1. SpaceWire Remote Memory Access Protocol
Steve Parkes
Space Technology Centre
University of Dundee
Scotland, UK

2. Remote Memory Access Protocol Provide a means of
Aims of RMAP
Remote Memory Access Protocol
Provide a means of
Writing to
Reading from
Registers or memory on a SpaceWire node
Over a SpaceWire network
Registers are considered to be memory mapped
Simple and effective
Flexible
encompassing diverse applications

3. RMAP Commands Write Read Read-Modify-Write
With or without acknowledgement
Verifying data before writing or writing without verification
Read
Read-Modify-Write

4. Write Operation RMAP Source RMAP Destination Write Request Write
Command
Write Data
Request
USER
APPLICATION
USER
APPLICATION
Write Data
Authorisation
Write Data
Write
Reply
Write Data
Indication
Write Complete
Confirmation
SpaceWire
Network

5. Write Commands Write non-acknowledged, non-verified
Writes zero or more bytes to memory in a destination node
Command header is checked using a CRC before the data is written
Data is not checked before it is written
No acknowledgement given to indicate that the command has been successfully executed
Used for writing large amounts of data to a destination
Where it can be safely assumed that
The write operation completed successfully
Or that is not critical if it does not succeed
E.g. writing camera images to a temporary working buffer

6. Write Commands Write non-acknowledged, verified
Writes zero or more bytes to memory in a destination node
Command and data are both checked using CRCs before the data is written
Limits the amount of data that can be transferred in a single write operation
Owing to limited buffer space in destination
Erroneous data cannot be written to memory
No acknowledgement given to indicate that the command has been successfully executed
Used for writing command registers and small amounts of data to a destination
where it can be safely assumed that
the write operation completed successfully
or where errors are detected in a different way
E.g. writing many commands to different configuration registers in a device and then checking for an error using a status register

7. Write Commands Write acknowledged, non-verified
Writes zero or more bytes to memory in a destination node
Command is checked using a CRC before the data is written
Data is not checked before it is written
Acknowledgement sent to indicate that the command has been successfully executed
used for writing large amounts of data to a destination
where it can be safely assumed that
the write operation completed successfully,
but an acknowledgement is required.
For example writing sensor data to memory.

8. Write Command Write acknowledged, verified
Writes zero or more bytes to memory in a destination node
Command and data are both checked using CRCs before the data is written
Limits the amount of data that can be transferred in a single write operation
Owing to limited buffer space in destination
Erroneous data cannot be written to memory
Acknowledgement sent to indicate that the command has been successfully executed
Used for writing small amounts of data to a destination
where it is important to have confirmation that
the write operation was executed successfully.
For example writing to command or configuration registers.

9. Write Command – Logical Addressing
First byte transmitted
Destination Logical Address
Protocol Identifier
Packet Type, Command,
Source Path Addr Len
Destination Key
Source Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Extended Write Address
Write Address (MS)
Write Address
Write Address
Write Address (LS)
Data Length (MS)
Data Length
Data Length (LS)
Header CRC
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data CRC
EOP
Last byte transmitted
Bits in Packet Type / Command / Source Path Address Length Byte
MSB
LSB
Reserved
= 0
Command
= 1
Write = 1
Verify data(1)
No Verify (0)
Ack (1)/
No ack (0)
Increment/
No inc. addr
Source Path
Address Len = 0
Source Path
Address Len = 0
Packet Type
Command
Source Path Address Length

10. Definitions Destination Logical Address Protocol Identifier
SpaceWire logical address of destination
Protocol Identifier
01h for RMAP protocol
Packet Type/Command/Source Path Length
Packet type: 2-bit field
00 = reply
01 = command
10 = Reserved
11 = Reserved
Command: 4-bit field
Contains the RMAP command code
Source Path Address Length: 2-bit field
For logical addressing these two bits are always 00

11. Definitions Destination Key Source Logical Address
One byte key
Must be matched by the user application
For command to be authorised
Source Logical Address
SpaceWire logical address of the source of the RMAP command
Needed in a command so that the destination knows where to send reply
Transaction Identifier
Two byte identifier
Allows source to send out multiple commands
Each with distinct transaction identifier
Transaction identifier included in reply
Allows source to associate
Reply
With command that caused the reply

12. Definitions Extended Write Address Write Address Data Length
Extends 32-bit write address to 40-bits
May be used to differentiate memory spaces in a destination
E.g.
00h may indicate register addresses
01h may indicate memory bank one
Write Address
32-bit destination memory address
Where data is to be written
Note that registers etc are memory mapped
Data Length
Length of data to be written in bytes
Header CRC
CRC8
8 bit CRC covering the header
Starting with and including the destination logical address

13. Definitions Data Data CRC EOP
The data to be written into memory/registers
At the destination
Data CRC
CRC8
8-bit CRC
Covers all data
Not useful for long packets
EOP
SpaceWire End of Packet Marker

