This new element takes the form: (ELEM_TYPE_STATUS, 4, <address>). If this
element is present in the mboot command then mboot will store to the given
address the result of the filesystem firmware update process. The address
can for example be an RTC backup register.
Signed-off-by: Damien George <damien@micropython.org>
Instead it is now passed in as an optional parameter to the ELEM_MOUNT
element, with a compile-time configurable default.
Signed-off-by: Damien George <damien@micropython.org>
The superblock for littlefs is in block 0 and 1, but block 0 may be erased
or partially written, so block 1 must be checked if block 0 does not have a
valid littlefs superblock in it.
Prior to this commit, if block 0 did not contain a valid littlefs
superblock (but block 1 did) then the auto-detection would fail, mounting a
FAT filesystem would also fail, and the system would reformat the flash,
even though it may have contained a valid littlefs filesystem. This is now
fixed.
Signed-off-by: Damien George <damien@micropython.org>
To match the definition of GENERATE_PACK_DFU, so a board can customise the
location/name of this file if needed.
Signed-off-by: Damien George <damien@micropython.org>
To have at least one board configured with MBOOT_ENABLE_PACKING, for CI
testing purposes and demonstration of the feature.
Signed-off-by: Damien George <damien@micropython.org>
This commit adds support to stm32's mboot for signe, encrypted and
compressed DFU updates. It is based on inital work done by Andrew Leech.
The feature is enabled by setting MBOOT_ENABLE_PACKING to 1 in the board's
mpconfigboard.mk file, and by providing a header file in the board folder
(usually called mboot_keys.h) with a set of signing and encryption keys
(which can be generated by mboot_pack_dfu.py). The signing and encryption
is provided by libhydrogen. Compression is provided by uzlib. Enabling
packing costs about 3k of flash.
The included mboot_pack_dfu.py script converts a .dfu file to a .pack.dfu
file which can be subsequently deployed to a board with mboot in packing
mode. This .pack.dfu file is created as follows:
- the firmware from the original .dfu is split into chunks (so the
decryption can fit in RAM)
- each chunk is compressed, encrypted, a header added, then signed
- a special final chunk is added with a signature of the entire firmware
- all chunks are concatenated to make the final .pack.dfu file
The .pack.dfu file can be deployed over USB or from the internal filesystem
on the device (if MBOOT_FSLOAD is enabled).
See #5267 and #5309 for additional discussion.
Signed-off-by: Damien George <damien@micropython.org>
Prior to this fix, the final piece of data in a compressed file may have
been lost when decompressing.
Signed-off-by: Damien George <damien@micropython.org>
Mboot builds do not use the external SPI flash in caching mode, and
explicitly disabling it saves RAM and a small bit of flash.
Signed-off-by: Damien George <damien@micropython.org>
This only needs to be enabled if a board uses FAT FS on external SPI flash.
When disabled (and using external SPI flash) 4k of RAM can be saved.
Signed-off-by: Damien George <damien@micropython.org>
When littlefs is enabled extended reading must be supported, and using this
function to read the first block for auto-detection is more efficient (a
smaller read) and does not require a cached SPI-flash read.
Signed-off-by: Damien George <damien@micropython.org>
These functions enable SDRAM data retention in stop mode. Example usage,
in mpconfigboard.h:
#define MICROPY_BOARD_ENTER_STOP sdram_enter_low_power();
#define MICROPY_BOARD_LEAVE_STOP sdram_leave_low_power();
Calculate the bit timing from baudrate if provided, allowing sample point
override. This makes it a lot easier to make CAN work between different
MCUs with different clocks, prescalers etc.
Tested on F4, F7 and H7 Y/V variants.
This much buffer space is required for CDC data out endpoints to avoid any
buffer overflows when the USB CDC is saturated with data.
Signed-off-by: Damien George <damien@micropython.org>
The -Og optimisation level produces a more realistic build, gives a better
debugging experience, and generates smaller code than -O0, allowing debug
builds to fit in flash.
This commit also assigns variables in can.c to prevent warnings when -Og is
used, and builds a board in CI with DEBUG=1 enabled.
Signed-off-by: Damien George <damien@micropython.org>
Allows reserving CAN, I2C, SPI, Timer and UART peripherals. If reserved
the peripheral cannot be accessed from Python.
