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Remove limits on the pointer values, specify access to unused addresses and modify instruction fetching and calling to take into account unused addresses and memory mapped devices in the emulator, and write a separate section for the emulator in the readme

This commit is contained in:
CrazyEttin 2022-08-26 14:36:42 +03:00
parent 3eba71ab0e
commit 6d14b9a5bf
2 changed files with 247 additions and 281 deletions
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398
emulator.pas
View File

@ -16,6 +16,7 @@ type
const
IO = $ffff;
LastRAM = $ffef;
var
Hlt, ASCII, Verbose: boolean; //Halt, ASCII, and verbose flags
@ -23,7 +24,7 @@ var
X, Y: 0 .. 3; //Register arguments
Addr, IP, RP: word; //Immediate or address argument and instruction and return pointers
R: array [0 .. 3] of byte; //General-purpose registers
Mem: array [0 .. $ffef] of byte; //Memory
Mem: array [0 .. LastRAM] of byte; //Random access memory
Prog{$ifdef printer}, Prn{$endif}{$ifdef tape}, TapeIn, TapeOut{$endif}: file of byte; //Program file, line printer, and tape reader and punch tapes
{$ifdef tape}
Reader, Punch: Tape; //States of the tape reader and punch
@ -31,6 +32,7 @@ var
{$endif}
Ch, Scan: ansichar; //Character for input and output and scancode for non-ASCII keys
IC, LFX: integer; //Instruction counter for CPU speed
Fetched: byte; //Fetched byte
//Terminal output
procedure Output;
@ -60,161 +62,13 @@ begin
IC := 0;
end;
//Load a byte from memory
function LoadByte (W: word): byte;
var
B: byte;
begin
//Initialise the halt flag, the pointers, and the instruction counter
Hlt := false;
IP := 0;
RP := $fff0;
IC := 0;
//Initialise the tape reader and punch
{$ifdef tape}
Reader.Path := '';
Reader.Reset := true;
Reader.Pos := 0;
Punch.Path := '';
Punch.Reset := true;
Punch.Pos := 0;
{$endif}
//Check the arguments
if ParamCount = 0 then begin
writeln ('Usage: emulator (-v) program (2> verbose_output)');
halt;
end;
if ParamStr (1) = '-v' then begin
Verbose := true;
if ParamCount <> 2 then begin
writeln ('Usage: emulator (-v) program (2> verbose_output)');
halt;
end;
end
else begin
Verbose := false;
if ParamCount <> 1 then begin
writeln ('Usage: emulator (-v) program (2> verbose_output)');
halt;
end;
end;
//Read a program file and check for errors
{$i-}
if Verbose = true then assign (Prog, ParamStr (2))
else assign (Prog, ParamStr (1));
reset (Prog);
{$i+}
if IOResult <> 0 then begin
writeln ('Error: program file cannot be read from');
halt;
end;
repeat
read (Prog, Mem [IP]);
IP := IP + 1;
until (eof (Prog)) or (IP = $fff0);
if IP = $fff0 then begin
writeln ('Error: memory overflow');
halt;
end;
//Reinitialise the instruction pointer
IP := 0;
//Begin the main loop
while Hlt = false do begin
//Print the CPU state to StdErr
if Verbose = true then writeln (StdErr, 'IR: ', IntToHex (Op, 1), IntToHex (Regs, 1), IntToHex (Addr, 4), '; IP: ', IntToHex (IP, 4), ', RP: ', IntToHex (RP, 4), '; R0: ', IntToHex (R[0], 2), ', R1: ', IntToHex (R[1], 2), ', R2: ', IntToHex (R[2], 2), ', R3: ', IntToHex (R[3], 2), ansichar ($d));
//Fetch the instruction and increment the instruction pointer
//Opcode
Op := Mem [IP] and $f0 shr 4;
//Register arguments
Regs := Mem [IP] and $f;
X := Mem [IP] and $c shr 2;
Y := Mem [IP] and 3;
IP := IP + 1;
if IP > $ffef then begin
writeln ('Error: illegal instruction pointer value');
halt;
end;
//Immediate or address argument
if Op >= $a then begin
//Immediate or high byte of address
Addr := Mem [IP];
Addr := Addr shl 8;
IP := IP + 1;
if IP > $ffef then begin
writeln ('Error: illegal instruction pointer value');
halt;
end;
//Low byte of address
if Op = $a then begin
if Y = 0 then begin
Addr := Addr + Mem [IP];
IP := IP + 1;
if IP > $ffef then begin
