NOTE: This option will have no effect with kernel 2.1.131 or later since the irq is handled by the parport driver. You can change the parport irq for example via /proc/parport/*/irq. Read /usr/src/linux/Documentation/parport.txt for more details on parport.
Setting -t <TIME> to 0 is equivalent to setting -c <CHARS> to infinity.
NOTE: This option is obsolete because it's the default in 2.1.131 kernel or later.
This option tells the lp driver to trust or not the IRQ. This option makes sense only if you are using interrupts. If you tell the lp driver to trust the irq, then, when the lp driver will get an irq, it will send the next pending character to the printer unconditionally, even if the printer still claims to be BUSY. This is the only way to sleep on interrupt (and so the handle the irq printing efficiently) at least on Epson Stylus Color Printers. The lp driver automagically detects if you could get improved performance by setting this flag, and in such case it will warn you with a kernel message.
NOTE: Trusting the irq is reported to corrupt the printing on some hardware, you must try to know if your printer will work or not...
-C requires a Linux version prior to 2.1.131.
-T requires a Linux version of 2.1.131 or later.