208 lines
8.8 KiB
Markdown
208 lines
8.8 KiB
Markdown
Thingamajig v2.0
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================
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Thingamajig v2.0 is a RISC/MISC homebrew computer architecture. Its git
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repository can be found at
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https://ahti.space/git/crazyettin/Thingamajig.
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Included Software
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-----------------
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The repository includes an emulator implementation of Thingamajig with
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device control programs, and an assembler and a disassembler, all
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written in FreePascal. It also includes couple of simple example
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programs for Thingamajig written in assembly.
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Registers and Memory
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--------------------
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* 24-bit instruction register IR
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* 16-bit instruction and return pointers IP and RP
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* 8-bit general-purpose registers R0-R3
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* 8-bit memory locations 0-FFFF
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Multi-byte values are big-endian. Memory locations 0-FFEF are used for
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RAM while FFF0-FFFF are reserved for memory mapped devices.
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Input and output are mapped to address FFFF, while arbitrary devices can
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be mapped to the other reserved addresses. When interacting with memory
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mapped devices Thingamajig will stop processing to wait for the device
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to be ready if needed.
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Instructions
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------------
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Instructions without an immediate or address argument are 8-bit, those
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with an immediate one 16-bit, and those with an address one 24-bit. The
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instruction pointer is incremented before being accessed or modified.
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0 HALT
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1 RET IP = *RP; RP += 2
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2 SHL RX, N RX <<= N (logical) Shifts of 1-4 steps,
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3 SHR RX, N RX >>= N (logical) with 4 encoded as 0
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4 ROL RX, N RX <<= N (rotating) in machine code.
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5 ROR RX, N RX >>= N (rotating)
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6 NAND RX, RY RX = ~(RX & RY)
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7 AND RX, RY RX &= RY
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8 OR RX, RY RX |= RY
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9 XOR RX, RY RX ^= RY
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A LOAD RX, ~0, IMM RX = IMM Written as "LOAD RX, #IMM"
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0, ADDR RX = *ADDR Written as "LOAD RX, ADDR"
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B STORE RY, ADDR *ADDR = RY Written as "STORE ADDR, RY"
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C BREQ RX, RY, ADDR if (RX == RY) IP = ADDR
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D BRNEQ RX, RY, ADDR if (RX != RY) IP = ADDR
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E CLEQ RX, RY, ADDR if (RX == RY) {RP -= 2; *RP = IP; IP = ADDR}
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F CLNEQ RX, RY, ADDR if (RX != RY) {RP -= 2; *RP = IP; IP = ADDR}
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Assembly Language
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-----------------
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Lines of assembly are of the following form:
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LABEL: OPER ARG1, ARG2, ARG3 ;Comment
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The language is case-insensitive and uses hexadecimal numbers. A label
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can consist of any alphanumeric characters as long as it is not
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interpretable as a hexadecimal number. The label, instruction, and
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comment elements are all optional, as is spacing between the arguments.
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For the arguments of each instruction see the previous section.
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Address arguments can be either absolute addresses or references to or
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relative to a label. Relative references are of the form LABEL +/- N;
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the spacing is optional.
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In addition to the true instructions there are three
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pseudo-instructions. ORG sets the location of the following code and
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data; as it has no direct equivalent in machine code it cannot have a
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label. The default starting address of 0 does not need to be indicated
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with ORG. DATA introduces a byte of data. ADDR introduces two bytes of
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data containing the address of a reference to or relative to a label.
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Boot
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----
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At boot the initial program loader (IPL) loads a program to RAM starting
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at address 0 after which is cedes control to the CPU. If an
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implementation has a front panel the IPL is optional. The instruction
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and return pointers are initialised as 0 and the first address after RAM
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respectively, while other registers and RAM are uninitialised.
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Emulator and Device Control Programs
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------------------------------------
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Usage:
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* emulator (-v) program (2> verbose_output)
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* tapectl (-r tape) (-p tape)
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* floppyctl (-0 disc) (-1 disc)
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* modemctl -o/[-a address:port]/[-d address:port]/-h
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By default the emulator runs at roughly 500 KIPS and has 2 KiB of RAM.