14. Write Reply – Logical Addressing
First byte transmitted
Source Logical Address
Protocol Identifier
Packet Type, Command,
Source Path Addr Len
Status
Destination Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Header CRC
EOP
Last byte transmitted
Bits in Packet Type / Command / Source Path Address Length Byte
MSB
LSB
Reserved
= 0
Response
= 0
Write = 1
Verify data (1)
No Verify (0)
Ack = 1
Increment/
No inc. addr
Source Path
Address Len = 0
Source Path
Address Len =0
Packet Type
Command
Source Path Address Length

15. Definitions Status Status of command
Set to zero if command executed correctly
Non-zero if there was an error

16. Write Command – Path Addressing
First byte transmitted
Destination Path Address
Destination Path Address
Destination Path Address
Destination Logical Address
Protocol Identifier
Packet Type, Command,
Source Path Addr Len
Destination Key
Source Path Address
Source Path Address
Source Path Address
Source Path Address
Source Logical Address
Transaction Identifier (LS)
Transaction Identifier (MS)
Extended Write Address
Write Address (MS)
Write Address
Write Address
Write Address (LS)
Data Length (MS)
Data Length
Data Length (LS)
Header CRC
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data CRC
EOP
Last byte transmitted
Bits in Packet Type / Command / Source Path Address Length Byte
MSB
LSB
Reserved
= 0
Command
= 1
Write = 1
Verify data(1)
No Verify (0)
Ack (1)/
No ack (0)
Increment/
No inc. addr
Source Path
Address Length
Source Path
Address Length
Packet Type
Command
Source Path Address Length

17. Definitions Destination Path Address Source Path Address
SpaceWire path address from source to destination
Source Path Address
SpaceWire path address from destination back to source
Multiple of 4 bytes
Leading zero bytes are ignored
Example
results in path address 01 03
Source Path Address Length Field
Number of 32-bit words needed to hold source path address
Five byte source address requires two 32-bit words
E.g
Source path address then set to 10b

18. Write Reply – Path Addressing
First byte transmitted
Source Path Address
Source Path Address
Source Path Address
Source Logical Address
Protocol Identifier
Packet Type, Command,
Source Path Addr Len
Status
Destination Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Header CRC
EOP
Last byte transmitted
Bits in Packet Type / Command / Source Path Address Length Byte
MSB
LSB
Reserved
= 0
Response
= 0
Write = 1
Verify data (1)
No Verify (0)
Ack = 1
Increment/
No inc. addr
Source Path
Address Length
Source Path
Address Length
Packet Type
Command
Source Path Address Length

19. Write Command Header Error
Source
Destination
Write Request
Write
Command
Record
Packet
Error

20. Write Authorisation Rejection
Source
Destination
Write Request
Write
Command
Write Data
Request
Write Data
Authorisation
Rejection
Write Reply
Error
Authorisation
Failure

21. Command Authorisation
Destination user application
Can refuse to authorise command for any reason
E.g.
Write address not 32-bit aligned
Length not a multiple of four bytes
Address range falls partially or completely outside an acceptable region

22. Write Data Error Source Destination Write Request Write Command Header
Authorisation
Record
Data Error
Write Data
Error Reply
Write Data
Error Indication
Write Data
Failure

23. Write Reply Error Source Destination Write Request Write Command
Write Data
Request
Write Data
Authorisation
Write Data
Write
Reply
Write Data
Indication
Record
Packet
Error

24. Read Command Read command Reads zero, one or more bytes of data
From specified area of memory in a destination node
Data read is returned in a reply packet.

25. Read Operation Source Destination Read Request Read Command Read Data
Response
Read
Reply
Read Data
Confirmation

26. Read Command – Logical Addressing
Read Address (MS)
Read Address
Read Address (LS)
Data Length (MS)
Data Length
Data Length (LS)
Header CRC
EOP
First byte transmitted
Last byte transmitted
Destination Logical Address
Protocol Identifier
Packet Type, Command
Source Path Addr Len
Destination Key
Source Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Extended Read Address
Read = 0
Command
= 1
Increment/
No inc. addr
Read = 1
(Ack/No_Ack)
Reserved
= 0
Bits in Packet Type / Command / Source Path Address Length Byte
MSB
Packet Type
Source Path
Address Len = 0
LSB
Source Path Address Length

27. Definitions Extended Read Address Read Address
Extends 32-bit read address to 40-bits
May be used to differentiate memory spaces in a destination
E.g.
00h may indicate register addresses
01h may indicate memory bank one
Read Address
32-bit destination memory address
From which data is to be read
Note that registers etc are memory mapped

28. Read Reply – Logical Addressing
Source Logical Address
Protocol Identifier
Packet Type, Command,
Source Path Addr Len
Status
Destination Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Reserved = 0
Data Length (MS)
Data Length
Data Length (LS)
Header CRC
Data
Data CRC
EOP
First byte transmitted
Last byte transmitted
Read = 0
Response
= 0
Increment/
No inc. addr
Read = 1
(Ack/No Ack)
Reserved
Bits in Packet Type / Command / Source Address Path Length Byte
MSB
Packet Type
Command
Source Path
Address Length
LSB
Source Path Address Length

29. Read-Modify-Write Command
Reads a register (or memory)
Returns its value
Writes a new value, specified in the command, to the register.
Mask can be included, in the command
So that only certain bits of the register are written
Provides an atomic operation that can be used for semaphores and other handshaking operations.

