Wiener VM-DBA, User Manual

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5.4 Guide to using the VME bus waveform storage and viewing facility
VM-DBA is capable of storing the states of 95 VME bus lines in 2048 consecutive time steps
at a rate of either 100 MS (mega samples per second) or 200 MS. The sampling rate is user-
programmable. The waveforms are stored in 3 32-bit wide FIFOs for the subsequent readout
either via the VME or the USB interface. The states of individual VME bus lines are
represented by bits of these 32-bit words with the following mapping:
(i) WVA : VME address bus lines A(1 to 31) are mapped in a natural order to bits of the
waveform address word WFA(1 to 31). When the waveform acquisition is active, the latter
words are stored in the Address FIFO at the base address of
0x100 .
(ii) WVD : VME data bus lines D(0 to 31) are mapped in a natural order onto bits of the
waveform data word WFD(0 to 31). When the waveform acquisition is active, the latter
words are stored in the Data FIFO at the base address of
0x200 .
(iii) WVC : Other 32 VME bus lines are mapped onto bits of the waveform control word
WFC in a way illustrated below. When the waveform acquisition is active, the latter words
are stored in the Control FIFO at the base address of
0x300 .
WFC 7 6 5 4 3 2 1 0
VME DTACK BERR AM5 AM4 AM3 AM2 AM1 AM0
WFC 15 14 13 12 11 10 9 8
WME IRQ3 IRQ2 IRQ1 AS DS1 DS0 NWR LWRD
WFC 23 22 21 20 19 18 17 16
VME BG1 BG0 IACKIN IACK IRQ7 IRQ6 IRQ5 IRQ4
WFC 31 30 29 28 27 26 25 24
VME BCLR BBSY BR3 BR2 BR1 BR0 BG3 BG2
The waveform acquisition proceeds as follows:
Upon the setup of the acquisition parameters and entering the acquisition regime, VM-DBA
writes the waveform words WFA, WFD, and WFC into their respective FIFOs configured for
a circular continuous operation. Thus, at any moment of time, these FIFOs store waveforms
in 2048 preceding time steps. Upon detection of the trigger signal parts of the FIFOs are
drained so as to preserve the desired number of pre-trigger steps, while the freed-up space is
filled with post-trigger waveforms, until the FIFOs are filled. Obviously, one cannot store
more than 2048 pre-trigger steps. When so desired, one may forgo not only all pre-trigger
steps, but also an additional 2048 steps, i.e., effectively commencing acquisition 2048 time
steps after the detection of the trigger signal.