[En-Nut-Discussion] RFC: spibus: Return status of MISO line with transfer with xlen == 0;

[Uwe Bonnes]

Hello,

e.g. the LTC24xx delta-sigma converters with spi connection provide a static
value on MISO to indicate conversion completion. With the present owibus
driver, I don't see a way to query MISO via the driver. Instead the IO pin
has to be queried by GPIO commands, requiring the user program  to know the
MISO line.

I have a patch, extending the spi bus transfer functionality like:

/*!
  * \brief Transfer data on the SPI bus using single buffered interrupt mode.
  *
  * A device must have been selected by calling At91SpiSelect().
  *
+ * With xlen = 0, the status of the MISO line is returned.
+ *
  * \param node  Specifies the SPI bus node.
  * \param txbuf Pointer to the transmit buffer. If NULL, undetermined
  *              byte values are transmitted.
  * \param rxbuf Pointer to the receive buffer. If NULL, then incoming
  *              data is discarded.
  * \param xlen  Number of bytes to transfer.
  *
- * \return Always 0.
+ * \return Status of Miso with xlen == 0, 0 else.
  */

Use like:
        rc = (*bus->bus_transfer) (node, NULL, NULL, 0);

and implemented in following file:

 nut/arch/avr/dev/spibus0avr.c           |  7 ++++++-
 nut/arch/cm3/dev/nxp/lpc176x_spi.c      |  7 ++++++-
 nut/arch/cm3/dev/stm/stm32_spi.c        |  9 ++++++---
 nut/dev/spibus0gpio.c                   | 13 ++++++++++++-
 nut/dev/spibus_npl.c                    |  2 ++
 9 files changed, 42 insertions(+), 6 deletions(-)

Only a fixme is added for some archs where I don't understand GPIO handling:
 nut/arch/arm/dev/atmel/spibus0at91.c    |  2 ++
 nut/arch/arm/dev/atmel/spibus0at91ssc.c |  2 ++
 nut/arch/arm/dev/atmel/spibus1at91.c    |  2 ++
 nut/arch/arm/dev/atmel/spibus_at91.c    |  4 ++++
but not for some other archs.

Question:
- Does this approach make sense?
- Is it right to apply the patch even when for some archs the feature is not
 implemented?

Cheers
-- 
Uwe Bonnes                bon at elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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