User guide

Figure 10–4 Outbound Scatter-Gather Entry
31 08 06 05 04 00
ML013328
Function Code <2:1>
Address Size <1:0>
o/b VME Page
RMW
Swap <2:0> Mode
Valid
PCI Addr <28:18>
0910111213141718
MBZ
X
31 02 01 00
o/b VME Page <31:18>
VME Addr <31:0>
1718
00
PCI Addr <17:2>
A PCI memory access in either VME WINDOW_1 or VME WINDOW_2 address
windows causes a lookup for the corresponding scatter-gather entry. That is,
if PCI Address bits <31:29> match the VME_WINDOW_1_BASE register or
if PCI Address bits <31:26> match the VME_WINDOW_2_BASE register, a
scatter-gather lookup occurs.
The scatter-gather entry is identified using either PCI address bits <28:18> or
PCI address bits <25:15>. If the PCI memory cycle addresses VME_WINDOW_1,
the scatter-gather entry is identified by PCI address bits <28:18>. If the PCI
memory cycle addresses VME_WINDOW_2, the scatter-gather entry is identified
by PCI address bits <25:18>.
Bits <31:18> of the scatter-gather entry provide the page address (VME address
bits <31:18>) of the corresponding VMEbus page. PCI address bits <17:2>,
together with the PCI byte enables, specify the byte address within that page.
Once the correct scatter-gather entry is identified, its valid bit, <5>, is checked.
If the valid bit is set, the VME interface forms the VMEbus address from the
scatter-gather entry. If the bit is not set, the scatter-gather entry is invalid
and no VMEbus transaction can occur. Instead, the outbound Error bit in the
VME Interface Processor Bus error/status register (VIP_BESR) is set. If the
corresponding bit is also set in the VME interface processor interrupt control
register (VIP_ICR), this event causes a DC7407 interrupt assertion.
The following sections describe the other fields of the scatter-gather entry.
VME Interface 10–5