Transit Note #90

METROJR-ORBIT Data Sheet

Andre DeHon

Original Issue: August 1993

Last Updated: Fri Nov 5 13:23:09 EST 1993

Description and Features

METROJR-ORBIT is a minimal implementation of the METRO router architecture (tn73) fabricated in a gate-array technology through Orbit Semiconductor. METROJR-ORBIT is a crossbar routing component suitable for constructing dilated, indirect, multistage networks. This component features:

METRO Architectural Parameters

METROJR has 4-bit wide, cascadable datapaths. It support 4 input and 4 output channels and can be configured either as a dilation one or dilation two routing component. Table summarizes the values of the METRO architecture variables which characterize METROJR-ORBIT. METROJR-ORBIT provides full support for port enable/disable and fast-path reclamation. METROJR-ORBIT support configuration using an IEEE 1149 compatible TAP [Com90] (See Section ), but does not support boundary scan.

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.

METROJR-ORBIT does not checksum the data streams it handles as would a full implementation of the METRO architecture. Instead, METROJR-ORBIT returns a pair of fixed patterns in place of the checksum. Since the basic fault-tolerance depends on the end-to-end checksums and not the router checksums, this omission does not prevent METROJR from serving as a fault-tolerant router (See details in (tn75)). The omission may make fault-localization more difficult than it would otherwise be.

Pinout and I/O

METROJR requires 67 signal pins. Packaged in an 84-pin PLCC package, we have 17 power and ground pins (9 ground, 8 VCC). Figure shows the assignment of signal pins to package pins.

The pins function as follows:

Scan Path Description

METROJR-ORBIT has a single, functional TAP for configuration. It supports three non-bypass registers on the data scan path, and hence three non-bypass instructions. Table summarizes all the scan registers. All three 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 METROJR-ORBIT, the router will place the value 0b11000101 onto the scan path to comply with the IEEE TAP specification and to serve as an ad hoc component identification.

Dilation

Table summarizes the encodings used in the dilation register. This register controls whether METROJR orbit behaves as a radix-4, dilation-1 (, ) router or as a radix-2, dilation-2 (, ) router.

Random Configuration

METROJR-ORBIT bases its random port selection in dilation-2 mode on two nominally-random input bits. For purposes of testing, METROJR-ORBIT can be configured to treat either or both inputs as a constant value. The four bits in the random register configure both random inputs separately as shown in Table . Table shows the encoding values used to configure each random input.

Port Configuration

Each forward port has seven bits of configuration in the port configuration register, and each backward port has six. Table shows the composition of this register. All single bit fields are positive and the corresponding behavior is enabled when the value is set to one. Variable turn delay specifies the number of clock cycles in the round-trip delay between between attached ports on distinct routers. Variable turn delay should be set to zero when the interconnect is treated as a single pipeline stage between routing components.

Encodings

Table shows the encodings which METROJR uses to implement the METRO routing protocol. When configured in dilation-1 mode specifies which of the four backward ports out which the message should be routed. When configured in the dilation-2 mode, is disregarded, and specifies whether to route the message out one of the high two backward ports or out one of the low two backward ports. The STATUS value indicates the actual backward port attained in undecoded form. If no backward port is allocated, the STATUS value will be zero; otherwise, the bit corresponding to the allocated backward port will be set and all others will be zero. Instead of returning a real checksum, METROJR-ORBIT returns a fixed pattern for CHECK0 and CHECK1. The sixth bit in each port is the backward drop line used for fast-path reclamation. When this line is asserted (high), the downstream router is blocked and is requesting that the connection be collapsed.

Size

METROJR-ORBIT comprised approximately 11,000 gate-array gates and was fabricated on Orbit's base-array with 15K gates.

Timing

To Be Determined --

Related Components

NIACT-ORBIT (tn92) and NOACT-ORBIT (tn91) have been designed to work with METROJR-ORBIT to link processing nodes up to a METRO style network. 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 their dual-routers mode, the ports from NIACT-ORBIT and NOACT-ORBIT are designed to attach directly to such a cascaded network.

See Also...

Files

References

Com90
IEEE Standards Committee. IEEE Standard Test Access Port and Boundary-Scan Architecture. IEEE, 345 East 47th Street, New York, NY 10017-2394, July 1990. IEEE Std 1149.1-1990.

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. NIACT-ORBIT Datasheet. Transit Note 92, MIT Artificial Intelligence Laboratory, August 1993. [tn92 HTML link] [tn92 FTP link].

DeH93b
Andre DeHon. NOACT-ORBIT Datasheet. Transit Note 91, MIT Artificial Intelligence Laboratory, August 1993. [tn91 HTML link] [tn91 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].

MIT Transit Project