[U-Boot-Users] How To Register Interrupt Routines in ARM920T?

Wolfgang Denk wd at denx.de
Wed Dec 8 10:10:55 CET 2004

In message <698a2fda0412072241b442444 at mail.gmail.com> you wrote:
> I am porting U-Boot to a custom board (ARM920T) and I have to do
> something about the UART (ns16550.c) driver to support (I know WD
> would disagree with this :p) XON/XOFF.  I have to do this because my

There are certain situations  where  you  actually  may  have  to  do
something like this, like when your serial connectionis over modem or

> board can support only < 19200 baudrates.  At 19200 baudrate, I have a

This is NOT a valid reson. We use many boards at  9600  bps,  without
any flow control. The baud rate has NOTHING to do with this.

> functional serial console but downloading binaries using loadb, kermit
> would always say that the remote host is not reponding (ERROR: Remote
> Kermit Not Responding).  I debugged this on the getc level and
> verified that my board's U-Boot can accept the first few data from my
> PC's kermit and then the loadb function hangs, i.e. does not accept
> any data.  I think this is because my UART's FIFO is not handled well,
> and probably needs software flow control.

You are wrong. This has NOTHING to do with flow  control.  Even  slow
systems are fast enought to pick up characters loss-free at high baud
rates  like  115200 bps - remember that we are single tasking, so the
CPU really has nothing more to do than wait for the characters. So  a
_slow_  connection  is only _easier_ to handle. If you have problems,
these have other reasons (like a misconfigured kermit ?).

> How do I register my interrupt routine that would send XOFF data to

You don't.

First, you're wrong when you think that flow  control  would  improve
this problem.

Second, you are wrong when you think you need interrupts to implement
flow control.

Don't waste your time, you're on a wrong track.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
"Faith: not *wanting* to know what is true."    - Friedrich Nietzsche

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