writeln ('Error: illegal instruction pointer value');
halt;
end;
end;
end
else begin
Addr := Addr + Mem [IP];
IP := IP + 1;
if IP > $ffef then begin
writeln ('Error: illegal instruction pointer value');
halt;
end;
end;
end
else Addr := 0;
//Decode and execute the instruction
//Halt
if Op = 0 then Hlt := true
//Ret
else if Op = 1 then begin
//High byte of the return address
IP := Mem [RP];
IP := IP shl 8;
RP := RP + 1;
if RP > $fff0 then begin
writeln ('Error: illegal return pointer value');
halt;
end;
//Low byte of the return address
IP := IP + Mem [RP];
RP := RP + 1;
if RP > $fff0 then begin
writeln ('Error: illegal return pointer value');
halt;
end;
end
//Shl
else if Op = 2 then R [X] := R [X] shl 1
//Shr
else if Op = 3 then R [X] := R [X] shr 1
//Rol
else if Op = 4 then R [X] := RolByte (R [X])
//Ror
else if Op = 5 then R [X] := RorByte (R [X])
//Nand
else if Op = 6 then R [X] := not (R [X] and R [Y])
//And
else if Op = 7 then R [X] := R [X] and R [Y]
//Or
else if Op = 8 then R [X] := R [X] or R [Y]
//Xor
else if Op = 9 then R [X] := R [X] xor R [Y]
//Load
else if Op = $a then begin
//Immediate
if Y <> 0 then R [X] := Addr shr 8
//Address
else begin
//Terminal input
if Addr = IO then begin
if W = IO then begin
wait;
//Read a keypress
repeat
@ -257,11 +111,11 @@ begin
end;
//Process the keypress
Output; //Local echo
R [X] := byte (Ch);
B := byte (Ch);
end
//Tape reader
{$ifdef tape}
else if Addr = $fffd then begin
else if W = $fffd then begin
wait;
assign (State, ExpandFileName ('~/.tapes.thingamajig'));
//Check the reader state
@ -279,11 +133,11 @@ begin
try
reset (TapeIn);
seek (TapeIn, Reader.Pos);
read (TapeIn, R [X]);
read (TapeIn, B);
close (TapeIn);
Reader.Pos := Reader.Pos + 1;
except
R [X] := $ff;
B := $ff;
end;
//Save the reader state
if FileExists (ExpandFileName ('~/.tapes.thingamajig')) then begin
@ -297,26 +151,30 @@ begin
end;
end
{$endif}
//Unused addresses
else if W > LastRAM then B := 0
//Regular load
else R [X] := Mem [Addr];
end;
end
//Store
else if Op = $b then begin
else B := Mem [W];
//Result
LoadByte := B;
end;
procedure StoreByte (W: word; B: byte);
begin
//Terminal output
if Addr = IO then begin
if W = IO then begin
wait;
Ch := ansichar (R [Y]);
Ch := ansichar (B);
Output;
end
//Printer
{$ifdef printer}
else if Addr = $fffe then begin
else if W = $fffe then begin
wait;
assign (Prn, '/dev/usb/lp0');
try
rewrite (Prn);
write (Prn, R [Y]);
write (Prn, B);
close (Prn);
except
end;
@ -324,7 +182,7 @@ begin
{$endif}
//Tape punch
{$ifdef tape}
else if Addr = $fffd then begin
else if W = $fffd then begin
wait;
assign (State, ExpandFileName ('~/.tapes.thingamajig'));
//Check the punch state
@ -343,7 +201,7 @@ begin
if FileExists (Punch.Path) = false then begin
try
rewrite (TapeOut);
write (TapeOut, R [Y]);
write (TapeOut, B);
close (TapeOut);
Punch.Reset := false;
except
@ -352,7 +210,7 @@ begin
else if Punch.Reset then begin
try
rewrite (TapeOut);
write (TapeOut, R [Y]);
write (TapeOut, B);
close (TapeOut);
Punch.Reset := false;
except
@ -362,7 +220,7 @@ begin
try
reset (TapeOut);
seek (TapeOut, FileSize (TapeOut));
write (TapeOut, R [Y]);
write (TapeOut, B);
close (TapeOut);
except
end;
@ -381,8 +239,158 @@ begin
end
{$endif}
//Regular store
else Mem [Addr] := R [Y];
else if W <= LastRAM then Mem [W] := B;
end;
procedure Call;
begin
//Low byte of the return address
RP := RP - 1;
StoreByte (RP, IP and $ff);
//High byte of the return address
RP := RP - 1;
StoreByte (RP, IP shr 8);
//Call
IP := Addr;
end;
begin
//Initialise the halt flag, the pointers, and the instruction counter
Hlt := false;
IP := 0;
RP := LastRAM + 1;
IC := 0;
//Initialise the tape reader and punch
{$ifdef tape}
Reader.Path := '';
Reader.Reset := true;
Reader.Pos := 0;
Punch.Path := '';
Punch.Reset := true;
