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Format/typo check 2013/cable3

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Cody Boone Ferguson committed 2023-12-03 10:22:47 -08:00
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@@ -69,6 +69,7 @@ Update: This entry now has its own website:
## Author's remarks:
### A tiny but highly functional PC emulator/virtual machine
The author hereby presents, for the delectation (?) of the judges, a portable PC
@@ -100,6 +101,7 @@ machine, and you will get an emulation of a big endian 8086, a rather bizarre
and somewhat useless beast. For everyone else, please run the emulator on a
little endian machine.
### RULE 2 ABUSE DISCLAIMER
- [cable3.c](cable3.c) is 4043 bytes in length (half an 8086).
@@ -145,6 +147,7 @@ occasionally go overboard with nasty nested indexes to give things like this:
- This entry might result in an adjustment to the IOCCC size tool for the 2014
competition (see above).
### Compiling on different platforms
This entry has been tested on Windows (compiled with MS Visual Studio 2010 and
@@ -168,6 +171,7 @@ KB=(kb=H(8),kbhit())&&(r[1190]=getch(),H(7))
NOTE: this is done in the [Alternate code](#alternate-code).
### POSIX portability note
The code as supplied uses implicit function declarations for POSIX file I/O and
@@ -204,7 +208,7 @@ See the [runme](runme) script.
## To use the emulator - floppy mode only
The simplest use of the emulator is with a single floppy boot disk image, like
the fd.img provided, which is a FreeDOS boot disk.
the `fd.img` provided, which is a FreeDOS boot disk.
Before running the emulator on a Unix-type system, `stty` needs to be used to
put the keyboard into raw mode (and afterwards it needs to be put back to
@@ -240,9 +244,10 @@ an easy way to copy files and programs to and from the disk image. Or, you can
install programs from regular floppy disk images (see [Floppy disk
support](#floppy-disk-support) below).
### Keyboard emulation
The emulator simulates an XT-style keyboard controlled by an Intel 8042 chip on
The emulator emulates an XT-style keyboard controlled by an Intel 8042 chip on
I/O port 0x60, generating IRQ1 and then interrupt 9 on each key press. This is
harder than it sounds because a real 8042 returns scan codes rather than the
ASCII characters which the C standard I/O functions return. Rather than make the
@@ -257,8 +262,8 @@ example, with non-QWERTY e.g. international keyboards.
Most of the time you can just type normally, but there are special sequences to
get `Alt+xxx` and `Fxxx`.
To send an `Alt+XXX` key combination, press (`^A` or `Ctrl+A`) then the key, so for example to
type `Alt+F`, press (`^A` / `Ctrl+A`) then `F`.
To send an `Alt+XXX` key combination, press (`^A` or `Ctrl+A`) then the key, so
for example to type `Alt+F`, press (`^A` / `Ctrl+A`) then `F`.
To send an `Fxx` key, press `^F` / `Ctrl+F` then a number key. For example, to
get the `F4` key, press `^F` / `Ctrl+F` then `4`. To get `F10`, press `^F` /
@@ -268,6 +273,7 @@ To send a `Page Down` key, press `^F` / `Ctrl+F` then `O` (letter O, not digit
zero). To send a `Page Up` key, press `^F` / `Ctrl+F` then `E`. Other key
combinations are left for the discovery of the user.
### Text mode support
The emulator supports both text output via the standard BIOS interrupt 0x10
@@ -295,6 +301,7 @@ state which confuses the emulator, resulting in subsequent text output being
invisible. If this happens, just use the DOS `CLS` command to clear the screen
and all will be well again.
### Graphics mode support
[Hercules 720x348 monochrome graphics
@@ -314,6 +321,7 @@ little odd but you will get used to it).
On Unices, SDL will automatically output graphics via X11 if the DISPLAY
environment variable is set up.
