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Scratchpad Mode

Scratchpad mode is very similar to normal mode. In terms of the special instructons to be described in later sections, because it is almost identical in overall structure to normal mode, it is also identical in terms of which special instructions are available in that mode.

The format of the basic memory-reference instructions in this mode is:

The opcode space used in Normal Mode for memory-reference instructions performing arithmetic operations involving a memory location and one of the eight general registers or floating-point registers is now used for instructions that perform a load or store operation from the sixty-four supplementary registers of the appropriate type.

Also, a set of three-address register-to-register instructions is provided that are 32 bits in length, and which allow access to the base registers and the various types of scratchpad registers as well as the arithmetic-index registers, the floating-point registers, and the supplementary registers.

Thus, although there are instructions of different lengths, and many of the longer instructions still do not follow the load/store model, in this mode the processor has a full load/store instruction set similar to that of a RISC design, in addition to other non-RISC instructions.

These instructions have eight bits allocated to the opcode, divided between the first two halfwords of the instruction, but the first two bits of the opcode cannot both be 1. This allows these instructions to include additional opcodes for the instructions for the simple floating type, which will be discussed later.

In addition, since the fixed-point instructions of this group normally have the 64-bit supplementary registers as their destinations, a set of 32-bit integer instructions which use the high 32 bits of their destination register is provided. This is inspired by a similar feature recently added by IBM to its z/Architecture systems with the zEnterprise z196. It differs in that instructions working with the 8-bit or 16-bit types are not included, on the one hand, and, on the other, that multiplication and division instructions are added (but not the multiply extensibly and divide extensibly, which are more closely analogous to the multiply and divide instructions on the IBM 360 architecture).

One change to overall structure, which does not affect the availability of the various forms of additional instructions, is that the 16-bit instructions for moving data between the supplementary registers and the general registers, which begin with 010, were removed, and were replaced by the same compact set of memory-reference instructions for the general registers as used in local mode, although with their opcodes altered. This was felt to be reasonable, despite the fact that this mode emphasizes the scratchpad registers over the general registers, because without this change, the general registers would have been so isolated that the group of instructons removed would have had limited relevance in any case.

This compact set of memory-reference instructions is based on that used in compact mode, but with one important change. Since the full set of conditional jump, subroutine jump, and loop instructions is present elsewhere in this mode, it wasn't necessary to reserve space for a reduced subset of those instructions adjacent to the compact memory reference instructions in this mode.

Thus, an additional form of indexed instruction is provided with these characteristics:

The seven-bit opcodes are the same as those of the register-to-register instructions, but with the two most significant bits in the second halfword of the instruction.

The scratchpad registers are used as base registers for these instructions instead of the normal base registers.

These instructions use indirect addressing with post-indexing.

The eleven-bit address field in the instruction is shifted left two or three bits before use, depending on whether 32-bit or 64-bit addressing is in effect.

Thus, on the one hand, the compact memory-reference instructions allow the seven base registers from base register 1 through 7 to each point to an area of up to 65,536 bytes, which can contain simple variables.

On the other hand, instead of trying to fit all the arrays used by a program into these areas, which might mean that a whole base register is used up in order to allow a single huge array to be referenced, each of the seven scratchpad registers from scratchpad register 1 through 7 now points to a list of up to 2,048 addresses of arrays.

Thus, just as programs are free to use a large number of simple variables, they are also free to use a large number of arrays, restricted primarily by the amount of memory available, without the need to reload the base registers.

The cost of this feature, of course, is the extra memory access required due to resorting to indirect addressing. Because of this cost, the simple alternative of an indexed instruction where the index register is specified but the destination register must be register zero is also provided.