Punch.Pos := 0;
{$endif}
//Check the arguments
if ParamCount = 0 then begin
writeln ('Usage: emulator (-v) program (2> verbose_output)');
halt;
end;
if ParamStr (1) = '-v' then begin
Verbose := true;
if ParamCount <> 2 then begin
writeln ('Usage: emulator (-v) program (2> verbose_output)');
halt;
end;
end
else begin
Verbose := false;
if ParamCount <> 1 then begin
writeln ('Usage: emulator (-v) program (2> verbose_output)');
halt;
end;
end;
//Read a program file and check for errors
{$i-}
if Verbose = true then assign (Prog, ParamStr (2))
else assign (Prog, ParamStr (1));
reset (Prog);
if FileSize (Prog) > LastRAM + 1 then begin
writeln ('Error: program size cannot exceed ', LastRam + 1, ' bytes');
halt;
end;
{$i+}
if IOResult <> 0 then begin
writeln ('Error: program file cannot be read from');
halt;
end;
repeat
read (Prog, Mem [IP]);
IP := IP + 1;
until (eof (Prog));
//Reinitialise the instruction pointer
IP := 0;
//Begin the main loop
while Hlt = false do begin
//Print the CPU state to StdErr
if Verbose = true then writeln (StdErr, 'IR: ', IntToHex (Op, 1), IntToHex (Regs, 1), IntToHex (Addr, 4), '; IP: ', IntToHex (IP, 4), ', RP: ', IntToHex (RP, 4), '; R0: ', IntToHex (R[0], 2), ', R1: ', IntToHex (R[1], 2), ', R2: ', IntToHex (R[2], 2), ', R3: ', IntToHex (R[3], 2), ansichar ($d));
//Fetch the instruction and increment the instruction pointer
//Fetch the opcode and register arguments
Fetched := LoadByte (IP);
//Decode the opcode
Op := Fetched and $f0 shr 4;
//Decode the register arguments
Regs := Fetched and $f;
X := Fetched and $c shr 2;
Y := Fetched and 3;
IP := IP + 1;
//Immediate or address argument
if Op >= $a then begin
//Immediate or high byte of address
Fetched := LoadByte (IP);
Addr := Fetched;
Addr := Addr shl 8;
IP := IP + 1;
//Low byte of address
if Op = $a then begin
if Y = 0 then begin
Fetched := LoadByte (IP);
Addr := Addr + Fetched;
IP := IP + 1;
end;
end
else begin
Fetched := LoadByte (IP);
Addr := Addr + Fetched;
IP := IP + 1;
end;
end
else Addr := 0;
//Decode and execute the instruction
//Halt
if Op = 0 then Hlt := true
//Ret
else if Op = 1 then begin
//High byte of the return address
IP := LoadByte (RP);
IP := IP shl 8;
RP := RP + 1;
//Low byte of the return address
IP := IP + LoadByte (RP);
RP := RP + 1;
end
//Shl
else if Op = 2 then R [X] := R [X] shl 1
//Shr
else if Op = 3 then R [X] := R [X] shr 1
//Rol
else if Op = 4 then R [X] := RolByte (R [X])
//Ror
else if Op = 5 then R [X] := RorByte (R [X])
//Nand
else if Op = 6 then R [X] := not (R [X] and R [Y])
//And
else if Op = 7 then R [X] := R [X] and R [Y]
//Or
else if Op = 8 then R [X] := R [X] or R [Y]
//Xor
else if Op = 9 then R [X] := R [X] xor R [Y]
//Load
else if Op = $a then begin
//Immediate
if Y <> 0 then R [X] := Addr shr 8
//Address
else R [X] := LoadByte (Addr);
end
//Store
else if Op = $b then StoreByte (Addr, R [Y])
//Breq
else if Op = $c then begin
if R [X] = R [Y] then IP := Addr;
@ -393,53 +401,11 @@ begin
end
//Cleq
else if Op = $e then begin
if R [X] = R [Y] then begin
//Low byte of the return address
RP := RP - 1;
if RP > $fff0 then begin
writeln ('Error: illegal return pointer value');
halt;
end;
Mem [RP] := IP and $ff;
//High byte of the return address
RP := RP - 1;
if RP > $fff0 then begin
writeln ('Error: illegal return pointer value');
halt;
end;
Mem [RP] := IP shr 8;
//Call
IP := Addr;
if IP > $ffef then begin
writeln ('Error: illegal instruction pointer value');
halt;
end;
end;
if R [X] = R [Y] then Call;
end
//Clneq
else if Op = $f then begin
if R [X] <> R [Y] then begin
//Low byte of the return address
RP := RP - 1;
if RP > $fff0 then begin
writeln ('Error: illegal return pointer value');
halt;
end;
Mem [RP] := IP and $ff;
//High byte of the return address
RP := RP - 1;