Signed-off-by: Damien George <damien@micropython.org>
Even though IRQs are disabled this seems to be required on H7 Rev Y,
otherwise Systick interrupt triggers and the MCU leaves the stop mode
immediately.
This commit saves OSCs/PLLs state before STOP mode and restores them on
exit. Some boards use HSI48 for USB for example, others have PLL2/3
enabled, etc.
Also known as L2CAP "connection oriented channels". This provides a
socket-like data transfer mechanism for BLE.
Currently only implemented for NimBLE on STM32 / Unix.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
Hardware I2C implementations must provide a .init() protocol method if they
want to support reconfiguration. Otherwise the default is that i2c.init()
raises an OSError (currently the case for all ports).
mp_machine_soft_i2c_locals_dict is renamed to mp_machine_i2c_locals_dict to
match the generic SPI bindings.
Fixes issue #6623 (where calling .init() on a HW I2C would crash).
Signed-off-by: Damien George <damien@micropython.org>
This fixes the build for non-STM32WB based boards when the NimBLE submodule
has not been fetched, and also allows STM32WB boards to build with BLE
disabled.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This is needed to moderate concurrent access to the internal flash, as
while an erase/write is in progress execution will stall on the wireless
core due to the bus being locked.
This implements Figure 10 from AN5289 Rev 3.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This commit switches the STM32WB HCI interface (between the two CPUs) to
require the use of MICROPY_PY_BLUETOOTH_USE_SYNC_EVENTS, and as a
consequence to require NimBLE. IPCC RX IRQs now schedule the NimBLE
handler to run via mp_sched_schedule.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This changes stm32 from using PENDSV to run NimBLE to use the MicroPython
scheduler instead. This allows Python BLE callbacks to be invoked directly
(and therefore synchronously) rather than via the ringbuffer.
The NimBLE UART HCI and event processing now happens in a scheduled task
every 128ms. When RX IRQ idle events arrive, it will also schedule this
task to improve latency.
There is a similar change for the unix port where the background thread now
queues the scheduled task.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This requires that the event handlers are called from non-interrupt context
(i.e. the MicroPython scheduler).
This will allow the BLE stack (e.g. NimBLE) to run from the scheduler
rather than an IRQ like PENDSV, and therefore be able to invoke Python
callbacks directly/synchronously. This allows writing Python BLE handlers
for events that require immediate response such as _IRQ_READ_REQUEST (which
was previous a hard IRQ) and future events relating to pairing/bonding.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
Devices with RTC backup-batteries have been shown (very rarely) to have
incorrect RTC prescaler values. Such incorrect values mean the RTC counts
fast or slow, and will be wrong forever if the power/backup-battery is
always present.
This commit detects such a state at start up (hard reset) and corrects it
by reconfiguring the RTC prescaler values.
Signed-off-by: Damien George <damien@micropython.org>
And rename SRC_HAL -> HAL_SRC_C and SRC_USBDEV -> USBDEV_SRC_C for
consistency with other source variables.
Follow on from 0fff2e03fe
Signed-off-by: Damien George <damien@micropython.org>
The file `$(BUILD)/firmware.bin` was used by the target `deploy-stlink` and
`deploy-openocd` but it was generated indirectly by the target
`firmware.dfu`.
As this file could be used to program boards directly by a Mass Storage
copy, it's better to make it explicitly generated.
Additionally, some target are refactored to remove redundancy and be more
explicit on dependencies.
Running the update inside the soft-reset loop will mean that (on boards
like PYBD that use a bootloader) the same reset mode is used each
reset loop, eg factory reset occurs each time.
Signed-off-by: Damien George <damien@micropython.org>
The same seed will only occur if the board is the same, the RTC has the
same time (eg freshly powered up) and the first call to this function (eg
via an "import random") is done at exactly the same time since reset.
Signed-off-by: Damien George <damien@micropython.org>
Prior to this commit, the ADC calibration code was never executing because
ADVREGEN bit was set making the CR register always non-zero.
This commit changes the logic so that ADC calibration is always run when
the ADC is disabled and an ADC channel is initialised. It also uses the LL
API functions to do the calibration, to make sure it is done correctly on
each MCU variant.
