I have an android based embedded system, and I would like to command ir controlled devices, such as tv, air conditioner, sound system...etc. I need both rx and tx.
When I see examples on internet, most of them use lirc over gpio.
However, when I see most mobile phones with IR function, they use an IR encoder-decoder IC with an IR transceiver.
Why don't smartphones use gpio directly to control IR ?
"IrDA" is a somewhat more rigidly defined standard than "RC", including: (a) IR intensity / sensitivity vs. distance & speed (b) limiting IR pulses to a maximum length (regardless of what the device driving the IRED might try to do, deliberately or inadvertently) & (c) a 3/16ths encoding scheme, which an intermediary 'Endec' chip (e.g. MCP2120) or an endec module within a UART within a microcontroller (e.g. MSP430F5510) will do for you.
This is most easily achieved with an 'all in 1' module (without the endec) like this, for example:
http://rohmfs.rohm.com/en/products/databook/datasheet/opto/irda_module/rpm841-h16.pdf
Meeting all these specs in bit-banged GPIO when your CPU likely has better things to do is painful. Using a UART, optionally an intermediary Endec chip, and an integrated IrDA module makes implementation much easier. "RC" is different, less stringent.
I think the reason is, that a specific hardware is always faster or even more reliable than the piece of software replacing the hardware. A nice example is the RAID system in computers. Two hard drives can be used as a RAID system when they are controlled by a RAID software. However, a real hardware RAID controller is much faster and therefore better, but more expensive.
Thank you everyone for their answers. My CPU is a 1.2Ghz dual core SoC. When I try ON-OFF toggling a GPIO with an infinite loop in C program, and looking at the result in oscilloscope, I can't get faster than 100uS... May be it need a kernel module to make it faster. It seems this is one of the reasons that manufacturers use a specific hardware for this purpose ?
