RIOT-OS uses part of Espressif ESP8266 RTOS SDK to build support for
this CPU. The SDK includes some vendor-provided closed source
pre-compiled libraries that we need to modify to adapt to RIOT-OS
usage. This library modifications was done once and uploaded to a fork
of the vendor repository and was provided as an environment variable.
This patch changes two things:
1. It installs the SDK as a RIOT PKG from the new pkg/esp8266_sdk
directory instead of requiring the user to download it separately.
2. It performs the library modifications (symbol renames) on the pkg
Makefile removing the need to use a fork with the modifications applied
and simplifying the SDK update and future modifications.
This change sets the SDK package version (git SHA) to the same one that
our fork was using as a parent in the vendor repository, meaning that
the output libraries are exactly the same as before.
Tested with
```
ESP8266_RTOS_SDK_DIR=/dev/null USEMODULE=esp_log_startup make -C tests/shell BOARD=esp8266-esp-12x flash
```
and verified that the program works. The boot message now includes:
```
ESP8266-RTOS-SDK Version v3.1-51-g913a06a9
```
confirming the SDK version used.
`/dev/null` in the test is just to make sure that no evaluation of
`ESP8266_RTOS_SDK_DIR` in make is affected by the environment variable
value which would be set to the SDK for people who followed the set up
instructions before this change.
Tested the checkout size:
```bash
$ du -hs build/pkg/esp8266_sdk/
124M build/pkg/esp8266_sdk/
```
The esp8266 CPU has actually two hardware UART peripherals. UART0 is
used by the boot ROM for flashing and serial output during boot,
typically at a baudrate of 74880 bps until the bootloader or application
sets the more standard 115200 baudrate. This UART0 device has two
possible pins for TXD, GPIO1 and GPIO2, which are both set to TXD by the
boot ROM. esp8266 modules will typically have GPIO1 labeled as the TX
pin, but it is possible to use GPIO2 for that purpose even while
flashing the device with esptool.py.
The second device, UART1, also has two options for TXD, GPIO2 and GPIO7,
and only one option for RXD, GPIO8. However, GPIO7 and GPIO8 are used
by the flash internally so those options are not very useful unless
maybe while running from IRAM with the flash disabled, for example for
a debugger over UART1.
This patch allows boards to override UART{0,1}_{R,T}XD in their
periph_conf.h to configure the uart selection. Defining UART1_TX will
make the UART_DEV(1) device available.
Tested with:
```CFLAGS='-DUART1_TXD=GPIO2' make -C tests/periph_uart BOARD=esp8266-esp-12x flash term```
* Connected one USB-UART to the standard GPIO1 and GPIO3 for flashing
and console. After flashing we see the manual test output at 115200
bps
* Connected a second USB-UART with RX to GPIO2 running at 74880.
Then run on the first console:
```
> init 1 74880
> send 1 hello
```
The word "hello" appears on the second UART connection.
Note that GPIO2 is used during boot for UART0's TX until the application
or bootloader set it to a regular GPIO, so some boot ROM messages at
74880 bps are visible. After running `init 1 74880` it is set to UART1's
TX.
To be able to define common configurations for all ESP CPUs, the CPU specific configuration cpu_conf.h has to include a common configuration. For that purpose cpu_conf.h in cpu/esp_common is renamed to cpu_conf_common.h and included in CPU specific configurations.
cpu/esp8266/include/periph_cpu.h overrides the default definition of adc_res_t from periph/adc with a definition which contains only one resolution. This gives compilation errorss if an application uses other resolutions. According to the documentation, adc_sample should return -1 if the resolution is not supported. All other CPUs override adc_res_t either to add new resolutions or to mark resolutions as unsupported. But they all allow to use them at the interface. Therefore, esp8266 uses now the default definition of adc_res_t and returns -1 if a solution is used in adc_sample that is not supported.
