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Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support
From: |
Antony Pavlov |
Subject: |
Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support |
Date: |
Sat, 7 Sep 2013 09:45:13 +0400 |
On Fri, 6 Sep 2013 14:40:14 +0100
Peter Maydell <address@hidden> wrote:
> 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 don't want publish Canon firmware disassembled listings and discuss it
in the maillist for legal reasons.
But Canon A1100 firmware can use this routine:
1. wait TX_RDY bit in status register;
2. write TX_RDY and some other (unknown behaviour) bit to status register;
3. write byte to TX register.
IMHO the step 2 is bizarre.
You can easely check me: the disassembly instructions and firmware images can
be found via CHDK site. A puts()-like routine can be found at 0xffff18f0
in the Canon A1100IS firmware image.
> 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
IMHO the more standart UART outc() routune is:
* wait for UART "transmitter is ready to send next char" flag;
* write char to TX register.
E.g. see
https://github.com/frantony/barebox/blob/master/arch/mips/include/asm/debug_ll_ns16550.h#L60
or
https://github.com/frantony/barebox/blob/master/arch/arm/mach-imx/include/mach/debug_ll.h#L49
--
Best regards,
Antony Pavlov
- Re: [Qemu-devel] [RFC v4 1/5] hw/arm: add very initial support for Canon DIGIC SoC, (continued)
[Qemu-devel] [RFC v4 3/5] hw/arm/digic: add timer support, Antony Pavlov, 2013/09/05
[Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Antony Pavlov, 2013/09/05
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Peter Maydell, 2013/09/05
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Antony Pavlov, 2013/09/06
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Peter Maydell, 2013/09/06
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Antony Pavlov, 2013/09/06
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Peter Maydell, 2013/09/06
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support,
Antony Pavlov <=
- Re: [Qemu-devel] [RFC v4 4/5] hw/arm/digic: add UART support, Peter Maydell, 2013/09/07
[Qemu-devel] [RFC v4 2/5] hw/arm/digic: prepare DIGIC-based boards support, Antony Pavlov, 2013/09/05
[Qemu-devel] [RFC v4 5/5] hw/arm/digic: add NOR ROM support, Antony Pavlov, 2013/09/05