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Distributed Interrupts for Real-Time Control in SpaceWire-Based On-Board Systems. Yuriy Sheynin, Sergey Gorbachev St. Petersburg State University of Aerospace Instrumentation Institute of High-Performance Computer and Network Technologies sheynin@aanet.ru.

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distributed interrupts for real time control in spacewire based on board systems

Distributed Interrupts for Real-Time Control in SpaceWire-Based On-Board Systems

Yuriy Sheynin, Sergey GorbachevSt. Petersburg State University of Aerospace Instrumentation

Institute of High-Performance Computer and Network Technologies

sheynin@aanet.ru

2006 MAPLD International Conference

Washington, D.C.

September 25, 2006

towards integral interconnection infrastructure for onboard systems
Towards integral interconnection infrastructure for onboard systems

Modern satellite and spacecraft distributed on-board systems have several (3-5) separate interconnections for different types of information and signals:

  • sensor busesfor data streams from sensors and instruments
  • command busesfor commands from controlunits to instruments and spacecraft equipment
  • telemetry bussesfor telemetry data
  • data busesfor data exchange between computing modules in the course of data and signal processing
  • time synchronization busesfor on-board clock synchronization
  • sideband signalsfor hard real-time signaling and control

Next generation modular spacecraft avionics should move towards integral interconnection infrastructure

SpaceWire is a candidate technology for such integral on-board interconnections

time codes distribution is a spacewire advantage
Time codes distribution is a SpaceWire advantage
  • The time codes distribution is a SpaceWire feature to substitute sideband signals for distributed systems clock synchronization. It is a clear advantage of the SpaceWire over other interconnection standards
  • Other signals, besides the time codes, are needed also to be distributed in SpaceWire-based interconnections
  • It is important to have them at the low protocol layer, in order to get high priority distribution, minimum latencies, to traverse blocked by data links, etc.It is ensured for time codes. Should be ensured for other signals also.
sideband signals into spacewire core interconnection
Sideband signals into SpaceWire core interconnection
  • Distributed on-board real-time systems need some signals (e.g., interrupts) distribution.
  • Sideband signal lines are used in previous generation on-board architectures
  • The trend in modern interconnections exclude sideband signals, include transfer of events, interrupts, etc. in the core interconnection itself, in its protocols;PCI Express is a good example
  • The SpaceWire also needs adequate means for substitution of sideband signals by its core interconnection means for signal distribution
the questions
The questions :
  • How many different signals?
  • What should be a mechanism for them?
  • How it correlates with the current and future SpaceWire standard releases?
  • To be aware: how it correlates with existing already SpaceWire implementations.
distributed interrupts mechanism in spacewire
Distributed Interrupts mechanism in SpaceWire

Proposal for next SpaceWire standard release:

  • Up to 64 different signals
  • Fits in the current SpaceWire character coding format
  • Leaves a space in the character coding format for further extension
  • Different, to the time-codes, mechanism for signal distribution:The reason: to have compact implementations for a mechanism that can support dozens of different signals running simultaneously in an interconnection
  • Do not violate fixed part of the SpaceWire standard,do not cause conflicts with existing SpaceWire standard compliant implementations
distributed interrupts and signals

0

1

1

0

1

0

0

1

T2

I2

E2

I2

T3

I3

I3

E3

I4

I4

E4

T4

E5

I5

I5

T5

P

P

P

P

P

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

P

1

0

0

Distributed Interrupts and Signals

“Time-codes”extensions –

Usage of Control Flags(bits T6 and T7 of Time codes)

a) ESC+L-char

NULL=ESC+FCT

b) ESC + N-Char

T6 T7

Time-code

1

0

T0

T1

Interrupt-code

I0

I1

1

0

Poll-code

1

0

I0

I1

Extension-code(reserved)

1

0

E0

E1

interrupt in master node

INTR_INsignal

Link controller

SpaceWire link

64-bit interrupt source register (ISR)

Poll_OUT signal

Interrupt in Master node

Poll code 15h

Interrupt 15h request

Host

Interrupt Code 15h

Interrupt 15h reset

0000…0…000

21st bit

1

interrupt code in target node

Poll_INsignal

Link controller

SpaceWire link

64-bit interrupt source register (ISR)

