Is it possible to access other hardware from a PCI/USB board/device with realtime OS?

Question

Iron

Hello.
Let's say I plan to make the device in the form of a board connected via PCI or USB. The board will run realtime OS.
Will it be possible to access other computer hardware? (processor, hard drive, RAM, etc.)
Under the computer can be:
- ATX (Mini-ATX) motherboard for x86 processors
- single-board/SOC for x86 processors, arm

Answer 1

The device can generate interrupts. https://ru.wikipedia.org/wiki/Interrupt
How to respond to these interrupts depends on the device driver. If there is no driver, then perhaps there will be no reaction. Or there will be some standard "stub" handler.
For PCI, you can use the DMA mechanism https://ru.wikipedia.org/wiki/Direct_access_to_memory
. But in this case, control is also carried out by the CPU. A PCI device cannot access anywhere it wants to. Only with the highest permission of the CPU.

Answer 2

With proper programming, a device hanging on PCI-e can communicate directly with RAM (via DMA) and directly with another device (for example, this is how Ethernet and disk controllers can communicate) on the same bus.

Answer 3

Of course, if you write a driver for the final OS.

Answer 4

$categories = array('2', '3');
$where = 'WHERE category regexp "(' . implode('|', $categories) . ')"';

Answer 5

Whoever created this table is cancer. Categories are written differently. For example in separate columns. For example in separate bits. For example flags.
In your case, of course, you can do something like
selec t * from table where category ~ '%2% or category ~ '%3%'
but this is cancer.

Answer 6

It's better to remake the database structure, otherwise it's kapets :|