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The arguments -dRAM4, -dRAM8, -dRAM16, -dRAM32, and -dRAM64 can be used
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to compile the emulator with 4, 8, 16, 32, or 64 KiB (minus the reserved
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addresses) of RAM respectively instead and the speed limitations can be
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removed with the argument -dfast. When run with the argument -v the
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current state of the registers is output to stderr before each
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instruction.
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Input and output are handled by an emulated roughly 1000 CPS
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ASCII-compatible glass teletype terminal with local echo on by default.
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Of the control characters bell (^G), backspace (^H), line feed (^J),
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carriage return (^M), and device control characters two (^R) and four
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(^T) are used by the terminal: the device control characters are used to
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turn the local echo on and off respectively while the rest have their
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standard uses. The backspace and delete keys input their respective
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characters and non-character keys null.
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In Linux the emulator can be compiled with support for a character
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printer, an emulated high speed 8-bit paper tape reader and punch, an
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emulated two-drive 8" floppy disc system, a modem, and an input status
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register with the arguments -dprinter, -dtape, -dfloppy, -dmodem, and
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-dstatus respectively. Full 64 KiB of RAM and all of these options can
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also be enabled with the argument -dfull. The printer is mapped to
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address FFFE, the tape reader and punch to FFFD, the disc system to FFFB
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and FFFC, the modem to FFF9 and FFFA, and the input status register to
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FFF8.
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The printer prints into /dev/usb/lp0. The tape files read from and
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punched to are (re)set using the program tapectl with the arguments -r
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and -p respectively and the disc files in drives 0 and 1 using the
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program floppyctl with the arguments -0 and -1 respectively. The disc
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system uses hard sectored single-sided discs with 77 tracks of 32
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sectors of 137 bytes, or 337568 bytes in total: the disc files must be
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of this size. The modem is controlled by the program modemctl: the
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options -o and -a are used to set the originate and answer modes, the
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latter with the address and port to be listened; -d to dial an address
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and port to be called; and -h to hang. Dialing when in answer mode
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automatically switches the modem to originate mode. The modem hangs
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automatically if the connection is lost or hanged from the other side,
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if another address and port are dialed, if a mode change command is
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given, or if the emulator is halted.
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The floppy disc system uses two ports: command at FFFB and data at FFFC.
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Only the low nibble of the command port is used, consisting of a
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three-bit command followed by a one-bit drive number used as an argument
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by instructions 1 and 4-7. The track or sector to be accessed is input
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to and the buffer accessed sequentially through the data port after the
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relevant command is input to the command port. New commands other than
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resetting the system are ignored until the current command is fully
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executed. Note that each sector begins with a synchronisation bit that
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must always be set.
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The commands for the disc system are:
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0: Reset the system.
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1: Format a disc.
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2: Read a sector from the buffer to the computer.
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3: Write a sector from the computer to the buffer.
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4: Set the track to be accessed.
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5: Set the sector to be accessed.
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6: Read a sector from a disc to the buffer.
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7: Write a sector from the buffer to a disc.
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The modem also uses two ports: status at FFF9 and data at FFFA. Only the
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least significant bit of the status port is used, indicating whether
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the modem is connected or not. Unsetting the bit hangs the modem while
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setting it in answer mode hangs any current call and listens for an
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incoming call to answer. Setting the bit in originate mode is ignored.
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The input status register can be used to check if a device is ready to
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be read from. The reserved addresses FFF8-FFFF are mapped to the bits
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7-0: a set bit means either that the device is ready or that no input
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device is mapped to the address in question.
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The IPL loads the program specified as an argument when running the
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emulator.
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Assembler and Disassembler
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--------------------------
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Usage:
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* assembler program (< input)
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* disassembler program (> output)
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Both the assembler and the disassembler are run with a program as their
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sole argument: they take their input from and print their output to
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stdin and stdout respectively.
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An initial gap created with ORG is not included in an assembled program.
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All possible interpretations of a disassembled program are included in
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its listing, resulting in overlapping information.
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Changelog
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---------
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v2.0
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* Added the ability to shift a register multiple steps in one
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instruction
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* Changed the register argument of STORE from RX to RY
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* Added support for an emulated floppy disc system and modem and an
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input status register to the emulator
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* Added the ability to use ORG non-initially to the assembler
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* Changed tapectl so that it uses arguments for input
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v1.0
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* Initial release
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