provoke a power management system to shut down the drive. For this reason, you may want to avoid the Cache option in the DDISK WRITE menu. Instead, use the default Direct option for extended recording, or the quicker Memory option for Preset file sizes that will fit into memory. When the recording ends, normal cache operation will be automatically restored... the OFF option only refers to the state of the cache during the actual DDisk recording. All other file operations will always use the cache, regardless of this setting. Daqarta can control disk caches that conform to the DOS SMARTDRV interface specifications, version 3.00 and greater. If Daqarta doesn't detect this type of cache when it starts up, the Cache option will not be available in the DDISK WRITE menu. If you are using some other type of cache, it will not be disabled during DDisk recording. SMARTDRV is loaded by including a SMARTDRV.EXE line in your AUTOEXEC.BAT file or a DEVICE=SMARTDRV.SYS line in your CONFIG.SYS file. (The proper DOS path must also be supplied... see your DOS manual.)
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