0000…0…000

INTR_OUT signal

21st bit

Interrupt code in Targetnode

Poll 15h request

Interrupt code 15 h

Host

Poll Code 15h

Interrupt 15h

1

interrupt code in a router node 0 in isr

INTR_IN signal

INTR_IN signal

Interrupt Code 15h

Link controller

j

Link controller

k

64-bit interrupt source register (ISR)

INTR_INsignal

SpaceWire link

SpaceWire link

SpaceWire link

Link controller

i

Interrupt Code 15h

0000…0…000

INTR_OUT signal

21st bit

Interrupt codein a Router node (‘0’ in ISR)

Interrupt code 15 h

Interrupt 15h

Interrupt 15h

1

interrupt code processing in a router node 1 in isr

INTR_IN signal

INTR_IN signal

Link controller

k

Link controller

j

64-bit interrupt source register (ISR)

INTR_INsignal

SpaceWire link

SpaceWire link

SpaceWire link

Link controller

i

0000…1…000

INTR_OUT signal

21st bit( 15h )

Interrupt codeprocessing in a Router node(‘1’ in ISR)

Interrupt code 15 h

poll code processing in a router node 1 in isr

Link controller

j

SpaceWirelink

Poll_IN signal

Poll Code 15h

64-bit interrupt source register (ISR)

Poll_INsignal

SpaceWirelink

Link controller

i

Link controller

k

SpaceWirelink

Poll_IN signal

Poll Code 15h

0000…0…000

Poll_OUT signal

21st bit

Poll codeprocessing in a Router node (‘1’ in ISR)

Poll code 15 h

Poll 15h

Poll 15h

1

poll code in a router node 0

Poll_IN signal

Poll_IN signal

Poll Code 15h

Link controller

j

Link controller

k

64-bit interrupt source register (ISR)

Poll_INsignal

SpaceWire link

SpaceWire link

SpaceWire link

Link controller

i

Poll Code 15h

0000…0…000

Poll_OUT signal

21st bit

Poll codein a Router node (‘0’)

Poll code 15 h

Poll 15h

Poll 15h

slide14

I=60h

I=60h

Router 2

Node 82

Master

Node 60

Slave

Interrupt-code: interrupt request. IRQ vector I=60h

Router 1

Router 3

Node 64

Slave

Node 74

Master

  • Poll-code: polling interrupt source status.
  • Packet: sending interrupt request source status.
slide15
Interrupt/Poll codes do not cause conflicts with existing SpaceWire standard compliant implementations

Interrupt/Poll codes are in conflict with Multi-Time codes

So,…

To have an interoperability

  • Modes of operation, set in the Configuration: either Interrupt/Poll codes, or Multi-Time codes.(also PCI <-> PCI-X compatibility is an example of the approach)
  • Not include in the SpaceWire standard neither Interrupt/Poll codes, nor Multi-Time codes.Treat them both as Logical (virtual) Sideband signals
    • NASA Multi-Time codes
    • RFSA Interrupt/Poll codes
  • Tunneling of “alternative” through the both type routers

To study carefully both Interrupt/Poll codes and Multi-Time codes specifications. Investigate particular level of their interoperability /non-interoperability.

interrupt poll codes in spacewire conclusion
Interrupt/Poll codes in SpaceWire. Conclusion
  • Former sideband signals, like interrupts, are integrated into SpaceWire interconnections
  • Up to 64 different signals can be distributed in an interconnection simultaneously
  • Interrupt/Poll codes are specified at the Symbol level. They have high priority for transmission and switching (next to Time codes)
  • Interrupt/Poll codes are distributed regardless of data transmission, cutting into data symbols flow at any link – idle, busy, blocked for data
  • Interrupt/Poll codes ensure low latency distribution. Latency boundaries can be estimated for a SpaceWire interconnection topology
  • Interrupt/Poll codes do not cause conflicts with existing SpaceWire standard and compliant with it implementations
  • Interrupt/Poll codes are implemented in our ASIC and FPGA SpaceWire implementation