On 01/14/2015 02:07 PM, Carlos E. R. wrote:
On 01/14/2015 09:48 AM, Yamaban wrote:
RS232 was original defined as polling with hardware buffers only. During the later days of the ISA bus (ISA 32bit IIRC) there where cards available the generated a IRQ if new data arrived at the buffers. That was the case with DOS, which had very poor com port support. The operating system itself was very basic, true. But applications commonly supported themselves whatever they needed that the OS did not,
On 2015-01-14 17:40, James Knott wrote: like printer driver, graphic drivers, sound, etc. Interrupt hardware was handled the same way, by the application, or by a TSR. I wrote one myself, using sample code that came with Turbo Pascal from Borland, so it was not that difficult.
Again, that is the software, not hardware that's not using IRQs. The hardware has supported IRQs from the beginning on the IBM PC, as well as long before then on other computers. I mentioned my 8 port serial board that I designed and built for my IMSAI 8080. I built the board to use interrupts and wrote the software to do so as well. So, when the UART needed service, it sent an interrupt, which my software then handled. BTW, in developing & testing that board, I discovered a bug in the Natioal Semiconductor 8250 UART. If the chip was selected, a character send and the chip not deselected, the UART would keep repeating the same character. I had to modify my board logic to work around that. I wrote a letter to National describing the problem. They wrote back to let me know they verified what I said and they hadn't known about that bug prior to my letter.
(By the way, SUSE is cousin to Borland, in a way. Same owner ;-) )
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