On Fri, 6 Sep 2013 14:40:14 +0100 Peter Maydell <peter.mayd...@linaro.org> wrote:
> On 6 September 2013 14:00, Antony Pavlov <antonynpav...@gmail.com> wrote: > > On Fri, 6 Sep 2013 08:25:20 +0100 > > Peter Maydell <peter.mayd...@linaro.org> 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
