Addressing; Accessing Remote I/O Node Csrs Through Mailboxes - DEC AlphaServer 8200 Technical Manual

When an I/O port receives a window write status return packet on the Up
Hose, it decrements its remote adapter node buffer counters and discards
the packet.
If the Memory Channel write address range does not fall within the range
of an associated valid outgoing Down Hose Range register, the I/O port dis-
cards the transaction and sets ICCNSE<3> (Memory Channel nonexistent
memory error). The I/O port then generates an interrupt on IPL 17, if the
ICCNSE<31> (interrupt enable) is set and ICCMSR<5> is clear.

6.4 Addressing

The I/O port supports the full address space of the TLSB, that is, one ter-
abyte of memory. This memory space is accessed through a 40-bit memory
address on the TLSB address bus.
The TLSB address bus is byte aligned. TLSB_ADR<39:5> on the TLSB ad-
dresses a specific hexword within the one terabyte of memory space. This
permits access to the 40-bit processor byte address.
The I/O port accesses all of memory as 64-byte blocks, using bits
TLSB_ADR<39:5> of the address bus as the memory address.
CSR registers on the I/O port module are aligned on 64-byte boundaries
and are accessed by other nodes through TLSB_ADR<27:6>.
The I/O port accesses the I/O Interrupt and I/O Window Control registers
in broadcast space through TLSB_ADR<27:6> of the address bus.
CSRs on remote I/O bus nodes are accessed by one of two methods:
If a nonexistent register within the I/O port's node space is read, the I/O
port ACKs the transaction and returns Unpredictable data to the request-
ing node.
If a nonexistent register within the I/O port's node space is written, the
I/O port ACKs the transaction and ignores the data. None of the I/O port's
internal registers are written.
The first two Mbytes of CSR locations of TLSB CSR space are reserved for
local use on each module. References to this region are serviced by re-
sources local to a module and therefore are never asserted on the TLSB.
The I/O port does not implement any CSRs in the reserved portions of CSR
space.
Broadcast space is used for write-only registers that are written in all
nodes. The I/O port uses this region to send interrupts to CPUs and to
control the flow of window space transactions.

6.4.1 Accessing Remote I/O Node CSRs Through Mailboxes

CSR requests are posted in a mailbox through software. The I/O port
reads the mailbox and passes it as a packet to the appropriate bus adapter.
When the bus adapter responds with a return status packet, the I/O port
returns the status and CSR read data to the mailbox in memory. Software
6-14 I/O Port
• TLSB mailbox protocol - to access nodes on the XMI I/O adapter and
the Futurebus+ adapter
• TLSB I/O window space - to access nodes on the PCI adapter