VT340 Emulation

[Paul Koning]

> On Jun 26, 2021, at 7:08 PM, Maciej W. Rozycki <macro at orcam.me.uk> wrote:
> 
> On Fri, 25 Jun 2021, Paul Koning via cctalk wrote:
> 
>>> Well you can find mother boards with real COM port, but they are rare.
>> 
>> One place you can find them easily is on industrial computers.  My 
>> firewall machine is one, because I wanted it to be fanless.  It has the 
>> usual pile of USB ports and HDMI, but also 2 COM ports; another model of 
>> that same line has 6 COM ports.
>> 
>> What seems to be harder to find is a parallel printer port, but there is 
>> far less reason to want one of those.
> 
> However both serial and parallel ports remain reasonably available as 
> PCIe option devices.  Though parallel ports seem to be made as legacy PCIe 
> devices only, that is accessed with I/O rather than memory read/write bus 
> cycles, which are not, as I have learnt the hard way recently, supported 
> by all computer systems nowadays.  I guess x86 systems will continue to 
> support them however as x86 CPUs have native I/O access instructions.

I/O cycles on PCI have no direct connection to I/O instructions.  I've routinely used I/O operations in PCI on a MIPS platform, which of course has no such concept; all that was needed is to send the memory cycles to the address block that the PCI bridge maps onto I/O cycles rather than memory cycles.

	paul