Atmel SpW-10X user manual SpaceWire Router, User Manual, Preliminary

SpW-10X	Ref.:	UoD_SpW-10X_
SpaceWire Router		UserManual
	Issue:	3.4
User Manual
	Date:	11th July 2008

In Figure 7-9 the format of the reply to a Read-Modify-Write command is illustrated. The first byte received by the SpaceWire router configuration logic is the port address followed by the destination logical address. Fields which are depicted in bold text are expected values. Fields which are shaded are optional. Note that the reply is always sent out of the same port as the command was received on. The Source Path Address should not include the output port of the router being commanded as the reply will be automatically sent out of the same port that the command arrived on. See section 7.6.8.

			First byte transmitted
			Source Path Address		Source Path Address			Source Path Address
Source Logical Address			Protocol Identifier		Packet Type, Command,			Status
			01h		Source Path Addr Len
Destination Logical Address			Transaction Identifier (MS)		Transaction Identifier (LS)			Reserved
	FEh							00h
Data Length (MS)			Data Length		Data Length (LS)			Header CRC
	00h		00h			04h
	Data (MSB)		Data			Data		Data (LSB)
	Data CRC		EOP
Last byte transmitted
Bits in Packet Type / Command / Source Path Address Length Byte
MSB										LSB
0		0	0	1	1		1	Source Path	Source Path
								Address Length	Address Length
	Packet Type			Command				Source Path Address Length

Figure 7-9 Read-Modify-Write Reply Packet Format

Table 7-13 Read-Modify-Write Reply Packet Fields

Field	Description	Bytes
Source Path	Optional source path addresses specified in the command packet. If no	0-12
Address	source path addresses are specified then the first byte will be the source
	logical address.
Source Logical	The source logical address specified in the command packet. If source	1
Address	path addresses are not used then the source logical address is the
	address of the return packet.
Protocol Identifier	The RMAP protocol identifier value 01h.	1
Command Byte	Read-Modify-Write reply command byte. The packet type bits in the	1
	command byte indicate this packet is a response packet.
Status	The command status is returned in this field. The command status can be	1
	command successful or an RMAP error code as defined in section 7.6.6.
Destination	The destination logical address is set to the default value FEh as the	1
	Preliminary	69