DOC E10523 Rev.D
Interactive Circuits And Systems Ltd. 2000
25
5.3 Performing Block Transfers
When performing block transfers, it is important that the transfer count is correctly
programmed. If not, memory buffer overflow may occur, or the ADC data window size may
be exceeded. The size of the transfer should be the size of the data block currently
available or the size of the ADC data window, whichever is smaller. For VME Master
transfers, the count is specified in (32 bit) longwords. Note that the VMEbus specification
limits block transfers to a maximum of 256 Bytes, however, the ICS-130 design does not
prevent transfers of larger blocks as described above.
5.3.1 VMEbus DMA Master
The SCV64 device controls all VMEbus Block transfers. These are also known as Direct
Memory Access (DMA) transfers. With A24 or A32 addressing, standard VMEbus Block
transfer (BLT) cycles may be used. With A32 or A64 addressing, Multiplexed Block transfer
(MBLT) cycles may be used.
The order of programming for Master BLT and MBLT transfers is as follows. All register
references are to SCV64 registers. For register details, please refer to Table 5.2 above.
1. Clear the DCSR register.
2. Set up the addressing and data transfer modes by writing to the MODE register. The
default to be used for setting this register should be 0x9480e401. The following bits
of the register may need to be changed - please refer to the descriptions in Table
5.2:
MODE<23>
MODE<20>
MODE<19>
MODE<18>
MODE<17>
MODE<16>
MODE<15:13>
MODE<12>
MODE<9>
3. Clear the DMALAR (local bus address) register.
4. Write the VMEbus address (least significant 32 bits for A64 address) to DMAVAR.
This is the destination address for a write operation from the ADC.
5. For A64 address cycles only, write the most significant 32 bits of the VMEbus
(source or destination) address to MA64BAR, using the following procedure:
i) Set MODE<12> to '1' (coupled mode).
ii) Write most significant 32 bits of VMEbus address to MA64BAR.
iii) Clear MODE<12>.
6. Write the transfer count (number of 32 bit longwords) to DMATC.
Содержание ICS-130
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