LCSR Programming Model

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.

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

 

 

 

 

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.

2

http://www.mcg.mot.com/literature

2-53

Page 131
Image 131
Motorola MVME172 manual Dmac Command Table Format, Dmac Registers, Entry Function