How to know if an IRQ value is free to use

If we add a device that does not support PNP (Plug-an Play), the manufacturer will hopefully provide explicit directions on how to assign IRQ values for it. However, if we don't know what IRQ value to specify, what command line should be used to check if a IRQ value is free or not? lsdev displays info about devices: $lsdev Device DMA IRQ I/O Ports ------------------------------------------------ 0000:00:02.0 7000-703f 0000:00:1f.2 7060-707f 7080-7087 7088-708f 7090-7093 7094-7097 0000:00:1f.3 efa0-efbf 0000:01:00.0 6000-607f 0000:04:00.0 4000-40ff 0000:05:00.0 3000-30ff acpi 9 ACPI 1800-1803 1804-1805 1808-180b 1810-1815 1820-182f 1850-1850 ahci 43 7060-707f 7080-7087 7088-708f 7090-7093 7094-7097 cascade 4 What about this cmd lsdev, is it enough for this task? For example, if we want to know if 1233 is free, we would run this command: lsdev | awk '{print $3}'|grep 1233 **NOTE:** $3 above is used because IRQ value printed in the 3rd column of lsdev output. Then if no output, it means that it is free for us to use?