if RP > $fff0 then begin
writeln ('Error: illegal return pointer value');
halt;
end;
Mem [RP] := IP shr 8;
//Call
IP := Addr;
if IP > $ffef then begin
writeln ('Error: illegal instruction pointer value');
halt;
end;
end;
if R [X] <> R [Y] then Call;
end;
//Increment the instruction counter

52
readme.md
View File

@ -14,12 +14,6 @@ assembler and a disassembler, all written in FreePascal. It also
includes couple of simple example programs for Thingamajig written in
Assembly.
Speed
-----
Thingamajig does not have a prescribed speed. The emulator runs at
roughly 500 KIPS.
Registers and Memory
--------------------
@ -28,11 +22,10 @@ Registers and Memory
* 8-bit general-purpose registers R0-R3
* 8-bit memory locations 0-FFFF
Multi-byte values are big-endian. Memory addresses FFF0-FFFF are
reserved for memory mapped devices; the instruction and return pointers
cannot have values higher than FFEF and FFF0 respectively to avoid them.
The instruction and return pointers are initialised as 0 and FFF0
respectively, while other registers and memory are unitialised.
Multi-byte values are big-endian. Memory locations 0-FFEF are used for
RAM while FFF0-FFFF are reserved for memory mapped devices. Input and
output are mapped to address FFFF, while arbitrary devices can be mapped
to the other reserved addresses.
Instructions
------------
@ -78,8 +71,7 @@ For the arguments of each instruction see the previous section.
Address arguments can be either absolute addresses or references to or
relative to a label. Relative references are of the form LABEL +/- N,
the spacing being optional. Note that the assembler does not check for
addresses or references to reserved addresses.
the spacing being optional.
In addition to the true instructions there are three
pseudo-instructions. ORG defines the starting address of the program: it
@ -88,26 +80,34 @@ not required if the starting address is 0. DATA introduces a byte of
data. ADDR introduces two bytes of data containing the address of a
reference to or relative to a label.
Memory-Mapped Devices
---------------------
Boot
----
Input and output are mapped to address FFFF; the emulator emulates a
roughly 1000 CPS glass teletype with local echo.
At boot the initial program loader (IPL) loads a program to the RAM
starting at address 0 after which is cedes control to the CPU. The
instruction and return pointers are initialised as 0 and the first
address after RAM respectively, while other registers and RAM are
uninitialised.
Arbitrary devices can be mapped to the other reserved addresses.
Emulator
--------
The emulator runs at roughly 500 KIPS and has the full 65520 bytes of
RAM.
Input and output are handled by an emulated roughly 1000 CPS glass
teletype terminal with local echo. Note that of the control characters
only bell, backspace, line feed, and carriage return are used by the
terminal, and the backspace and delete keys are tied to their respective
characters and non-character keys to null.
In Linux the emulator can be compiled with support for a character
printer and an emulated punched tape reader and punch with the arguments
-dprinter and -dtape respectively. The printer is mapped to address FFFE
and the tape reader and punch to FFFD. The printer prints into
/dev/usb/lp0 and the tape files read from and punched to are (re)set
using the program tapectl. If you wish to use a different setup you have
to modify the code yourself.
using the program tapectl.
Initial Program Loader
----------------------
At boot the initial program loader (IPL) loads a program to the memory
starting from address 0 after which is cedes control to the CPU. The
emulator loads the program from a ROM file.
The IPL loads a program from a file specified when launching the
emulator.