crazyettin
/
Thingamajig
1
0
Fork 0
Code Issues Pull Requests Projects Releases 2 Wiki Activity

Fix the return address stack so it can handle 16-bit addresses, remove an unused library from the disassembler code, and tidy up the disassembler code and the readme a bit

This commit is contained in:
CrazyEttin 2022-07-27 17:11:09 +03:00
parent ddce9abba1
commit bbb2a1a695
3 changed files with 35 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
disassembler.pas
View File

@ -1,6 +1,6 @@
program Disassembler;
uses Crt, Sysutils;
uses Sysutils;
var
Op, Regs: 0 .. $f; //Opcode, and register arguments in a single variable
@ -90,16 +90,13 @@ begin
write (Opcodes [Op]);
if Op = $b then writeln (IntToHex (Addr, 1), ', R', X)
else begin
if Op >= 2 then if Op <> $b then write ('R', X);
if Op >= 2 then write ('R', X);
if Op >= 6 then if Op <= 9 then write (', R', Y);
if OP >= $c then write (', R', Y);
if Op >= $a then write (', ', IntToHex (Addr, 1));
writeln ();
end;
until (BP >= EP);
end.

24
emulator.pas
View File

@ -56,10 +56,12 @@ begin
if IP > $ffef then break;
//Address argument
if Op >= $a then begin
//High byte
Addr := Mem [IP];
Addr := Addr shl 8;
IP := IP + 1;
if IP > $ffef then break;
//Low byte
Addr := Addr + Mem [IP];
IP := IP + 1;
if IP > $ffef then break;
@ -70,7 +72,13 @@ begin
if Op = 0 then Halt := 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 break;
//Low byte of the return address
IP := IP + Mem [RP];
RP := RP + 1;
if RP > $fff0 then break;
end
@ -122,9 +130,15 @@ begin
//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 break;
Mem [RP] := IP;
Mem [RP] := IP and $ff;
//High byte of the return address
RP := RP - 1;
if RP > $fff0 then break;
Mem [RP] := IP shr 8;
//Call
IP := Addr;
if IP > $ffef then break;
end;
@ -132,9 +146,15 @@ begin
//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 break;
Mem [RP] := IP;
Mem [RP] := IP and $ff;
//High byte of the return address
RP := RP - 1;
if RP > $fff0 then break;
Mem [RP] := IP shr 8;
//Call
IP := Addr;
if IP > $ffef then break;
end;

23
readme.md
View File

@ -1,7 +1,7 @@
Thingamajig
===========
Thingamajig is a RISC-y and MISC-y hobbyist computer architecture. Its
Thingamajig is a RISC-y and MISC-y homebrew computer architecture. Its
git repository can be found at
https://ahti.space/git/crazyettin/Thingamajig.
@ -14,10 +14,10 @@ Registers and Memory
* 8-bit memory addresses 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 the
reserved addresses. The instruction and return pointers are initialised
as 0 and FFF0 respectively; other registers and memory are unitialised.
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.
Instructions
------------
@ -27,7 +27,7 @@ Instructions without an address argument are 8-bit and those with one
modified.
0 HALT
1 RET IP = *RP; RP += 1
1 RET IP = *RP; RP += 2
2 SHL RX RX <<= 1 Logical shifts
3 SHR RX RX >>= 1
@ -46,15 +46,14 @@ B STORE RX, ADDR *ADDR = RX Written as "STORE ADDR, RX" in
C BREQ RX, RY, ADDR if (RX == RY) IP = ADDR
D BRNEQ RX, RY, ADDR if (RX != RY) IP = ADDR
E CLEQ RX, RY, ADDR if (RX == RY) {RP -= 1; *RP = IP; IP = ADDR}
F CLNEQ RX, RY, ADDR if (RX != RY) {RP -= 1; *RP = IP; IP = ADDR}
E CLEQ RX, RY, ADDR if (RX == RY) {RP -= 2; *RP = IP; IP = ADDR}
F CLNEQ RX, RY, ADDR if (RX != RY) {RP -= 2; *RP = IP; IP = ADDR}
Memory-Mapped Devices
---------------------
Input (when read from) and output (when written to) are mapped to
address FFFF. The emulator implements this by emulating a dumb serial
terminal.
address FFFF. The emulator emulates a dumb terminal for this.
Arbitrary devices can be mapped to the other reserved addresses.
@ -62,5 +61,5 @@ Initial Program Loader
----------------------
At boot the initial program loader loads a program to the memory
starting from address 0 after which is cedes control to the processor.
The emulator loads the program from a file.
starting from address 0 after which is cedes control to the CPU. The
emulator loads the program from a file.