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FPP

Class: FPP

In the 1960-1970s the so called FPP-12 floating point processor was announced in conjunction with the PDP-12 computer. In 1970 this processor was also made accessible to the following range of computers as detailed in 'FPP-12 Users Manual'. To quote: The Floating Point Processor (FPP-12) is a programmable, peripheral, digital processor that attaches to the input/output (I/0) bus of any PDP-8, PDP-8/1, PDP-8/L, PDP-8/E, LINC-8, or PDP-12 Computer. The FPP-12 is a parallel processor with its own instruction set. It was not very successful on non PDP-12 machines, due to its bulk (good part of a cabinet).

In 1975 the availability of better integrated circuits led to the PDP-8/A computer. This computer had a wider Omnibus, which allowed the creation of more compact modules. One of these modules was the FPP8A as described there 'FPP8-A Users Manual' :

The FPP8-A is a processor that performs arithmetic calculations with floating-point numbers. It is compatible with the FPP12-A instruction set and will run OS8 FORTRAN IV without program modi­fication; with minor program changes, the FPP8-A will run FORTRAN IV at higher speeds.

The FPP8-A consists of two interconnected, hex-size, printed-circuit modules that plug into the Omnibus of a PDP-8/A computer. There are no connections from the FPP to external devices, and the FPP derives all of its power from the Omnibus. When the PDP-8 is turned on, the FPP remains inactive until started by IOT instructions issued by the Central Processing Unit. Once started, the FPP retrieves instructions and operands from the PDP-8 memory by data breaks; many data manipulations and arithmetic calculations are then carried out independently of the CPU and at a higher speed than is possible with CPU timing. The FPP continues to run until halted by an IOT instruction or an FPP instruction, until it encounters numbers that are too large or too small to handle, or until the PDP-8 is halted.

But in the process of making our latest release of OS/8 (V50) and in the process of editing the FRTS source the interfacing to the FPP came up. I decided to implement the functions of the FPP8-A as described in 'FPP8-A Maintenance Manual'.
Excerpt from this User Guide:
Other publications that contain instructive information about the FPP and its relationship to the PDP-8 are:
a. FPP8-A Diagnostic, MAINDEC-08-DJFPA
b. FPP8-A Instruction Test and Data Exerciser, MAINDEC-08-DJFPB
c. PDP-8/E, 8/F, and 8/M Maintenance Manual
d. PDP-8/A Miniprocessor User's Manual. 1-3

The testing procedure as detailed in the aformentioned User Guide tells us that the appropriate testing programs is called MAINDEC-08-DJFPA and MAINDEC-08-DJFPB. The only binaries I have found are DJFPAB and DJFPBC. Because no listing exists I had to recompile these binaries.
The recompilatiuon was done using the information in the 'FPP8-A Field Maintenance Print Set' and 'FPP8-A Maintenance Manual'. The following list shows the test program. Under 'Test program' the name of the test program to be found under 'Tests', under 'Source' the respective sources that were used to produce the executables, under 'Testing procedure' the instructions for executing the test.

.RU RKAl DJFPAB 

 FPP-8A DIAGNOSTIC DJFPA-B
 RUN ALL TESTS?Y

 SETUP CONTROL SWITCHES = 0000

 RUNNING

 FPP MICRO CODE REV = 00

 FPP MPC ERROR     LOC: 4035    BAD MODULE IS M8410
 ACTUAL: 0000 EXPECTED: 0300 STATUS: 0015 TEST: 0004 STEP: 0000

 ^G SR=  0000

.RU RKAl DJFPBC 

 FPP-8A INST. TEST AND DATA EXERCISER 
 MAINDEC-08-DJFPB-C 

 SR=0000

 TYPE "I" FOR FPP-8A INST. TEST ONLY 
 TYPE "E" FOR FPP-8A EXERCI ER ONLY 
 TYPE "B" FOR BOTH FPP-8A INST. AND EXERCISER TESTS            

 *B

 FPP-8A DATA EX. RELOC? (Y OR N) : Y 
 FPP-8A DATA EX. QUICK VERIFY? (Y OR N) : Y 

 RUNNING FPP-8A INSTR. TEST 
 DJFPB: FPP-8A IMSTR. TEST PASS: 0001 

 RUNNING FPP-8A DATA EX. 
 DJFPB: FPP-8A DATA EX. PASS: 0001 

The programs can be found on the MyProgs disk (DJFPAB.SV and DJFPBC.SV).