Module exchanger 

The Exchange Element governs data exchange between memory (via the M register) and other parts of the central compute unit (including the arithmetic element) via the E register.

The way in which the exchange element behaves is governed by the “System Configuration” which is a 9-bit value loaded from the F-memory. Which specific value is loaded from the F-memory is determined by the 5-bit configuration field within the current instruction; the instruction is loaded into the N register).

The standard set-up of the F-memory is described in Table 7-2 of the User Guide.

Structs

QuarterActivity 🔒

SystemConfiguration 🔒

The SystemConfiguration value specifies a global state of the computer which determines how the Arithmetic Element (in modern wording, arithmetic unit) communicates with memory. The basic outline is given in Fig. 9 (page 20) of “A Functional Description of the Lincoln TX-2 Computer” by John M. Frankovitch and H. Philip Peterson. A more complete description (including the corresponding F-memory values) is given in tables 7-2 and 7-2A of the TX-2 User’s Handbook (pp 192-193 in my PDF copy).

Enums

ExchangeDirection 🔒

The Exchange Element behaves differently in the M->E (i.e. load) direction and the E->M (i.e. store) direction. This enumeration specifies the direction of the current transfer.

Permutation 🔒

SubwordForm 🔒

Functions

apply_sign 🔒

exchanged_value_for_load 🔒

Perform an exchange operation suitable for a load operation; that is, emulate the operation of the exchange unit during e.g. LDA.

exchanged_value_for_load_without_sign_extension 🔒

Perform an exchange operation in the M->E direction, but without sign extension of the inactive quarters of the target.

exchanged_value_for_store 🔒

Perform an exchange operation suitable for a store operation; that is, emulate the operation of the exchange unit diring e.g. STE.

fetch_quarter 🔒

Determine which quarter of source gets permuted into target_quarter (numbered from zero), without regard to activity. Return the value of that quarter, shifted down into the lowest quarter (Q1, aka. quarter 0 when using u8 to indicate quarters).

permutation_source 🔒

Compute the quarter number (starting at 0) of the source word from which the values for target_quarter (also starting at 0) would be taken if it were active.

permute 🔒

Copy bits from source to dest, permuting them according to permutation. Only active quarters are modified.

quarter_mask 🔒

sign_extend 🔒

Perform sign extension. From User Handbook, figure 13-14, “The sign bit of an active quarter of a partially-active subword is extended to the left until an active quarter is again met, this must be interpreted in terms of the possible partially active subwords”. I don’t know what the second part of this sentence means. The accompanying diagram shows the sign bit being extended into quarters that are to the right of an active quarter (in order words the leftward extension wraps after it hits q4).

sign_extend_quarters 🔒

standard_plugboard_f_memory_settings 🔒