Debugging

[muta...@gmail.com]

I arrived here in the Philippines in the middle of May.

When I was eventually in a position to post here,
I wasn't able to find the trick - since I am using an
Android phone I need to open Google groups as a desktop site,
otherwise "new message" is not available.

I traveled light to the Philippines. I figured I would just buy anything I needed when I got here.

I took a 1.5 tb hard disk with my life on it.
I bought my first smartphone a few months before I left. An Android for US$55 or something. Running Bochs with pdos and freedos and a bit of data. And 3 USB sticks containing pdos, freedos and uc8086.

Very soon after I got here I was reunited with an old laptop.
It had windows and a virus on it 5 years ago,
but had been used for remote pdos testing since then.

When I got it, it had degraded further- only windows recovery mode command prompt worked.

However, all my USB sticks worked, but not together.

I hadn't got very far when I fell down stairs and fractured my ankle.

The pc doesn't have a working battery but does
have a com port.

I couldn't use it because I couldn't easily
get to an electrical outlet, and I preferred to stay
with the air conditioner too.

When I got closer to my destination I briefly had access to another windows laptop.

Otherwise I only had windows recovery mode allowing me to run diskpart and hexdump
and copy files.

Then sometime later even windows recovery mode failed to boot, but I hadn't been using it anyway.

So for the first time ever I was able to install pdos onto a real hard disk.
About 70 GB. The pc is from circa 2011 I think.

It is my nature to freeze and reevaluate
dependencies on software.

I have lost access to git, but not my websits, using my Android.

I have started pdnet but only have messages from people who come to our house.

I have ordered lots of cheap android phones on the
internet. One 4 GB phone costing US$15 delivered is the cheapest.
Every phone was able to run pdos, but
some required an older Bochs.

Originally I used a USB stick to transfer data from the laptop to the android and back. I had a
practical use for pdos-generic after an
enhancement as it allowed me to manipulate
a vhd, not requiring copyrighted mtools.

But I eventually obtained a dodgy android phone that allowed USB mass storage, exposing an SD card, if available, as a normal hard disk,
or internal user memory as a hard disk
without an mbr. Pdos was enhanced
to allow that. Freedos can't.

I can boot my laptop from this android phone
that cost maybe US$20.

1300 pesos it was.

More importantly, I can write data to the android, from pdos or maybe freedos, and then not have to
disconnect anything physically, and send the data via Bluetooth, using the android.

So far I have resisted buying a new laptop, accessing my hard disk, or attempting to get
either windows or Linux working.

That's the background.

I have previously said that I am interested in a "monitor" so that I could debug at an
assembler level. Which is still true.

But that would be in a production environment.

I haven't reached that yet.

I'm still in development where I can add printf.

I was debugging a problem using printf, and reached the limit of what I could do with a single screen, and
solved the problem by adding a fgets from stdin to pause.

But it was time to bite the bullet and have com port debugging.

But I'm going to be screwed if I have a pc without a com port.

I was thinking of using the 1 MB to 2 mb region as a console output buffer that could be scrolled.

But finally I thought of a solution.

My pc only supports the hard disk, 1 USB key and 1 USB HDD.

It took a long time to figure that out.

Luckily pdos86 was on an old 512 mb USB stick that presents as a key.

I can't easily buy new keys, but I found a dodgy place that might work.

Anyway, if I develop on the real hard disk, burn a debug pdos to the USB key, the USB HDD
could then be used as raw storage for console
output. A NUL would indicate EOF.

Pdos could be enhanced to recognize dbg82 as a special device and I could read it using microemacs.

I'll have another special device, maybe dsk8x,
for accessing a raw hard disk as a file for burning images.

I would skip lba 0 for the debug file.

It is odd that Bochs and qemu don't seem to have an option to capture bios screen writes to a file.

Hercules can.

Bochs instead requires intrusive code to write to e9.

Not useful to me at the moment anyway.

Paul.

[muta...@gmail.com]

I am doing a running commentary with screenshots here:

https://discord.gg/Bc6HuWmgHf