native: add UART driver based on /dev/tty

[Yonezawa-T2]

uart0 functionality is removed by #3164. This PR implements periph/uart, rather than deprecated uart0, using /dev/tty. A TTY device is specified on command line with -c (COM) option, since -t was used by the old implementation.

To use with netdev2_tap simultaneously, this PR adds asynchronus read system and modifies netdev2_tap to use it. It monitors multiple file descriptors by fcntl O_ASYNC option on non OS X system and by select system call on OS X system. It forks child process on OS X system.

I'm struggling to make my Mac with XBee connected by USB to be a border router of 6LoWPAN and made several fixes. Other fixes will be filled as separate pull requests. This PR also implements empty GPIO driver needed by the xbee driver.

Tested on OS X.

[OlegHahm]

Very nice PR - this feature is very much missing for a long time.

[kaspar030]

Yep. @Yonezawa-T2 Thanks for getting into this!

[Yonezawa-T2]

We have to update the wiki page when this PR is merged.

[Yonezawa-T2]

I met a problem with netdev2_tap. It deadlocks when there are no spaces in pktbuf (for example, when packets are arriving too quickly).

For OS X, the child process monitoring file descriptors are suspended until explicitly resumed by the _recv function of netdev2_tap. When gnrc_netdev2_eth failed to allocate pktbuf, it does not call _recv function of netdev2_tap.

Possible solutions:

• A) notifying error from gnrc_netdev2_eth to netdev2_tap to cleanup things
• B) timeouting the suspension in async_read.c
• C) checking memory availability in netdev2_tap

A)
Pros: cleanest way to do it
Cons: adds extra API for netdev2 driver

B)
Pros: no API changes
Pros: robust
Cons: OS X does not have sigtimedwait
Cons: suspends until timeout

C)
Pros: no API changes
Pros: resumes quickly
Cons: checking memory availability may be costly
Cons: relying on internal of gnrc_netdev2_eth (i.e. how much memory it requires)
Reference implementation: Yonezawa-T2@5a750a4

Which is better? Any alternatives?

[miri64]

Reassigned to @kaspar030 since he is Mr. netdev2_eth ;)

[kaspar030]

A) notifying error from |gnrc_netdev2_eth| to |netdev2_tap| to cleanup things

So what needs to happen is that if gnrc_netdev2_eth cannot allocate the pktbuf, it needs to somehow flush the current packet from netdev2_tap. right? We could piggyback that into recv(). Currently, if recv() is called with a NULL pointer as buffer, it will just return the length of the packet. We could make it drop the packet if buffer is NULL but length equals expected packet length, or something like that. Another option would be a set() call that flushes one (or all) packets.

[kaspar030]

C) doesn't seem like a good option as it messes with the layering (netdev2 itself was designed to be independent of gnrc, so we can't call any gnrc_* stuff there).

[kaspar030]

B) seems tap specific.

[Yonezawa-T2]

Implemented A.

[Yonezawa-T2]

Rebased and resolved conflict with #3984.

[OlegHahm]

Can you tell me how this is supposed to work? Where should uart_init()be called?

[Yonezawa-T2]

@OlegHahm For example, when using XBee, uart_init is called from xbee_init:

• auto_init
• → auto_init_xbee (if xbee module is enabled)
• → xbee_init
• → uart_init

uart_init opens a TTY device file and registers a callback function, which is called from interrupt handler for SIGIO.

TTY devices are specified by command-line option -c, that are handled by cpu/native/startup.c, registered by tty_uart_setup. Multiple devices are allowed by repeating -c option. uart_init must be called after TTY devices are registered.

SIGIO is shared with netdev2_tap using new async_read.c, which uses select to detect which file descriptor is readable and which callback function should be invoked.

[Yonezawa-T2]

rebased

[Yonezawa-T2]

Rebased and updated GPIO function signatures.

[OlegHahm]

@kYc0o, @emmanuelsearch, @thomaseichinger, can you test?

[kYc0o]

Yes we can!

[kYc0o]

I'm having this on native with Apple LLVM version 7.3.0 (clang-703.0.29):

Building application "periph_uart" for "native" with MCU "native".

/Users/facosta/git/RIOT2/RIOT/tests/periph_uart/main.c:59:24: error: comparison of integers of different signs: 'int' and 'unsigned int' [-Werror,-Wsign-compare]
    if (dev < 0 || dev >= UART_NUMOF) {
                   ~~~ ^  ~~~~~~~~~~
/Users/facosta/git/RIOT2/RIOT/tests/periph_uart/main.c:182:23: error: comparison of integers of different signs: 'int' and 'unsigned int' [-Werror,-Wsign-compare]
    for (int i = 0; i < UART_NUMOF; i++) {

[Yonezawa-T2]

Fixed and rebased.

[kYc0o]

Tested and working correctly, waiting for Murdock

[Yonezawa-T2]

Created #5198 and #5199 for Murdock errors.

[OlegHahm]

Both are merged. Please rebase.

[Yonezawa-T2]

Rebased.

[OlegHahm]

Let's try to merge this before Sunday (another exception from the feature freeze).

[Yonezawa-T2]

Murdock passed (except NEEDS SQUASHING static-test). Squashed.

[kYc0o]

Murdock happy -> GO!

[Yonezawa-T2]

Updated the wiki pages.
https://github.com/RIOT-OS/RIOT/wiki/Family:-native
https://github.com/RIOT-OS/RIOT/wiki/Board%3A-native

[OlegHahm]

Cool - many thanks!