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Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support

From: Peter Maydell
Subject: Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support
Date: Fri, 6 Sep 2013 14:40:14 +0100

On 6 September 2013 14:00, Antony Pavlov <address@hidden> wrote:
> On Fri, 6 Sep 2013 08:25:20 +0100
> Peter Maydell <address@hidden> wrote:
>> You can deduce its existence though -- does the
>> UART let you feed two or three characters to it
>> at faster than whatever the serial line speed is
>> before it sets the "stop sending me bits" status
>> bit, or does it stop after the first?
> No, I can't :)
> How can I check this mysterious "stop sending me bits" status bit?
> Do you mean the UART hardware flow control pin?

I meant ST_TX_RDY, but looking again at the
docs perhaps I misinterpreted it. Do you really
have to do:
 * write byte to TX register
 * set TX_RDY bit in status register

to get it to send out a byte?

I was expecting a more standard UART interface
which is typically:
 * write byte to TX register
 * if the UART is unable to accept any more
   bytes (ie FIFO full, or just immediately if
   no FIFO present) it clears TX_RDY
 * software has to wait for TX_RDY to be set
   before writing another byte to TX

-- PMM

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