serial_find_irq causing issues on 8088-based Tandy 1000 systems

[cml37]

First of all, this code is AMAZING. I was able to easily take it and use it with both Borland and Open Watcom compilers and it works great.

One issue I have noticed is that calling serial_find_irq on my Tandy 1000 SX (as well as a PCem emulated Tandy) causes lockup. My 1000 SX also has a 286 upgrade in it, and when running in 286 mode, it works just fine!

I'll see if I can troubleshoot and post the solution, but wanted to note this in case anyone else picks up this code.

I did try the code on other 8088 emulated systems, and it works just fine, so thinking it is a Tandy issue.

[cml37]

Ah, looks like attempts that work with PIC_SLAVE cause the issues. I did find this little gem: in an online search:

   ; In theory, it should be "safe" to disable NMI in all platforms (PC, PCjr,
   ; and Tandy 1000). But on the Tandy, the first 3 bits of 0xa0 are used to
   ; configure the memory and changing them might crash the computer if not
   ; used correctly.

[cml37]

I worked around this by first detecting whether or not we are using a Tandy, and then whether or not it is an 8088/8086 Tandy. I think that will be sufficient, but this is not widely tested. You can see the work I did here to support that: https://github.com/cml37/DosNabuAdapter/tree/main/src

Only tested in Open Watcom, I did not test with other compilers!