Transit Note #91
NOACT-ORBIT Data Sheet

Andre DeHon

Original Issue: August 1993

Last Updated: Fri Nov 5 13:24:27 EST 1993

Description and Features

NOACT-ORBIT is an implementation of METRO LINK (tn75) specialized to serve as a net-out. NOACT-ORBIT was fabricated in a gate-array technology by Orbit Semiconductor. NOACT-ORBIT serves to bridge an MBTA processing node and memory (tn38) into a METRO (tn73) network. Serving as a net-out, NOACT-ORBIT connects to a network input port and can originate messages from an MBTA node.

NOACT-ORBIT handles virtually all of the necessary low-level issues of message origination. It is intended to handle the portions of the network interface which must be implemented in hardware and are well understood now. NOACT-ORBIT handles:

converting messages between the double-word-wide MBTA node format and byte-wide METRO network format
selecting a ``random'' network port for outgoing transactions
generating and verifying end-to-end message checksums
generating control bytes ( e.g. TURN, DROP)
typical message retransmission
dummy cycle generation

METRO LINK Architectural Parameters

NOACT-ORBIT was compiled with the METRO LINK configuration bit NI set to zero. It supports an 8-bit wide data path. Additionally, to more robustly interface with networks constructed from cascaded, 4-bit METRO routing components, it has two separate forward and backward control bits allowing point-to-point port connections between NOACT-ORBIT and its attached METRO network. On the node side, NOACT-ORBIT supports a four-slot, 64-bit pipelined bus clocked at one-half the network speed. Processor NOACT-ORBIT communications are support during designated processor cycles using the low 32-bits of the 64-bit node datapath.

Artifacts

The second scan path ( TCK<1>, TMS<1>, TDI<1>, TDO<1>, TRST_L<1>) is a placeholder for future revisions which may support two scan paths. TDI<1> is connected directly to TDO<1> and the other signals are unused.

Pinout and I/O

NOACT-ORBIT requires 151 signal pins. Packaged in a 208-pin PQFP package, NOACT-ORBIT 57 power and ground pins (29 ground, 28 VCC). Figure shows the assignment of signal pins to package pins.

The pins function as follows:

For purposes of debugging, the state bits from the three main finite-state machines inside NOACT-ORBIT are available on output pins. Section details the symbolic-state encodings used by NOACT-ORBIT for these finite-state machines.

The enable signals associated with the bidirectional network lines are available as outputs. Since these enable signals are available outside the component, an unintelligent level-translator can serve to connect NOACT-ORBIT up to network components which do not use CMOS level signalling.

Clocking

NOACT uses NCLK to time synchronous communications with the network and NODE_CLK to time synchronous communications with the node. NODE_CLK should run at half the frequency of NCLK. (tn36) describes how METRO LINK bridges the gap between these two clocks and details the requisite NCLK- NODE_CLK phase relationship. NODE_CLK_OUT is a div-2 clock signal generated from NCLK and is suitably timed to serve as NODE_CLK or as a reference clock source for the generation of NODE_CLK. If buffering introduces sufficiently small delay (See (tn36)) and skew, NODE_CLK_OUT can be buffered to generate NODE_CLK. In high-performance systems, it will probably be necessary to use a PLL clock buffer/generator and use NODE_CLK_OUT from one of the METRO LINK components on the node as the reference clock.

Scan Path Description

NOACT-ORBIT has a single, functional TAP for configuration. It supports one non-bypass registers on the data scan path, and hence one non-bypass instruction. Table summarizes all the scan registers. The scan configuration register must be loaded with meaningful values in order for the component to perform properly. Configuration registers will retain their values across chip reset, but will not retain their values when the chip is powered down.

Instruction Register

When an instruction-shift is initiated through NOACT-ORBIT, the router will place the value 0b10101001 onto the scan path to comply with the IEEE TAP specification and to serve as an ad hoc component identification.

Configuration

Figure shows how the various METRO LINK configuration values are arranged in NOACT-ORBIT's configuration register. The values labelled ``unused'' exist in the configuration register for uniformity with NIACT-ORBIT (tn92), but their values have no effect on NOACT-ORBIT. The significance and interaction of these configuration options is detailed in (tn75).

Addresses and Encodings

Addresses

For NOACT-ORBIT A<12>=0 for all read/write operations. None of the address bits above bit 12 affect read or write operations to NOACT-ORBIT.

All the METRO LINK network interfaces on a node share the same address bus and nodenetwork control signals. The components use bits 11:8 of the address bus to determine which component should respond to each network read or write operation. Table summarizes the encodings.

Bits 7:4 select the register addressed by each read or write operation to which a given NOACT-ORBIT responds. Table summarizes the registers and their encodings. (tn81) and (tn75) explain how these registers are used by each METRO LINK component.

Operation Register

Writes to OPERATION and OPERATION_STG initiate or abort network operation. Table shows how the values written to these locations are used for message launch. Note that all fields listed in Table are updated by writes to OPERATION_STG. The values which are loaded only by OPERATION_STG writes will retain their current value when an OPERATION write is performed. (tn81) and (tn75) detail the role that these fields play in controlling message origination.

State Register

The STATE register contains data which indicates the status of NOACT-ORBIT including the current disposition of the most recently requested message launch. Table shows the fielding of data in this register. Table shows how to interpret the processor error field.

