PAPERS1 (June-August 1994)

Just as TTL_PAPERS was simplifying the PAPERS0 design, PAPERS1 was attempting to create a higher-performance enhanced version. Because it was to be the high-performance version, the PAPERS1 hardware has the dubious honor of having undergone enough revisions so that we lost count long ago. Phrases like "no, that PAL design is ancient... it's from last week" come to mind....

In any case, and, incidentally, the case of PAPERS1 is made of Pine, PAPERS1 does yield optimum performance. It is a full dynamic barrier mechanism with a variety of enhanced data communication operations, and all PAPERS1 operations require just 2 cycles. Inside the case....

Each PE corresponds to some TTL drivers and two AMD 22V10 PALS: one "barrier PAL" and one "communication PAL." This separation allowed PAPERS1 to perform both 1-bit multibroadcast (like PAPERS0) and a 4-bit multibroadcast that we now call "putget." (Currently, PAPERS1 has been upgraded by replacing 1-bit multibroadcast with NANDing as described below.) Making PAPERS1 capable of 2 cycle data transmission required a bit of cleverness implemented by a carefully crafted state machine. In essence, PAPERS1 internally simulates a multi-cycle data transmission using its own clock; this can yield near peak performance, but also makes it necessary to tune the internal clocking to the PC port and cable characteristics.

The board is wire-wrapped, but, unlike PAPERS0, wires were routed very carefully to minimize interference. Having 8 PALs meant a 300ma AC adapter wouldn't suffice, so there is a small switching power supply inside and an on/off switch on the back. The method for connecting cables and the LED display resemble those of the first TTL PAPERS.

It is also worthwhile to note that PAPERS1 upgraded the PAPERS0 concept of a parallel interrupt to include a special "interrupt acknowledge" barrier. Although the library still doesn't generally use this mechanism, it is used to achieve the initial synchronization when a parallel code begins execution. There is also a hardware ID feature that allows a PE to determine which PAPERS PE it is connected as -- earlier versions of PAPERS had to be explicitly given their PE number.

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