The opcodes of the memory-reference and register-to-register instructions in this format are:

Indexed           Register   Three-Address
-------------     ------     ------
0406xx 0x0xxx     0000xx     060xxx 00xxxx     SWB    Swap Byte
0416xx 0x0xxx     0001xx     060xxx 01xxxx     CB     Compare Byte
0426xx 0x0xxx     0002xx     060xxx 02xxxx     LB     Load Byte
0436xx 0x0xxx                                  STB    Store Byte
0446xx 0x0xxx     0004xx     060xxx 04xxxx     AB     Add Byte
0456xx 0x0xxx     0005xx     060xxx 05xxxx     SB     Subtract Byte

0506xx 0x0xxx     0010xx     060xxx 10xxxx     IB     Insert Byte
0516xx 0x0xxx     0011xx     060xxx 11xxxx     UCB    Unsigned Compare Byte
0526xx 0x0xxx     0012xx     060xxx 12xxxx     ULB    Unsigned Load Byte
0536xx 0x0xxx     0013xx     060xxx 13xxxx     XB     XOR Byte
0546xx 0x0xxx     0014xx     060xxx 14xxxx     NB     AND Byte
0556xx 0x0xxx     0015xx     060xxx 15xxxx     OB     OR Byte

0576xx 0x0xxx     0017xx     060xxx 17xxxx     STGB   Store if Greater Byte

0407xx 0x0xxx     0020xx     061xxx 00xxxx     SWH    Swap Halfword
0417xx 0x0xxx     0021xx     061xxx 01xxxx     CH     Compare Halfword
0427xx 0x0xxx     0022xx     061xxx 02xxxx     LH     Load Halfword
0437xx 0x0xxx                                  STH    Store Halfword
0447xx 0x0xxx     0024xx     061xxx 04xxxx     AH     Add Halfword
0457xx 0x0xxx     0025xx     061xxx 05xxxx     SH     Subtract Halfword
0467xx 0x0xxx     0026xx     061xxx 06xxxx     MH     Multiply Halfword
0477xx 0x0xxx     0027xx     061xxx 07xxxx     DH     Divide Halfword

0507xx 0x0xxx     0030xx     061xxx 10xxxx     IH     Insert Halfword
0517xx 0x0xxx     0031xx     061xxx 11xxxx     UCH    Unsigned Compare Halfword
0527xx 0x0xxx     0032xx     061xxx 12xxxx     ULH    Unsigned Load Halfword
0537xx 0x0xxx     0033xx     061xxx 13xxxx     XH     XOR Halfword
0547xx 0x0xxx     0034xx     061xxx 14xxxx     NH     AND Halfword
0557xx 0x0xxx     0035xx     061xxx 15xxxx     OH     OR Halfword
0567xx 0x0xxx     0036xx     061xxx 16xxxx     MEH    Multiply Extensibly Halfword
0577xx 0x0xxx     0037xx     061xxx 17xxxx     DEH    Divide Extensibly Halfword

0406xx 0x1xxx     0040xx     062xxx 00xxxx     SW     Swap
0416xx 0x1xxx     0041xx     062xxx 01xxxx     C      Compare
0426xx 0x1xxx     0042xx     062xxx 02xxxx     L      Load
0436xx 0x1xxx                                  ST     Store
0446xx 0x1xxx     0044xx     062xxx 04xxxx     A      Add
0456xx 0x1xxx     0045xx     062xxx 05xxxx     S      Subtract
0466xx 0x1xxx     0046xx     062xxx 06xxxx     M      Multiply
0476xx 0x1xxx     0047xx     062xxx 07xxxx     D      Divide

0517xx 0x1xxx     0051xx     062xxx 11xxxx     UC     Unsigned Compare

0537xx 0x1xxx     0053xx     062xxx 13xxxx     X      XOR
0547xx 0x1xxx     0054xx     062xxx 14xxxx     N      AND
0557xx 0x1xxx     0055xx     062xxx 15xxxx     O      OR
0567xx 0x1xxx     0056xx     062xxx 16xxxx     ME     Multiply Extensibly
0577xx 0x1xxx     0057xx     062xxx 17xxxx     DE     Divide Extensibly