30. Read-Modify-Write Operation
Source
Destination
RMW Request
RMW
Command
RMW Data
Request
Data Read and Write
Authorisation
Write Data
RMW
Reply
Write Data
Indication
RMW Complete
Confirmation

31. Example Read-Modify-Write Operation1 1
Data in command (Data) 1 1 1 1
Mask in command (Mask) 1 1 1 1 1
Data read from destination memory and returned to source (Read) 1 1 1 1 1
Data written to destination memory
= (Mask AND Data) OR (NOT Mask.Read)

32. Read-Modify-Write Command – Logical
Verify Data
Before Wr = 1
Command
= 1
Incr. address
Ack/No_Ack
Reserved
= 0
Bits in Packet Type / Command / Source Address Path Length Byte
MSB
Packet Type
Destination Logical Address
Protocol Identifier
Packet Type, Command
Source Path Addr Len
Destination Key
Source Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Extended RMW Address
RMW Address (MS)
RMW Address
RMW Address (LS)
Data +Mask Length (MS)
= 00h
Data + Mask Length
Data + Mask Length (LS)
= 00h, 02h, 04h, 06h or 08h
Header CRC
Data (MS)
Data
Data (LS)
Data/Mask CRC
EOP
First byte transmitted
Last byte transmitted
Mask (MS)
Mask
Mask (LS)
Source Path
Address Len = 0
LSB
Source Path Address Length

33. Definitions Data + Mask Length Data
Length of data and mask information
00, 02, 04, 06, or 08h.
Data
Up to four bytes of data to be combined with
Data in addressed memory and
Mask
Then written into addressed memory
Value originally in addressed memory will be returned
Up to four bytes of information that determine
How data is to be used
To update addressed memory

34. Read-Modify-Write Reply – Logical
Source Logical Address
Protocol Identifier
Packet Type, Command,
Source Path Addr Len
Status
Destination Logical Address
Transaction Identifier (MS)
Transaction Identifier (LS)
Reserved = 0
Data Length (MS) = 0
Data Length = 0
Data Length (LS)
= 01h, 02h, 03h or 04h
Header CRC
Data
Data CRC
EOP
First byte transmitted
Last byte transmitted
Read = 0
Verify Data
Before Wr = 1
Response
= 0
Inc. address
= 1
Ack/No_Ack
Reserved
Bits in Packet Type / Command / Source Path Address Length Byte
MSB
Packet Type
Command
Source Path
Address Len = 0
LSB
Source Path Address Length

35. Partial Implementation of RMAP
Partial implementations are permitted
For example:
Support of write and read but not RMW commands
Support of 32-bit data lengths only
If destination receives command it does not support
Or command with options not supported
It refuses to authorise the command
Command is not executed
If reply requested then it will contain Authorisation Failure error code

36. Write to Memory with DMA
SpaceWire
Interface
RMAP
Interface
DMA Controller
Memory
SpaceWire
MemPtr = h
Data
DataCtr = h
Data
SpaceWire-RMAP Interface
Destination Application

37. Example RMAP command writing to memory
Field
No. Bytes
Value
Destination Path Address -
Destination Logical Address 1
54h
Protocol Identifier
01h
Packet Type
01b
Command
1011b
Extra Source Path Address Length
00b
Extra Source Path Address
Destination Key
42h
Source Logical Address
76h
Transaction Identifier 2
0004h
Extended Write Address
00h
Write Address 4 h
Data Length 3 h
Header CRC
8dh
Data 16
0001h 0203h 0405h 0607h
0809h 0a0bh 0c0dh 0e0fh
Data CRC
TOTAL 33

38. Write to Mailbox with DMA
SpaceWire
Interface
RMAP
Interface
Mailbox DMA
Mailbox Base Ptr
Mailbox Current Ptr
Mailbox Max Size
Mailbox Status
Mailbox Data Size
Memory
Mailbox Memory
SpaceWire-RMAP Interface
Destination Application

39. Example RMAP command writing to mailbox
Field
No. Bytes
Value
Destination Path Address -
Destination Logical Address 1
54h
Protocol Identifier
01h
Packet Type
01b
Command
1010b
Extra Source Path Address Length
00b
Extra Source Path Address
Destination Key
99h
Source Logical Address
76h
Transaction Identifier 2
0006h
Extended Write Address
Write Address 4 h
Data Length 3 h
Header CRC
a5h
Data 16
0001h 0203h 0405h 0607h
0809h 0a0bh 0c0dh 0e0fh
Data CRC
8dh
TOTAL 33

40. Summary RMAP provides:
A consistent means of reading and writing
Registers and memory
Over SpaceWire network
Is very flexible
Partial implementation permitted
Is being implemented in
ESA Router ASIC
ESA Remote Terminal Computer
JAXA devices
Draft E of standard has been extensively reviewed
Will become ECSS-E50-11
Currently being implemented in at least two ASICs