GR712RC-UM, Jun 2017, Version 2.9 116 www.cobham.com/gaisler
GR712RC
enabled only on core GRSPW2-0 and on core GRSPW-1. This section describes the basics of the
RMAP protocol and the command handler implementation.
16.6.1 Fundamentals of the protocol
RMAP is a protocol which is designed to provide remote access via a SpaceWire network to memory
mapped resources on a SpaceWire node. It has been assigned protocol ID 0x01. It provides three oper-
ations write, read and read-modify-write. These operations are posted operations which means that a
source does not wait for an acknowledge or reply. It also implies that any number of operations can be
outstanding at any time and that no timeout mechanism is implemented in the protocol. Time-outs
must be implemented in the user application which sends the commands. Data payloads of up to 16
MiB - 1 is supported in the protocol. A destination can be requested to send replies and to verify data
before executing an operation. A complete description of the protocol is found in the RMAP standard.
16.6.2 Implementation
The GRSPW includes an handler for RMAP commands which processes all incoming packets with
protocol ID = 0x01, type field (bit 7 and 6 of the 3rd byte in the packet) equal to 01b and an address
falling in the range set by the default address and mask register. When such a packet is detected it is
not stored to the DMA channel, instead it is passed to the RMAP receiver.
The GRSPW implements all three commands defined in the standard with some restrictions. The
implementation is based on draft F of the RMAP standard (the only exception being that error code 12
is not implemented). Support is only provided for 32-bit big-endian systems. This means that the first
byte received is the msb in a word. The command handler will not receive RMAP packets using the
extended protocol ID which are always dumped to the DMA channel.
The RMAP receiver processes commands. If they are correct and accepted the operation is performed
on the AHB bus and a reply is formatted. If an acknowledge is requested the RMAP transmitter auto-
matically send the reply. RMAP transmissions have priority over DMA channel transmissions.
Packets with a mismatching destination logical address are never passed to the RMAP handler. There
is a user accessible destination key register which is compared to destination key field in incoming
packets. If there is a mismatch and a reply has been requested the error code in the reply is set to 3.
Replies are sent if and only if the ack field is set to ‘1’.
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