Motorola MVME172 - Manual (Page 131)

LCSR Programming Model
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Once the DMAC is enabled, the counter and control registers should not
be modified by software. When the command chaining mode is used, the
list of commands must be in local 32-bit memory and the entries must be
four-byte aligned.
A DMAC command list includes one or more DMAC command packets.
A DMAC command packet includes a control word that defines the
VMEbus AM code, the VMEbus transfer size, the VMEbus transfer
method, the DMA transfer direction, the VMEbus and local bus address
counter operation, and the local bus snoop operation. The format of the
control word is the same as the lower 16 bits of the control register. The
command packet also includes a local bus address, a VMEbus address, a
byte count, and a pointer to the next command packet in the list. The end
of a command is indicated by setting bit 0 or 1 of next command address.
The command packet format is shown in Table 2-2.
DMAC Registers
This section provides addresses and bit level descriptions of the DMAC
counters, control registers, and status registers. Other control functions are
also included in this section.
Table 2-2. DMAC Command Table Format
Entry Function
0 (bits 0-15) -- Control Word
1 (bits 0-31) Local Bus Address
2 (bits 0-31) VMEbus Address
3 (bits 0-31) Byte Count
4 (bits 0-31) Address of Next Command Packet