Hardware and Software Design • Manufacturing Services
page 23
or 5,6,7 will result in an error. The hardware will terminate the operation without doing any transfers and set the
done bits for channels 1,2,3 [5,6,7]. Normally only channel 0 or 4 will have the done bit set.
The start bit is read/writeable and resettable. The start bit will, once the SDRAM is initialized and the FIFO is
ready, start a transfer or keep one going. The hardware, when the length condition is satisfied, will reset the start
bit. 1 = set. If the software resets the start bit prematurely during operation, the current mode is aborted at the
next logical opportunity. If a channel is aborted, the done bit is set and the input FIFO is emptied. In capture mode,
this data will be written to the SDRAM if the programmed length has not been reached. If the programmed length
has still not been achieved, the last word in the FIFO will be repeatedly written to the SDRAM until the desired
length has been satisfied. The X_TOTALx_RDBK register can be read to determine the number of valid samples
that were written for channel x.
When DIR = 0 the IO bit selects Capture or Retrieve mode of operation. 1 = Capture data from the de-serializer
into SDRAM. 0 = Retrieve data from SDRAM to the PCI bus. In capture mode any number of channels can be
enabled and any combination of addresses and lengths. In Retrieve mode only channel 0 or Channel 4 should be
active. Point the start address at the first channel of interest, set the length and start Retrieve mode. When the
data read is completed move the start pointer to the next selection and start channel 0 Retrieve again. The length
register does not need to be updated unless a different length is desired.
In capture mode the channels can be started in any order. The state machine revisits the selections periodically
and new channels will be added into the processing at that time.
DIR when 1 selects Direct mode. In Direct mode the SDRAM is bypassed with the data flowing from the Input to
the Output FIFO. The channel is selected with the start bit active – ONE channel ONLY in this mode. In Direct
mode there is no count associated with the transfer. Run until software turns off the start bit and the pipeline
empties. Alternatively the FE software done bit can be set to cause the operation to terminate by emptying the
Input FIFO.
Load when ‘0’ pre-loads the address stored in the Start register into the address counter for the channel in
question when that channel is first accessed for a Capture transfer. If set to ‘1’ then the address is not preloaded
and will continue on from whatever was programmed [or not!] previously. It is important to pre-load the initial