Each VXI card acquires data from each of its ADCs and transfers it to a VME module using a single 40Mhz. 4 bit serial data link. The VME module contains memory and links for from two to eight VXI cards dependent on the expected data rates.
The VME module is a PowerPC CPU card running LynxOS. The VXI card serial links connect to a mezzanine board, mounted on the VME module, containing a DSP (Digital Signal Processor), four link connections, memory, and a high speed bus ( PCI ) connection to the PowerPC, and VME.
The DSP is the Analog Devices ADSP21062, which includes six 40Mhz. 4 bit serial links in each chip. Input data from the links is stored in memory on the mezzanine board, translated by the DSP to histogram addresses, and transferred via the PCI bus to the PowerPC as 16k buffers. The transfer rate over the PCI bus for block transfers of this sort is 100Mbytes/sec.
To accommodate slow rate experiments all the input, and internal buffers will be flushed when no transfer to the PowerPC has occurred for 1 second. The buffers can be flushed by specific request from the experimental control software; typically when the experiment is stopped, and started. Memory required per channel: 8K data, 16 time frames = 512Kbytes.