Extend the RTC framework with an alarm read ioctl (RTC_RD_ALARM). Through it consumer could get configuration settings about previously scheduled hardware alarms (active status, hours, minutes, seconds).

Master

* stm32_dac.c: fix compilation when DMA disabled for channel

* smps.h: update some comments

* smps.c: more sanity checks

Approved-by: Gregory Nutt <gnutt@nuttx.org>

networking:  IGMP: Remove special support for interrupt level processing (there is none) and fix some timer cancellation logic.  In many files, correct comments.  There is no interrupt level processing in the networking layer.

stm32f7: do not enable read-modify-write on DTCM.  "AN 4667 - STM32F7 Series system architecture and performance" recommends to disable read-modify-write on DTCM: "If the DTCM-RAM is used as data location and the variables used are byte or/and halfword types, since there is no ECC management in this RAM on the STM32F7 Series, it is recommended to disable the read-modify-write of the DTCM-RAM in the DTCM interface (inthe DTCMCR register) to increase the performance."

Some STM32L4 DAC changes

Approved-by: Gregory Nutt <gnutt@nuttx.org>

net_timedwait() and net_lockedwait() no longer return errors via errno but returned negated errno values like other internal OS functions.

Signed-off-by: Juha Niskanen <juha.niskanen@haltian.com>

User should not be bothered by details like how many IP blocks there are. As no
current STM32L4 has second DAC block (channel 3), remove support for such
hypothetical hardware. DMA channels corrected.

Change-Id: I2cba7e55803871f1ff945538113f12cf5088f68d
Signed-off-by: Juha Niskanen <juha.niskanen@haltian.com>

Change-Id: Ibc6dc90b39b784b5534b8908eaf615bf1ddcb7ed
Signed-off-by: Juha Niskanen <juha.niskanen@haltian.com>

Actually write something to the DAC DMA buffer.

Change-Id: I1b2516ac26fb17f5242611b56be8926c5f40c2c7
Signed-off-by: Juha Niskanen <juha.niskanen@haltian.com>

This reverts commit ad2ef95d.

stm32 FLASH allow non blocking operation on constrained devices

Approved-by: Gregory Nutt <gnutt@nuttx.org>

   On a very memory constrained device with a single task. The
   sem_wait and sem_post operations can be disabled, to save space.
   The default is blocking enabled.

I'm worried about the stm32_tim_getcounter funtion. It returns always 32 bits. But major stm32 timers have 16 bits counters. I think, it's not a good idea to return the memory behind the TIMx_CNT register.  This changes adds the register size checking.

Work queue:  In a recent change for a problem noted by Pascal Speck, it was noted (again by Pascal Speck) that the cancellation of existing work and replacement with new work must be atomic.  Thanks, Pascal.

Networking:  Fix a race condition.  The accept() operation is performed with the network locked.  However, the network is unlocked BEFORE the connected state is set.  Therefore, a context switch may occur and the socket may no longer be connected when it is marked so.  Noted by Pascal Speck.

ARM syscall logic:  Clear bit 0 in PC settings.  Bit 0 is the thumb mode indication and should not be set in the PC.

Mostly cosmetic changes from review of last PR.  Also same inappropriate use of _info changes to configurable debug macros.  Remember folks, if it has a _ or __ in front, it is not intended for use outside of the header file.  It is an internal private definition.