Michael Schnell wrote:
On 07/03/2013 06:36 PM, Dennis Poon wrote:
Can you give me some pointer on directly using UART? I need to
implement half-duplex using UART for rs-485 protocol.
In a Linux system, accessing the hardware by user code is strictly
discouraged, at least whenever interrupts are involved (as with
UARTs). A decent system should provide rs-485 support in the "TTY"
driver, when the hardware allows for such.
If your system does not do so, you should find or do a device driver
yourself.
In fact what do you mean by "rs-485 protocol" ?
With RS-485 hardware you can - and supposedly need to - do
"half-duplex with output enable", if your hardware provides this.
After days of google search, I am afraid the bcm2835, the Soc of
Raspberry Pi (the hardware I have to use) does not provide this hardware
support :-(
It states that it does not even support interrupt. Polling is the only
way for events :-(
The hardware might or might not provide automatic output enable (if
not, you need to set and reset RTS in software).
The hardware might or might not provide echo cancellation (if not the
software needs to actively ignore anything that the hardware echoes
back when sending it).
If your hardware provides both auto output enable and echo
cancellation, your software can happily ignore the "rs-485 protocol".
Usually both can be done in userland software even with standard TTY
drivers that (usually do) setting and resetting support RTS, or
(better) by dedicated support in the device driver.
I have no experience in the above tasks you mentioned :-( It's going to
take many days of trial and error. haiiii......
Thanks for your advice.
Dennis
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