User`s guide

DWMBB Adapter
3.2.5 DMA Write Transactions—Extended Address Modes
All DMA writes from the VAXBI are performed as disconnected writes.
Therefore, the VAXBI is released once the DMA command/address (C/A)
and write data to the DWMBB have been transferred, even though the
DWMBB has not completed the transaction on the XMI.
The execution of a DMA write transaction starts when the DWMBB/B
module detects a DMA write directed to memory space. The DWMBB/B
module sends the C/A and DMA write data to the DWMBB/A module over
the IBUS.
The DWMBB/A module latches the DMA C/A and write data off the IBUS.
The 30-bit VAXBI C/A is translated to the XMI 40-bit C/A using the
enabled translation mode. Then the DWMBB/A module arbitrates for the
XMI. When a grant is received, the DWMBB/A module issues the 40-bit
C/A to the XMI.
No status information is passed back to the originating VAXBI node, so
nodes do not know if the DMA write transaction completes successfully.
3.2.6 DMA Read Transactions—Extended Address Modes
All DMA reads from the VAXBI are performed as connected reads.
Therefore, possession of the VAXBI is maintained during the DMA read
transaction. The VAXBI cannot be used until the DMA read transaction is
completed or terminated.
The execution of a DMA read transaction starts when the DWMBB/B
module detects a DMA read directed to memory space. The DWMBB/B
module sends the C/A to the DWMBB/A module over the IBUS.
The DWMBB/A module latches the DMA C/A off the IBUS. The 30-
bit VAXBI C/A is translated to the XMI 40-bit C/A using the enabled
translation mode. Then the DWMBB/A module arbitrates for the XMI.
When a grant is received, the DWMBB/A module issues the DMA read on
the XMI.
Return DMA read data from the XMI is loaded into the DWMBB/A
module. The DWMBB/A module then signals the DWMBB/B module
that the DMA read data is available. Finally, the DWMBB/B module reads
the data from the DWMBB/A module and transfers it to the appropriate
VAXBI node.
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