0406xx 0x1xxx     0060xx     063xxx 00xxxx     SWL    Swap Long
0416xx 0x1xxx     0061xx     063xxx 01xxxx     CL     Compare Long
0426xx 0x1xxx     0062xx     063xxx 02xxxx     LL     Load Long
0436xx 0x1xxx                                  STL    Store Long
0446xx 0x1xxx     0064xx     063xxx 04xxxx     AL     Add Long
0456xx 0x1xxx     0065xx     063xxx 05xxxx     SL     Subtract Long
0466xx 0x1xxx     0066xx     063xxx 06xxxx     ML     Multiply Long
0476xx 0x1xxx     0067xx     063xxx 07xxxx     DL     Divide Long

0517xx 0x1xxx     0071xx     063xxx 11xxxx     UCL    Unsigned Compare Long

0537xx 0x1xxx     0073xx     063xxx 13xxxx     XL     XOR Long
0547xx 0x1xxx     0074xx     063xxx 14xxxx     NL     AND Long
0557xx 0x1xxx     0075xx     063xxx 15xxxx     OL     OR Long
0567xx 0x1xxx     0076xx     063xxx 16xxxx     MEL    Multiply Extensibly Long
0577xx 0x1xxx     0077xx     063xxx 17xxxx     DEL    Divide Extensibly Long

0406xx 1x0xxx     0100xx     064xxx 00xxxx     SWM    Swap Medium
0416xx 1x0xxx     0101xx     064xxx 01xxxx     CM     Compare Medium
0426xx 1x0xxx     0102xx     064xxx 02xxxx     LM     Load Medium
0436xx 1x0xxx                                  STM    Store Medium
0446xx 1x0xxx     0104xx     064xxx 04xxxx     AM     Add Medium
0456xx 1x0xxx     0105xx     064xxx 05xxxx     SM     Subtract Medium
0466xx 1x0xxx     0106xx     064xxx 06xxxx     MM     Multiply Medium
0476xx 1x0xxx     0107xx     064xxx 07xxxx     DM     Divide Medium

0506xx 1x0xxx     0110xx     064xxx 10xxxx     MEUM   Multiply Extensibly Unnormalized Medium
0516xx 1x0xxx     0111xx     064xxx 11xxxx     DEUM   Divide Extensibly Unnormalized Medium
0526xx 1x0xxx     0112xx     064xxx 12xxxx     LUM    Load Unnormalized Medium
0536xx 1x0xxx     0113xx                       STUM   Store Unnormalized Medium
0546xx 1x0xxx     0114xx     064xxx 14xxxx     AUM    Add Unnormalized Medium
0556xx 1x0xxx     0115xx     064xxx 15xxxx     SUM    Subtract Unnormalized Medium
0566xx 1x0xxx     0116xx     064xxx 16xxxx     MUM    Multiply Unnormalized Medium
0576xx 1x0xxx     0117xx     064xxx 17xxxx     DUM    Divide Unnormalized Medium

0407xx 1x0xxx     0120xx     065xxx 00xxxx     SWF    Swap Floating
0417xx 1x0xxx     0121xx     065xxx 01xxxx     CF     Compare Floating
0427xx 1x0xxx     0122xx     065xxx 02xxxx     LF     Load Floating
0437xx 1x0xxx                                  STF    Store Floating
0447xx 1x0xxx     0124xx     065xxx 04xxxx     AF     Add Floating
0457xx 1x0xxx     0125xx     065xxx 05xxxx     SF     Subtract Floating
0467xx 1x0xxx     0126xx     065xxx 06xxxx     MF     Multiply Floating
0477xx 1x0xxx     0127xx     065xxx 07xxxx     DF     Divide Floating

0507xx 1x0xxx     0130xx     065xxx 10xxxx     MEU    Multiply Extensibly Unnormalized
0517xx 1x0xxx     0131xx     065xxx 11xxxx     DEU    Divide Extensibly Unnormalized
0527xx 1x0xxx     0132xx     065xxx 12xxxx     LU     Load Unnormalized
0537xx 1x0xxx     0133xx                       STU    Store Unnormalized
0547xx 1x0xxx     0134xx     065xxx 14xxxx     AU     Add Unnormalized
0557xx 1x0xxx     0135xx     065xxx 15xxxx     SU     Subtract Unnormalized
0567xx 1x0xxx     0136xx     065xxx 16xxxx     MU     Multiply Unnormalized
0577xx 1x0xxx     0137xx     065xxx 17xxxx     DU     Divide Unnormalized