Signed-off-by: Damien George <damien@micropython.org>
If the device is not connected over USB CDC to a host then all output to
the CDC (eg initial boot messages) is written to the CDC TX buffer with
wrapping, so that the most recent data is retained when the USB CDC is
eventually connected (eg so the REPL banner is displayed upon connection).
This commit fixes a bug in this behaviour, which was likely introduced in
e4fcd216e0, where the initial data in the CDC
TX buffer is repeated multiple times on first connection of the device to
the host.
Signed-off-by: Damien George <damien@micropython.org>
When installing WS firmware, the very first GET_STATE can take several
seconds to respond (especially with the larger binaries like
BLE_stack_full).
Allows stm.rfcore_sys_hci to take an optional timeout, defaulting to
SYS_ACK_TIMEOUT_MS (which is 250ms).
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
The flash can sometimes be in an already-unlocked state, and attempting to
unlock it again will cause an immediate reset. So make _Flash.unlock()
check FLASH_CR_LOCK to get the current state.
Also fix some magic numbers for FLASH_CR_LOCK AND FLASH_CR_STRT.
The machine.reset() could be removed because it no longer crashes now that
the flash unlock is fixed.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
This commit adds a script that can be run on-device to install FUS and WS
binaries from the filesystem. Instructions for use are provided in
the rfcore_firmware.py file.
The commit also removes unneeded functionality from the existing rfcore.py
debug script (and renames it rfcore_debug.py).
The new functions provide FUS/WS status, version and SYS HCI commands:
- stm.rfcore_status()
- stm.rfcore_fw_version(fw_id)
- stm.rfcore_sys_hci(ogf, ocf, cmd)
Changes are:
- Fix missing IRQ handler when SDMMC2 is used instead of SDMMC1 with H7
MCUs.
- Removed outdated H7 series compatibility macros.
- Defined common IRQ handler macro for F4 series.
It requires mp_hal_time_ns() to be provided by a port. This function
allows very accurate absolute timestamps.
Enabled on unix, windows, stm32, esp8266 and esp32.
Signed-off-by: Damien George <damien@micropython.org>
With a warning that this way of constructing software I2C/SPI is
deprecated. The check and warning will be removed in a future release.
This should help existing code to migrate to the new SoftI2C/SoftSPI types.
Signed-off-by: Damien George <damien@micropython.org>
Previous commits removed the ability for one I2C/SPI constructor to
construct both software- or hardware-based peripheral instances. Such
construction is now split to explicit soft and non-soft types.
This commit makes both types available in all ports that previously could
create both software and hardware peripherals: machine.I2C and machine.SPI
construct hardware instances, while machine.SoftI2C and machine.SoftSPI
create software instances.
This is a breaking change for use of software-based I2C and SPI. Code that
constructed I2C/SPI peripherals in the following way will need to be
changed:
machine.I2C(-1, ...) -> machine.SoftI2C(...)
machine.I2C(scl=scl, sda=sda) -> machine.SoftI2C(scl=scl, sda=sda)
machine.SPI(-1, ...) -> machine.SoftSPI(...)
machine.SPI(sck=sck, mosi=mosi, miso=miso)
-> machine.SoftSPI(sck=sck, mosi=mosi, miso=miso)
Code which uses machine.I2C and machine.SPI classes to access hardware
peripherals does not need to change.
Signed-off-by: Damien George <damien@micropython.org>
The SoftSPI constructor is now used soley to create SoftSPI instances, it
can no longer delegate to create a hardware-based SPI instance.
Signed-off-by: Damien George <damien@micropython.org>
The SoftI2C constructor is now used soley to create SoftI2C instances, it
can no longer delegate to create a hardware-based I2C instance.
Signed-off-by: Damien George <damien@micropython.org>
Also rename machine_i2c_type to mp_machine_soft_i2c_type. These changes
make it clear that it's a soft-I2C implementation, and match SoftSPI.
Signed-off-by: Damien George <damien@micropython.org>
The device info table has a different layout when core 2 is in FUS mode.
In particular it's larger than the 32 bytes used when in WS mode and if the
correct amount of space is not allocated then the end of the table may be
overwritten with other data (eg with FUS version 0.5.3). So update the
structure to fix this.
