# Running CALC.COM under FreeDOS in QEMU

This is the manual FreeDOS route.  The supported, tested path remains
`shell/tests/calc_cli.py`, which boots the compiler's own `bootcom.s` loader.

## 1. Build CALC.COM

From the repository root:

```sh
cd shell

# Build comtest (also runs the normal COM tests).
tests/run_com_tests.sh

# Stage CALC.PAS with CALC.INC beside it.
tests/calc_ladder.sh

# Compile the staged source.  comtest writes CALC.PAS.COM in the cwd.
printf '%s\n' ../tmp/calc_ladder/CALC.PAS | ./comtest
mv -f CALC.PAS.COM CALC.COM
```

If a fresh `CALC.PAS.COM` is already present, `cp CALC.PAS.COM CALC.COM` is
enough.

## 2. Make a FAT floppy image containing CALC.COM

```sh
sudo apt install qemu-system-x86 mtools unzip

cd /tmp
dd if=/dev/zero of=calc.img bs=1024 count=1440
mformat -i calc.img -f 1440 ::
mcopy -i calc.img /path/to/TP3-comp/shell/CALC.COM ::CALC.COM
mdir -i calc.img ::
```

`mdir` must show `CALC.COM`.

## 3. Boot the FreeDOS 1.4 LiveCD

Download and unpack:

```sh
mkdir -p ~/freedos
cd ~/freedos
wget https://download.freedos.org/1.4/FD14-LiveCD.zip
unzip FD14-LiveCD.zip
```

Boot qemu:

```sh
qemu-system-i386 \
  -m 128 \
  -boot d \
  -cdrom ~/freedos/FD14LIVE.iso \
  -drive file=/tmp/calc.img,format=raw,if=floppy \
  -vga std
```

At the FreeDOS menu choose **Use FreeDOS 1.4 in Live Environment mode**.

At the DOS prompt, the LiveCD may take `A:`, so check both drives:

```dos
DIR A:
DIR B:
```

In the tested layout `A:` is the FreeDOS boot floppy and the CALC floppy is
`B:`:

```dos
B:
CALC
```

## 4. Persistent installation

Create a hard-disk image and boot the installer:

```sh
qemu-img create -f raw ~/freedos.img 128M
qemu-system-i386 -m 128 -hda ~/freedos.img \
  -cdrom ~/freedos/FD14LIVE.iso -boot d
```

Install to `C:`, then reboot with both disks attached:

```sh
qemu-system-i386 -m 128 -hda ~/freedos.img \
  -drive file=/tmp/calc.img,format=raw,if=floppy -boot c
```

Inside FreeDOS:

```dos
COPY A:\CALC.COM C:\CALC.COM
C:
CALC
```

## Verified under FreeDOS

Tested under the FreeDOS 1.4 LiveCD in qemu: CALC shows the welcome screen,
starts the spreadsheet, evaluates `1+2` as `3.00`, opens the command menu and
quits through `/Q`.  The same build is expected to work in DOSBox-X because
both use the standard DOS `INT 21h AH=02h` convention: the character is in
`DL`.

That convention was the garbage-screen bug.  The runtime originally put output
characters only in `AL`, because the project's private `bootcom.s` handler read
`AL`; real DOS reads `DL`.  The runtime now sets both, and `bootcom.s` has been
changed to the DOS convention so the harness can no longer hide a future
divergence.

The tested project launcher remains:

```sh
cd shell
python3 tests/calc_cli.py --com CALC.PAS.COM \
  --no-keypress --keys '\r1+2\r/Q'
```