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I’m trying to write to my lpt register with the function outb(0x378,val);
well.. I tried to debug with the call int ret=inb(0x378); I always get the ret=255 no matter what value I insert with outb before.
*I’m writing on the kernel mode since my program is a driver, therefore I didn’t use ioperm() etc.
thank you in advance.
Do you know for a fact that you have a parallel port installed at that address?
Get yourself a small low-current LED. Stick the long end in one of pin 2 (LSB) to pin 9 (MSB) and the short end in pin 25 (ground).
Try writing various values and see if you can get the LED to change by the bit value of what you write.
This should work (unless as previously mentioned you’ve gotten it programmed in an input mode) Being able to read back the port value is less certain, depending on the type of parallel port and implementation details (for example, you probably couldn’t with the buffer chip that implemented it in the original PC)
Also note that most USB “printer” adapters don’t give you bitwise register access. Something hanging off of the PCI or PCMCIA, etc may also have problems with direct register access at the legacy port address. There are nice USB parallel interface chips such as the FT245 and successors which you can use if you don’t have a “true” parallel port hanging off the chipset available.