Also update rfcore.py to disable IRQs (which are enabled by rfcore.c), to
not depend on uctypes, and to not require the asm_thumb emitter.
Signed-off-by: Damien George <damien@micropython.org>
For time-based functions that work with absolute time there is the need for
an Epoch, to set the zero-point at which the absolute time starts counting.
Such functions include time.time() and filesystem stat return values. And
different ports may use a different Epoch.
To make it clearer what functions use the Epoch (whatever it may be), and
make the ports more consistent with their use of the Epoch, this commit
renames all Epoch related functions to include the word "epoch" in their
name (and remove references to "2000").
Along with this rename, the following things have changed:
- mp_hal_time_ns() is now specified to return the number of nanoseconds
since the Epoch, rather than since 1970 (but since this is an internal
function it doesn't change anything for the user).
- littlefs timestamps on the esp8266 have been fixed (they were previously
off by 30 years in nanoseconds).
Otherwise, there is no functional change made by this commit.
Signed-off-by: Damien George <damien@micropython.org>
To portably get the Epoch. This is simply aliased to localtime() on ports
that are not timezone aware.
Signed-off-by: Damien George <damien@micropython.org>
This allows prototyping rfcore.c improvements from Python.
This was mostly written by @dpgeorge with small modifications to work after
rfcore_init() by @jimmo.
Before this change there was up to a 128ms delay on incoming payloads from
CPU2 as it was polled by SysTick. Now the RX IRQ immediately schedules the
PendSV.
This is required to allow using WS firmware newer than 1.1.1 concurrently
with USB (e.g. USB VCP). It prevents CPU2 from modifying the CLK48 config
on boot.
Tested on WS=1.8 FUS=1.1.
See AN5289 and https://github.com/micropython/micropython/issues/6316
- Split tables and buffers into SRAM2A/2B.
- Use structs rather than word offsets to access tables.
- Use FLASH_IPCCDBA register value rather than option bytes directly.
Previously the interaction between the different layers of the Bluetooth
stack was different on each port and each stack. This commit defines
common interfaces between them and implements them for cyw43, btstack,
nimble, stm32, unix.
mp_irq_init() is useful when the IRQ object is allocated by the caller.
The mp_irq_methods_t.init method is not used anywhere so has been removed.
Signed-off-by: Damien George <damien@micropython.org>
Updating to Black v20.8b1 there are two changes that affect the code in
this repository:
- If there is a trailing comma in a list (eg [], () or function call) then
that list is now written out with one line per element. So remove such
trailing commas where the list should stay on one line.
- Spaces at the start of """ doc strings are removed.
Signed-off-by: Damien George <damien@micropython.org>
Prior to this commit, if you configure a pin as an output type (I2C in this
example) and then later configure it back as an input, then it will report
the type incorrectly. Example:
>>> import machine
>>> b6 = machine.Pin('B6')
>>> b6
Pin(Pin.cpu.B6, mode=Pin.IN)
>>> machine.I2C(1)
I2C(1, scl=B6, sda=B7, freq=420000)
>>> b6
Pin(Pin.cpu.B6, mode=Pin.ALT_OPEN_DRAIN, pull=Pin.PULL_UP, af=Pin.AF4_I2C1)
>>> b6.init(machine.Pin.IN)
>>> b6
Pin(Pin.cpu.B6, mode=Pin.ALT_OPEN_DRAIN, af=Pin.AF4_I2C1)
With this commit the last print now works:
>>> b6
Pin(Pin.cpu.B6, mode=Pin.IN)
The SCSI driver calls GetCapacity to get the block size and number of
blocks of the underlying block-device/LUN. It caches these values and uses
them later on to verify that reads/writes are within the bounds of the LUN.
But, prior to this commit, there was only one set of cached values for all
LUNs, so the bounds checking for a LUN could use incorrect values, values
from one of the other LUNs that most recently updated the cached values.
This would lead to failed SCSI requests.
This commit fixes this issue by having separate cached values for each LUN.
Signed-off-by: Damien George <damien@micropython.org>
This code is imported from musl, to match existing code in libm_dbl.
The file is also added to the build in stm32/Makefile. It's not needed by
the core code but, similar to c5cc64175b,
allows round() to be used by user C modules or board extensions.
