A MIX emulator. Slightly off-spec. I/O devices are:
| Number | Type | Filename (read) | Filename (write) |
|---|---|---|---|
| 0-7 | Magnetic tape | tape[0-7].dev |
tape[0-7].dev |
| 8-15 | Hard drive | disk[0-7].dev |
disk[0-7].dev |
| 16 | Card reader | card.dev |
|
| 17 | Card punch | punch.dev |
|
| 18 | Printer | printer.dev |
|
| 19 | Terminal | (stdin) |
(stdout) |
| 20 | Paper tape | paper.dev |
tapep.dev |
I/O is asynchronous, using <pthread.h>.
There is a negative address space.
All attempts to access it from positive addresses (including jumps) access instead address 0.
When an I/O action starts from a negative address,
its completion causes an interrupt unless a JBUS has occured on that device in the meantime from a negative address.
Use JRED *+2; JMP X instead of JBUS X, but only if address is negative.
Interrupts occur as described in Knuth.
The floating-point handling is NOT to spec.
We support both one and two word floats. Both are IEEE 754 binary; exponents are 6 or 12 bits long, respectively.
Floating-point tests are J-, JF*, JD* (double-precision, joint rA and rX),
JG* (tests floating point in rX), FCMP, GCMP, and DCMP.
FP arithmetic includes FADD, DADD, FSUB, DSUB, FMUL, DMUL, FDML, FDIV, DDIV, and DFDV.
FDML multiplies F by the float in memory and stores it in D;
DFDV divides D by the float in memory and stores it in F, leaving rX alone.
When do we jump?
- |
* |
If positive/greater than | If zero/equal | If negative/less than | If NaN |
|---|---|---|---|---|---|
L |
N |
√ | |||
E |
Z |
√ | |||
G |
P |
√ | √ | ||
GE |
PZ |
√ | √ | ||
NE |
NZ |
√ | √ | √ | |
LE |
ZN |
√ | √ | ||
CMP |
RE |
√ | √ | √ | |
NGE |
IN |
√ | √ | ||
NGL |
IZ |
√ | √ | ||
NLE |
IP |
√ | √ | ||
NL |
NN |
√ | √ | √ | |
GL |
PN |
√ | √ | ||
NG |
NP |
√ | √ | √ | |
NC |
NR |
√ |
For conditional jumps that save J, replace the J
at the beginning by B.
Bytes are 6 bits.
The assembler is exactly to spec. This means that the format is fixed.
It outputs code that can be loaded in to the card reader.
With slight changes in mixal.c (in print_preamble, move the newline to after the CA. (JAZ 0,3),
change the first, second, and fifth lines to M [6, Y [6, and D [4 (IN 14(20), IN 28(20) and JBUS 4(20)),
and change all the 7s in print_hunk to 5s) the code becomes loadable onto paper tape, instead.
To modify the emulator to act (at least when booting) as if there is no card reader, it suffices to change the input(memp, 0, 16); while(!ready(16)); in main (mix_cpu.c) by replacing the 16 with 20.
The standard "MIXCII" characters Θ, Φ, and Π are replaced by tilde and open and close brackets.
A final set of eight characters is appended to the end of MIXCII, thus rendering the entire character set
ABCDEFGHI~JKLMNOPQR[]STUVWXYZ0123456789.,()+-*/=$<>@;:'`\"&{}|^.
On input to the computer, lowercase letters are capitalized.
The assembler also works in MIXCII.
One further addition is that J is treated as I7 for purposes of indexing.
This allows return-from-leaf-subroutine to be done with a JMP 0,7,
obviating some of the need for self-modifying code.