### Dual graphics card support
Some applications (e.g. AutoCAD) support a PC configuration with a CGA card and
@@ -321,6 +329,7 @@ a Hercules card, for simultaneous text and graphics output on different
displays. The emulator simulates this configuration, too, using separate windows
for the (terminal) text and (SDL) graphics displays.
### BIOS
Like a real PC, the emulator needs a BIOS to do anything useful. Here we use a
@@ -333,6 +342,7 @@ clock and so on, much as a "real" PC BIOS does, and also a small
timer-controlled video driver to convert video memory formatting into ANSI
escape sequences when the emulator is in text mode.
### CPU and memory emulation
Memory map is largely as per a real PC, with interrupt vector table at `0:0`,
@@ -343,22 +353,23 @@ memory-mapped (at `F000:0`), which enables considerable optimisation of the
emulator's instruction execution unit by permitting the unification of memory
and register operations, while remaining invisible to the running software.
CPU supports the full 8086/186 instruction set. Due to the complexities of the
8086's arbitrary-length instruction decoding and flags, 8086 instructions are
first converted to a simpler intermediate format before being executed. This
The CPU supports the full 8086/186 instruction set. Due to the complexities of
the 8086's arbitrary-length instruction decoding and flags, 8086 instructions
are first converted to a simpler intermediate format before being executed. This
conversion, along with instruction lengths and how each instruction modifies the
flags, is assisted by some lookup tables which form part of the BIOS binary.
The CPU also implements some "special" two-byte opcodes to help the emulator talk with the outside world. These are:
The CPU also implements some "special" two-byte opcodes to help the emulator
talk with the outside world. These are:
- `0F 00` - output character in register AL to terminal.
- `0F 00` - output character in register `AL` to terminal.
- `0F 01` - write real-time clock data (as returned by `localtime()`) to memory
location `ES:BX`.
- `0F 02` - read AX bytes from disk at offset `512*(16*SI+BP)` into memory
- `0F 02` - read `AX` bytes from disk at offset `512*(16*SI+BP)` into memory
location `ES:BX`. Disk is specified in `DL` (`0` = hard disk, `1` = floppy
disk).
- `0F 03` - write AX bytes at memory location `ES:BX` to disk at offset
- `0F 03` - write `AX` bytes at memory location `ES:BX` to disk at offset
`512*(16*SI+BP)`. Disk is specified in `DL` as per `0F 02`.
Emulator exit is triggered if `CS:IP == 0:0` (which would be nonsensical in real
@@ -367,6 +378,7 @@ software since this is where the interrupt vector table lives). The supplied
`JMP 0:0` instruction, to allow the user to easily quit the emulator without
shutting down the terminal.
### Floppy disk support
Emulates a 3.5" high-density floppy drive. Can read, write and format 1.44MB
@@ -378,6 +390,7 @@ e.g. [Vetusware](https://vetusware.com)), the easiest way to "change disks" is
to copy each disk image in turn over the floppy image file you specify on the
command line. Don't forget to put your original boot disk back at the end!
### Hard disk support
Supports up to 1023 cylinders, 63 sectors per track, 63 heads for disks up to
@@ -397,16 +410,19 @@ Note that unlike a real PC, the emulator cannot boot from a hard disk (image).
Therefore, you will always need to use a bootable floppy image, even if after
boot everything runs from the HD.
### Mouse
No mouse is emulated.
### Real-time clock
Reading the [RTC](https://en.wikipedia.org/wiki/Real-time_clock) (both time and
date) is emulated via the standard BIOS clock interface, pulling the time/date
from the host computer. Setting the time or date is not supported.
### Timers
A countdown timer on I/O port `0x40` is simulated in a broken way which is good
@@ -419,10 +435,12 @@ On a real PC, IRQ 0 and interrupt 8 are fired every 55ms. The emulator tries to
do the same but again, the delay period is not calibrated so you get what you
get.
### PC speaker
Beeps only, through the console.
### Software supported
The emulator will run practically any software a real PC (of the spec listed at