Polling mode will cause failures with the mass-erase command due to USB
timeouts, because the USB IRQs are not being serviced. Swiching from
polling to IRQ mode fixes this because the USB IRQs can be serviced between
page erases.
Note that when the flash is being programmed or erased the MCU is halted
and cannot respond to USB IRQs, because mboot runs from flash, as opposed
to the built-in bootloader which is in system ROM. But the maximum delay
in responding to an IRQ is the time taken to erase a single page, about
100ms for large pages, and that is short enough that the USB does not
timeout on the host side.
Recent tests have shown that in the current mboot code IRQ mode is pretty
much the same speed as polling mode (within timing error), code size is
slightly reduced in IRQ mode, and IRQ mode idles at about half of the power
consumption as polling mode.
This is treated more like a "delay before continuing" in the spec and
official tools and does not appear to be really needed. In particular,
downloading firmware is much slower with non-zero timeouts because the host
must pause by the timeout between sending each DFU_GETSTATUS to poll for
download/erase complete.
The implementation internally uses sector erase to wipe everything except
the sector(s) that mboot lives in (by erasing starting from
APPLICATION_ADDR).
The erase command can take some time (eg an STM32F765 with 2MB of flash
takes 8 to 10 seconds). This time is normally enough to make pydfu.py fail
with a timeout. The DFU standard includes a mechanism for the DFU device
to request a longer timeout as part of the get-status response just before
starting an operation. This timeout functionality has been implemented
here.
Before this commit the USB VCP TX ring-buffer used the basic implementation
where it can only be filled to a maximum of buffer size-1. For a 1024 size
buffer this means the largest packet that can be sent is 1023. Once a
packet of this size is sent the next byte copied in goes to the final byte
in the buffer, so must be sent as a 1 byte packet before the read pointer
can be wrapped around to the beginning. So in large streaming transfers,
watching the USB sniffer you basically get alternating 1023 byte packets
then 1 byte packets.
This commit changes the ring-buffer implementation to a scheme that doesn't
have the full-size limitation, and the USB VCP driver can now achieve a
constant stream of full-sized packets. This scheme introduces a
restriction on the size of the buffer: it must be a power of 2, and the
maximum size is half of the size of the index (in this case the index is
16-bit, so the maximum size would be 32767 bytes rounded to 16384 for a
power-of-2). But this is not a big limitation because the size of the
ring-buffer prior to this commit was restricted to powers of 2 because it
was using a mask-based method to wrap the indices.
For an explanation of the new scheme see
https://www.snellman.net/blog/archive/2016-12-13-ring-buffers/
The RX buffer could likely do with a similar change, though as it's not
read from in chunks like the TX buffer it doesn't present the same issue,
all that's lost is one byte capacity of the buffer.
USB VCP TX throughput is improved by this change, potentially doubling the
speed in certain cases.
By passing through the I2C instance to the application callbacks, the
application can implement multiple I2C slave devices on different
peripherals (eg I2C1 and I2C2).
This commit also adds a proper rw argument to i2c_slave_process_addr_match
for F7/H7/WB MCUs, and enables the i2c_slave_process_tx_end callback.
Mboot is also updated for these changes.
Signed-off-by: Damien George <damien@micropython.org>
Mboot now supports FAT, LFS1 and LFS2 filesystems, to load firmware from.
The filesystem needed by the board must be explicitly enabled by the
configuration variables MBOOT_VFS_FAT, MBOOT_VFS_LFS1 and MBOOT_VFS_LFS2.
Boards that previously used FAT implicitly (with MBOOT_FSLOAD enabled) must
now add the following config to mpconfigboard.h:
#define MBOOT_VFS_FAT (1)
Signed-off-by: Damien George <damien@micropython.org>
This commit factors the code for files and streaming to separate source
files (vfs_fat.c and gzstream.c respectively) and introduces an abstract
gzstream interface to make it easier to plug in different filesystems.
Signed-off-by: Damien George <damien@micropython.org>
There's no need to do a directory listing to search for the given firmware
filename, it just takes extra time and code size. Instead this commit
changes it so that the requested firmware file is opened immediately and
will abort if the file couldn't be opened. This also allows to specify
files in a directory.