0406xx 1x1xxx     0140xx     066xxx 00xxxx     SWD    Swap Double
0416xx 1x1xxx     0141xx     066xxx 01xxxx     CD     Compare Double
0426xx 1x1xxx     0142xx     066xxx 02xxxx     LD     Load Double
0436xx 1x1xxx                                  STD    Store Double
0446xx 1x1xxx     0144xx     066xxx 04xxxx     AD     Add Double
0456xx 1x1xxx     0145xx     066xxx 05xxxx     SD     Subtract Double
0466xx 1x1xxx     0146xx     066xxx 06xxxx     MD     Multiply Double
0476xx 1x1xxx     0147xx     066xxx 07xxxx     DD     Divide Double

0506xx 1x1xxx     0150xx     066xxx 10xxxx     MEUD   Multiply Extensibly Unnormalized Double
0516xx 1x1xxx     0151xx     066xxx 11xxxx     DEUD   Divide Extensibly Unnormalized Double
0526xx 1x1xxx     0152xx     066xxx 12xxxx     LUD    Load Unnormalized Double
0536xx 1x1xxx     0153xx                       STUD   Store Unnormalized Double
0546xx 1x1xxx     0154xx     066xxx 14xxxx     AUD    Add Unnormalized Double
0556xx 1x1xxx     0155xx     066xxx 15xxxx     SUD    Subtract Unnormalized Double
0566xx 1x1xxx     0156xx     066xxx 16xxxx     MUD    Multiply Unnormalized Double
0576xx 1x1xxx     0157xx     066xxx 17xxxx     DUD    Divide Unnormalized Double

0407xx 1x1xxx     0160xx     067xxx 00xxxx     SWQ    Swap Quad
0417xx 1x1xxx     0161xx     067xxx 01xxxx     CQ     Compare Quad
0427xx 1x1xxx     0162xx     067xxx 02xxxx     LQ     Load Quad
0437xx 1x1xxx     0163xx                       STQ    Store Quad
0447xx 1x1xxx     0164xx     067xxx 04xxxx     AQ     Add Quad
0457xx 1x1xxx     0165xx     067xxx 05xxxx     SQ     Subtract Quad
0467xx 1x1xxx     0166xx     067xxx 06xxxx     MQ     Multiply Quad
0477xx 1x1xxx     0167xx     067xxx 07xxxx     DQ     Divide Quad

0507xx 1x1xxx     0170xx     067xxx 10xxxx     MEUQ   Multiply Extensibly Unnormalized Quad
0517xx 1x1xxx     0171xx     067xxx 11xxxx     DEUQ   Divide Extensibly Unnormalized Quad
0527xx 1x1xxx     0172xx     067xxx 12xxxx     LUQ    Load Unnormalized Quad
0537xx 1x1xxx     0173xx                       STUQ   Store Unnormalized Quad
0547xx 1x1xxx     0174xx     067xxx 14xxxx     AUQ    Add Unnormalized Quad
0557xx 1x1xxx     0175xx     067xxx 15xxxx     SUQ    Subtract Unnormalized Quad
0567xx 1x1xxx     0176xx     067xxx 16xxxx     MUQ    Multiply Unnormalized Quad
0577xx 1x1xxx     0177xx     067xxx 17xxxx     DUQ    Divide Unnormalized Quad

                             070xxx 00xxxx     SWHG   Swap High
                             070xxx 01xxxx     CHG    Compare High
                             070xxx 02xxxx     LHG    Load High
                             070xxx 03xxxx     STHG   Store High
                             070xxx 04xxxx     AHG    Add High
                             070xxx 05xxxx     SHG    Subtract High
                             070xxx 06xxxx     MHG    Multiply High
                             070xxx 07xxxx     DHG    Divide High

