User`s guide

DWMBB Adapter
3.2.1.1 DWMBA Compatibility Mode DMA Write Transaction
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 is ACKed, 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 converted to the XMI C/A. Then the DWMBB/A
module arbitrates for the XMI. When a grant is received, the DWMBB/A
module issues the DMA write on the XMI.
No status information is passed back to the VAXBI node so the VAXBI
does not know if the DMA write transaction completes successfully.
3.2.1.2 DWMBA Compatibility Mode DMA Read Transaction
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 converted to the XMI C/A. 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.
3–9