12006 MAPLD International ConferenceSpaceWire 101 Seminar Differences Between RMAP & GAP Daniel Gilley Lockheed Martin 2006 MAPLD International Conference Washington, D.C. September 25, 2006

22006 MAPLD International ConferenceSpaceWire 101 Seminar Problems Associated with SpaceWire Network Implementations Standard SpaceWire packets provide: –No information about the nature of the data / desired operation –No way for the destination to reply with status to the source –No way to verify the data was transmitted correctly –No way to perform asynchronous read operations –… and more

32006 MAPLD International ConferenceSpaceWire 101 Seminar The Solution A protocol that lives inside a standard SpaceWire packet (‘upper layer protocol’) offers solutions to these problems, providing a basis for reliable transport within a network

42006 MAPLD International ConferenceSpaceWire 101 Seminar SpaceWire Packets

52006 MAPLD International ConferenceSpaceWire 101 Seminar Protocol ID Byte

62006 MAPLD International ConferenceSpaceWire 101 Seminar GAP Overview GAP (“General Access Protocol”) includes 3 transaction types –Write Request / Response –Read Request Untargeted / Response –Read Request Targeted / Response Each transaction includes a header with a command id, return address, options fields, a checksum, and command-specific information

72006 MAPLD International ConferenceSpaceWire 101 Seminar GAP Write / Response ‘A’ sends a write request to ‘B’ ‘A’ sends a write request to ‘C’ ‘B’ replies with a success response to ‘A’ ‘C’ replies with an error response to ‘A’

82006 MAPLD International ConferenceSpaceWire 101 Seminar GAP Targeted Read / Response ‘A’ sends a read request to ‘D’ ‘D’ replies with data for ‘A’ – the node in ‘A’ automatically puts the read data into memory and interrupts software when it is completed

92006 MAPLD International ConferenceSpaceWire 101 Seminar RMAP Overview RMAP, created by ESA, has 3 transactions: –Write Request / Response –Read Request / Response –Read-modify-write Request / Response Each transaction includes a header with packet type, source address, transaction ID, and transaction-specific information.

MAPLD International ConferenceSpaceWire 101 Seminar RMAP Write / Response ‘A’ sends an acknowledged write request to ‘B’ ‘A’ sends a verified write request to ‘D’ ‘B’ replies with a success response to ‘A’ ‘D’ replies with an error response to ‘A’

MAPLD International ConferenceSpaceWire 101 Seminar RMAP Read / Response ‘A’ sends a read request to ‘D’ ‘D’ replies with data for ‘A’ The software in ‘A’ reads the reply and takes appropriate action

MAPLD International ConferenceSpaceWire 101 Seminar RMAP Read-modify-write / Response ‘A’ writes masked data to a register in ‘C’ ‘C’ sends a success reply to ‘A’

MAPLD International ConferenceSpaceWire 101 Seminar GAP vs RMAP, Similarities GAP and RMAP are similar: –Both have read and write transactions –Both have the protocol ID byte –Both have similar fields in their headers –Both provide means for destinations to send replies to sources –Both provide an additional layer of data validation

MAPLD International ConferenceSpaceWire 101 Seminar GAP vs RMAP, Differences GAP provides: –Automatic copying of read reply data into the memory of the requesting device RMAP provides: –Verification of write data before it is written to destination memory –One transaction for read-modify-write operation

MAPLD International ConferenceSpaceWire 101 Seminar GAP vs RMAP Summary GAP is most useful in situations where there are a lot of packets that software has to process –Example: Flight software receiving regular telemetry data from various spacecraft subsystems RMAP is most useful in situations where small amounts of data need to be verified before being written –Example: A controller device with bitmapped values for control registers

MAPLD International ConferenceSpaceWire 101 Seminar Supporting GAP and RMAP Best solution would be a device which supports both GAP and RMAP Decoding method for each protocol could be determined by value of protocol byte or configuration register