Configuration Register

The processor accessible configuration register contains three control bits which may need to be modified frequently in some situations. Table shows the placement of these configuration bits in the configuration register. When set, bit 7 tells NOACT-ORBIT to clear its error interrupt signal. The signal is cleared the whole time this bit is set, so it should be reset to zero after being cleared if the processor wishes to receive notification of any further errors. The offload configuration controls the amount of status information which NOACT-ORBIT offloads during message transmission. Table summarizes the encoding of this field.

Operation Encodings

Table summarizes the encodings for the primitive operations supported by NOACT-ORBIT. All other operation encodings may be used as user-defined, remote function invocations. (tn81) and (tn75) detail the behavior of these operations. These operation encodings are used when writing to the OPERATION and OPERATION_STG register addresses (See Table ) and can be seen in the STATE register (See Table ) after an operation has been launched.

Status Data

Table summarizes the information stored in each status double word. When configured to offload checksums, every other double word stored to the status-pointer address contains the router checksums collected along with the preceding status double word. Table summarizes the possible problem indications which may be stored in the status word problem indications.

Route Signalling Encodings

NOACT-ORBIT uses the encodings in Table to communicate with a METRO network. In dual router mode, NOACT-ORBIT provides separate control bits for each nibble of the 8-bit-wide data word. The data in each ROUTE word is taken directly from the ROUTE_WORD register, one byte at a time. Bit <10> (<11:10>) is the backward control bit used for fast-path reclamation. When this line is asserted (high), the downstream router (or NIACT-ORBIT) is blocked and is requesting that the connection be collapsed.

Message Checksums

Each data transmission through the network is guarded by a 16-bit CRC checksum. This checksum is initialized with the node number for the destination node and updated with each byte of the message between the beginning of the message and the first byte of the checksum. CHECK1 contains the bottom byte of the checksum and CHECK2 the top byte. The CRC checksum is computed using the CCITT 16-bit checksum polynomial [Int86] shown in Equation .

Checksum generation and verification is fully compatible with NIACT-ORBIT.

FSM Encodings

For potential debugging and statistics gathering purposes, NOACT-ORBIT makes the state bits for its three major finite-state machines available on package pins. The encodings for these states are summarized in Tables , , and . Refer to the source design data for the meaning of these states.

Configuration Requirement

NOACT-ORBIT is configured for operation in three parts:

static behaviour -- Configured via Scan Path (Section )
interrupt reset and output port selection -- Configured using CONFIGURATION (Section )
operation behaviour -- Configured using OPERATION_STG (Section )

All of these configuration options must be set for proper operation of the component. If the values set by OPERATION_STG do not change from operation to operation, subsequent operations can use the OPERATION address as a more terse way of launching messages.

Size

NOACT-ORBIT comprised approximately 25,000 gate-array gates and was fabricated on Orbit's base-array with 30K gates.

Timing

To Be Determined --

Related Components

NOACT-ORBIT and NIACT-ORBIT (tn92) have been designed to work with METROJR-ORBIT (tn90) to link processing nodes up to METRO style networks. Both NIACT-ORBIT and NOACT-ORBIT have an 8-bit network datapath. Using METROJR-ORBIT's width-cascading feature, a suitable network may be composed from pairs of METROJR-ORBIT routing components. In the dual-routers mode, the ports from NIACT-ORBIT and NOACT-ORBIT are designed to attach directly to such a cascaded network.

Bugs

Sept. 9, 1993 -- It looks like it is possible for processor wait to become asserted while NOACT-ORBIT is still offloading read data when in a mode that does not offload status and the number of dummy cycles is non-zero. As of this writing, I have not fully verified that this is a problem, but it looks possible that there may be a few cycles between the assertion of processor wait and the completion of the data write. We could put a deterministic upper bound on the number of cycles skewed if this really is the case. -- andre

Files

References

DeH91a: Andre DeHon. MBTA: Network Interface Implementation Notes. Transit Note 36, MIT Artificial Intelligence Laboratory, January 1991. [tn36 HTML link] [tn36 FTP link].
DeH91b: Andre DeHon. MBTA: Quick Overview. Transit Note 38, MIT Artificial Intelligence Laboratory, January 1991. [tn38 HTML link] [tn38 FTP link].
DeH92: Andre DeHon. METRO LINK -- METRO Network Interface. Transit Note 75, MIT Artificial Intelligence Laboratory, September 1992. [tn75 HTML link] [tn75 FTP link].
DeH93a: Andre DeHon. METROJR-ORBIT Datasheet. Transit Note 90, MIT Artificial Intelligence Laboratory, August 1993. [tn90 HTML link] [tn90 FTP link].
DeH93b: Andre DeHon. METRO LINK Programmer's Quick Reference. Transit Note 81, MIT Artificial Intelligence Laboratory, March 1993. [tn81 HTML link] [tn81 FTP link].
DeH93c: Andre DeHon. NIACT-ORBIT Datasheet. Transit Note 92, MIT Artificial Intelligence Laboratory, August 1993. [tn92 HTML link] [tn92 FTP link].
EDP +92: Eran Egozy, Andre DeHon, Samuel Peretz, Henry Minsky, and Thomas F. Knight Jr. METRO Architecture. Transit Note 73, MIT Artificial Intelligence Laboratory, August 1992. [tn73 HTML link] [tn73 FTP link].
Int86: International Telecommmunications Union, Geneva. The CCITT Red Book, 1986. Volume VIII, Recommendation V.41.

MIT Transit Project

Transit Note #91 NOACT-ORBIT Data Sheet