                             070xxx 11xxxx     UCHG   Unsigned Compare High

                             070xxx 13xxxx     XHG    XOR High
                             070xxx 14xxxx     NHG    AND High
                             070xxx 15xxxx     OHG    OR High

                             071xxx 00xxxx     SFSWL  Simple Floating Swap Halfword
                             071xxx 01xxxx     SFCL   Simple Floating Compare Halfword
                             071xxx 02xxxx     SFLL   Simple Floating Load Halfword

                             071xxx 04xxxx     SFAL   Simple Floating Add Halfword
                             071xxx 05xxxx     SFSL   Simple Floating Subtract Halfword
                             071xxx 06xxxx     SFML   Simple Floating Multiply Halfword
                             071xxx 07xxxx     SFDL   Simple Floating Divide Halfword

                             071xxx 10xxxx     SFMEUH Simple Floating Multiply Extensibly Unnormalized Halfword
                             071xxx 11xxxx     SFDEUH Simple Floating Divide Extensibly Unnormalized Halfword
                             071xxx 12xxxx     SFLUH  Simple Floating Load Unnormalized Halfword

                             071xxx 14xxxx     SFAUH  Simple Floating Add Unnormalized Halfword
                             071xxx 15xxxx     SFSUH  Simple Floating Subtract Unnormalized Halfword
                             071xxx 16xxxx     SFMUH  Simple Floating Multiply Unnormalized Halfword
                             071xxx 17xxxx     SFDUH  Simple Floating Divide Unnormalized Halfword

                             072xxx 00xxxx     SFSW   Simple Floating Swap
                             072xxx 01xxxx     SFC    Simple Floating Compare
                             072xxx 02xxxx     SFL    Simple Floating Load
                             072xxx 04xxxx     SFA    Simple Floating Add
                             072xxx 05xxxx     SFS    Simple Floating Subtract
                             072xxx 06xxxx     SFM    Simple Floating Multiply
                             072xxx 07xxxx     SFD    Simple Floating Divide

                             072xxx 00xxxx     SFMEU  Simple Floating Multiply Extensibly Unnormalized
                             072xxx 01xxxx     SFDEU  Simple Floating Divide Extensibly Unnormalized
                             072xxx 02xxxx     SFLU   Simple Floating Load Unnormalized

                             072xxx 04xxxx     SFAU   Simple Floating Add Unnormalized
                             072xxx 05xxxx     SFSU   Simple Floating Subtract Unnormalized
                             072xxx 06xxxx     SFMU   Simple Floating Multiply Unnormalized
                             072xxx 07xxxx     SFDU   Simple Floating Divide Unnormalized

                             073xxx 00xxxx     SFSWL  Simple Floating Swap Long
                             073xxx 01xxxx     SFCL   Simple Floating Compare Long
                             073xxx 02xxxx     SFLL   Simple Floating Load Long

                             073xxx 04xxxx     SFAL   Simple Floating Add Long
                             073xxx 05xxxx     SFSL   Simple Floating Subtract Long
                             073xxx 06xxxx     SFML   Simple Floating Multiply Long
                             073xxx 07xxxx     SFDL   Simple Floating Divide Long

                             073xxx 10xxxx     SFMEUL Simple Floating Multiply Extensibly Unnormalized Long
                             073xxx 11xxxx     SFDEUL Simple Floating Divide Extensibly Unnormalized Long
                             073xxx 12xxxx     SFLUL  Simple Floating Load Unnormalized Long
                             073xxx 14xxxx     SFAUL  Simple Floating Add Unnormalized Long
                             073xxx 15xxxx     SFSUL  Simple Floating Subtract Unnormalized Long
                             073xxx 16xxxx     SFMUL  Simple Floating Multiply Unnormalized Long
                             073xxx 17xxxx     SFDUL  Simple Floating Divide Unnormalized Long

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