Signed-off-by: Damien George <damien@micropython.org>
Previously, if FAT was not enabled but LFS1/2 was then MICROPY_PY_IO_FILEIO
would be disabled and file binary-mode was not supported.
Signed-off-by: Damien George <damien@micropython.org>
Commit 8675858465 switched to using the CMSIS
provided SystemInit function which sets VTOR to 0x00000000 (previously it
was 0x08000000). A VTOR of 0x00000000 will be correct on some MCUs but not
on others where the built-in bootloader is remapped to this address, via
__HAL_SYSCFG_REMAPMEMORY_SYSTEMFLASH().
To make sure mboot has the correct vector table, this commit explicitly
sets VTOR to the correct value of 0x08000000.
Signed-off-by: Damien George <damien@micropython.org>
There's no need to duplicate this functionality in mboot, the code provided
in stm32lib/CMSIS does the same thing and makes it easier to support other
MCU series.
Signed-off-by: Damien George <damien@micropython.org>
The flash functions in ports/stm32/flash.c are almost identical to those in
ports/stm32/mboot/main.c, so remove the duplicated code in mboot and use
instead the main stm32 code. This also allows supporting other MCU series.
Signed-off-by: Damien George <damien@micropython.org>
This commit makes the low-level flash C functions usable by code other than
flashbdev.c (eg by mboot). Changes in this commit are:
- flash_erase() and flash_write() now return an errno error code, a
negative value on error.
- flash_erase() now automatically locks the flash, as well as unlocking it.
- flash_write() now automatically unlocks the flash, as well as locking it.
- flashbdev.c is modified for the above changes.
Signed-off-by: Damien George <damien@micropython.org>
irq.h is included by py/mphal.h but it's better to be explicit, eg if mboot
uses powerctrlboot.c.
Signed-off-by: Damien George <damien@micropython.org>
The irq.h file now just provides low-level IRQ definitions and priorities.
All Python binding definitions are moved to modmachine.h, with some
renaming of pyb -> machine, and also the machine_idle definition (was
pyb_wfi) is moved to modmachine.c.
The cc3200 and teensy ports are updated to build with these changes.
Signed-off-by: Damien George <damien@micropython.org>
There are a maximum of 8 USB endpoints and each has 2 buffer slots
(in/out). This commit add support for up to 8 endpoints and adds FIFO
configuration for USB profiles with 2xVCP on MCUs that have device-only USB
peripherals.
Tested on NUCLEO_WB55 in 2xVCP, 2xVCP+MSC and 2xVCP+MSC+HID mode.
Signed-off-by: Damien George <damien@micropython.org>
No functionality change is intended with this commit, it just consolidates
the separate implementations of GC helper code to the lib/utils/ directory
as a general set of helper functions useful for any port. This reduces
duplication of code, and makes it easier for future ports or embedders to
get the GC implementation correct.
Ports should now link against gchelper_native.c and either gchelper_m0.s or
gchelper_m3.s (currently only Cortex-M is supported but other architectures
can follow), or use the fallback gchelper_generic.c which will work on
x86/x64/ARM.
The gc_helper_get_sp function from gchelper_m3.s is not really GC related
and was only used by cc3200, so it has been moved to that port and renamed
to cortex_m3_get_sp.
Note: the uncrustify configuration is explicitly set to 'add' instead of
'force' in order not to alter the comments which use extra spaces after //
as a means of indenting text for clarity.
In mboot, the ability to override the USB vendor/product id's was added
back in 5688c9ba09. However, when the main
firmware is turned into a DFU file the default VID/PID are used there.
pydfu.py doesn't care about this but dfu-util does and prevents its use
when the VID/PID don't match.
This commit exposes BOOTLOADER_DFU_USB_VID/PID as make variables, for use
on either command line or mpconfigboard.mk, to set VID/PID in both mboot
and DFU files.
Add -Wdouble-promotion and -Wfloat-conversion for most ports to ban out
implicit floating point conversions, and add extra Travis builds using
MICROPY_FLOAT_IMPL_FLOAT to uncover warnings which weren't found
previously. For the unix port -Wsign-comparison is added as well but only
there since only clang supports this but gcc doesn't.
