Gage CompuScope 14100C, Hardware Manual And Driver Installation Manual

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Memory organization on CompuScopes (except for CS85GC) 21
Memory organization on CompuScopes (except for the CS85GC)
Please note: for memory organization on the CompuScope 85GC, please refer to the next section.
Memory architecture
CompuScope cards have high-speed on-board memory to store the digital data for the CompactPCI
TM
bus to
access it in post-processing mode.
Interface to the CompactPCI
TM
bus
In order to allow optimum data transfer rates from the CompuScope card memory to the PC memory, the
on-board RAM is mapped into the memory space of the CompactPCI
TM
bus.
The exact address at which this memory is mapped is determined by the CompactPCI
TM
Plug-n-Play BIOS. This
means that the user does not have to set any jumpers or switches to configure the CompuScope card—it really is
plug and play.
Bus Mastering mode
Full Bus Mastering capabilities are provided on CompuScope cards, allowing the fast data transfer to occur as a
result of a Direct Memory Access (DMA).
Software loads the start address, destination pointer and number of points to be transferred into the
CompactPCI
TM
bus controller on the CompuScope card and then asks the card to do a DMA transfer. The
CompactPCI
TM
bus mastering control circuitry takes over from this point and performs the transfer without any
CPU involvement.
Data storage
The data coming out of the A/D converters or digital input is stored in the on-board memory buffer, which is
configured as a circular buffer. A circular buffer is used to guarantee that the system will keep on capturing data
indefinitely until a trigger event is detected.
The sequence of events is as follows:
•
CompactPCI
TM
bus tells the CompuScope to start_capture using a register bit.
•
The CompuScope sets BUSY flag. CompactPCI
TM
bus is denied any further access to the on-board
memory.
•
The on-board memory counters initialize to ZERO and start counting up, thereby starting data storage at
memory address ZERO.
•
The system waits for a trigger event to occur while it is storing data in the on-board memory. This data is
called Pre-Trigger data.
•
Once the trigger event is received, a specified number of Post-Trigger points are captured. The number of
Post-Trigger Points can be specified by writing to a register on the CompuScope.
•
After storing the specified number of Post-Trigger Points subsequent to receiving the trigger event,
acquisition is stopped, BUSY flag is reset and PC bus is allowed access to the on-board memory.