paulkoning at comcast.net
Sun Jun 27 09:29:52 CDT 2021
> 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.
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