Rational: the periph_common module is required by (most) other periph drivers
and also during startup of the CPU/MCU to run periph_init. The latter is only
required if other periph drivers are used, hence periph_common should be a
depency of periph_* modules and *not* of the CPU/MCU. This PR fixes that
by making periph_common a depency of periph_* and removing the explicit
include in the CPU/MCU implementation.
PREFLASHER/PREFFLAGS/FLASHDEPS are evaluated by the main Makefile.include.
Their value does not need to be exported.
Testing
-------
`git diff --word-diff` only reports `export` being removed.
`git show --stat` reports `16 insertions(+), 16 deletions(-)`
Which is the same amount as lines that where matching
`export[[:blank::]]\+VARIABLE` plus the newline that is said to have
changed.
FLASHER and FFLAGS are evaluated by the main Makefile.include or by file
included by it. Their value does not need to be exported.
This will also prevent evaluating 'PORT' for FFLAGS when not needed.
Testing
-------
`git diff --word-diff` only reports `export` being removed.
`git show --stat` reports `84 insertions(+), 84 deletions(-)`
Which is the same amount as lines that where matching
`export[[:blank::]]\+VARIABLE`.
`top_of_stack` isn't aligned down to the previous 16 byte aligned address. Furthermore, `top_of_stack` as well as `XT_CP_SIZE` are used unaligned in `cpu/esp_common/vendor/xtensa/portasm.S` in the address computation for the coprocessor save area, .
Aligning pointer `p` down to the previous 16 byte aligned address results in a wrong address of the coprocessor save area during the initialization of the thread context. This leads to wrong values and wrong positions of these values in the coprocessor save area in inital thread context.
Since ESP8266 doesn't have a coprocessor, this bug affects only ESP32.
Calling the initialization function ensures that the dummy lwIP library is used instead of the real lwIP, even if the esp_wifi module for esp8266 is not used.
The documentation had to be changed due to the relation of module `esp_now` to `esp_wifi` module. In addition, a number of corrections have been made. In the case of documentation, it is impossible to do this in various commits.
Usually, all .rodata sections are placed in RAM by the Espressif SDK since IROM (flash) access requires 32-bit word aligned reads. thanks to the LoadStoreError exception handler from esp-open-rtos which is used now in RIOT-OS, it is also possible to place .rodata sections in IROM (flash) to save RAM resources.
Usually, the access to the IROM (flash) memory requires 32-bit word aligned reads. Attempts to access data in the IROM (flash) memory less than 32 bits in size triggers a LoadStoreError exception. With the exception handler from esp-open-rtos it becomes possible to access data in IROM (flash) with a size of less than 32 bits and thus to place .rodata sections in the IROM (flash).
Checking by the send function that at least two maximum size Ethernet frames fit in the remaining heap before the LwIP packet buffer is allocated seems to increase stability. This can be caused by the fact that WLAN hardware interrupts allocate additional memory when receiving a frame during the send attempt.
The situation where the firmware `lwIP` packet buffer is exhausted is an important indication that the traffic sent to and sent from the esp8266 is more than the esp8266 is able to handle. Therefore, it should be an error message.
It is not necessary to realize timeout handling in send function or to disconnect from AP if lwIP packet buffer is exhausted. Waiting that the frame allocated in lwIP packet buffer is freed by MAC layer led to the complete blockage of send function on heavy network load. Disconnecting from AP is counterproductive since reconnecting usually fails on heavy network load.
Disconnecting from the AP in the send function if the lwIP packet buffer is exhausted is counterproductive since reconnecting usually fails on heavy network load. A better strategy is to slow down the sending of MAC frames from netif a bit to wait for flushing the buffer in the MAC layer.
Defines a number of lwIP functions that are required as symbols by Espressif's SDK libraries. These functions are only dummies without real functionality. Using these functions instead of real lwIP functions provided with the SDK saves arround 4 kBytes of RAM.
Since _esp_wifi_recv_cb is not executed in interrupt context but in the context of the `ets` thread, it is not necessary to pass the`NETDEV_EVENT_ISR` event first. Instead, the receive function can be called directly which result in much faster handling, a less frame lost rate and more robustness.
Since _esp_wifi_recv_cb is not executed in interrupt context but in the context of the `ets` thread, the receive function can be called directly. There is no need for a mutex anymore to synchronize the access to the receive buffer between _esp_wifi_recv_cb and _recv function.
When the size of a received frame is checked, always the total length should be used instead of the length of the first lwIP pbuf in the pbuf chain. Otherwise, the check that the length does not exceed ETHERNET_MAX_LEN will always be true since the maximum size of one lwIP pbuf in a pbuf chain is 512 bytes.
Although only the station interface is needed, the WiFi interface has to be used in SoftAP + Station mode. Otherwise the send function blocks sporadically. Since the SoftAP interface is not used, it is configured with a hidden SSID and a long beacon interval. Connections from other stations are not allowed.
Some SDK interrupt service routines obviously use malloc/free in the interrupt context. Because the rmutex-based lock/unlock approach of the malloc/free function suite of the newlib does not work in the interrupt context, the SDK memory management functions MUST therefore be used. To use the same memory management functions in RIOT as in the SDK, the malloc/free function suite has to be replaced by wrapper functions.
