FIFO mode is used to record signal data continuously to or from the PC memory (RAM) and hence onto the hard disk. It has a cost advantage as PC RAM and drives are of a relatively low cost. Below is a description of the mode, we will concentrate on signal capture data, but the operation with signal generation cards is much the same but in the opposite direction
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Method: During data transfer the whole of Spectrum M2i / M3i cards on-board memory is available as a transfer FIFO buffer ensuring reliable data movement, automatically controlled from the driver for best performance. In a continuous operation a section of this transfer ("FIFO") buffer is emptied to the PC whilst another section is filled by the card. This operation can work alongside the processing the data in your software application. Transfer starts with a trigger event, running until the user stop command, or until user defined number sample segments have been collected. Utilising the scatter-gather DMA technique transfer rates are dependent on PC component performance and the type of slot the card is plugged into. The rates illustrated in the diagram above are for capture into PC RAM and achievable by many PC's.
Real-time capture to SATA hard disk drive has the great advantage of storage space and works well with for most applications, but note that it is slower than PC RAM, with on average only a 40MBytes/sec read speed, (older IDE drives can only work at around half this rate!) With signal capture operations, any signal data the hard disk cannot deal with is temporarily stored in PC RAM, but this can result in data backing-up, filling the PC RAM then the cards own memory in extreme cases, resulting in a data over-run message, at which point the Spectrum card driver will stop the card. Note that with signal generator cards the overrun process will not occur where data starts from the hard disk, as this is the slowest component in the data transfer chain. For more information about increasing read/write speed to hard disk drives click here for more information on RAID systems.
FIFO mode may be combined with options such as Multiple Recording / Replay for greater capture control, this way data is only captured (or generated) when an event of interest comes along, thus making best use of the available PC's PCI/PCI Express bus bandwidth. Fifo mode works under Linux or Windows. The amount of PC RAM available under 32 bit Windows is limited to about 3.2 Gbytes, (4 Gbytes can be fitted into the PC but some space is always required for the operating system). These limits do not apply Windows 64 bit and the user can fit as much memory as the motherboard can hold!
A final important note! If you wish to capture or generate signals for longer periods at greater rates than the PC will handle, then consider upgrading the cards considerable on-board memory, up to 4GBytes are available as an option.