This is a good board to demonstrate the use of Mboot because it only has a
USB HS port exposed so the native ST DFU mode cannot be used. With Mboot
this port can be used.
If a custom bootloader is enabled (eg mboot) then machine.bootloader() will
now enter that loader. To get the original ST DFU loader pass any argument
to the function, like machine.bootloader(1).
Don't exclude the Timer instance 1 entry from machine_timer_obj[] when
using soft PWM. The usage is already checked when creating the Timer,
so just create an empty entry.
If needed these parameters can be added back and made functional one at a
time. It's better to explicitly not support them than to silently allow
but ignore them.
Python defines warnings as belonging to categories, where category is a
warning type (descending from exception type). This is useful, as e.g.
allows to disable warnings selectively and provide user-defined warning
types. So, implement this in MicroPython, except that categories are
represented just with strings. However, enough hooks are left to implement
categories differently per-port (e.g. as types), without need to patch each
and every usage.
With clock bypass enabled the attached SD card is clocked at the maximum
48MHz. But some SD cards are unreliable at these rates. Although it's
nice to have high speed transfers it's more important that the transfers
are reliable for all cards. So disable this clock bypass option.
This way the UART REPL does not need the MicroPython heap and exists
outside the MicroPython runtime, allowing characters to still be received
during a soft reset.
Auto-detection of the crystal frequency is convenient and allows for a
single binary for many different boards. But it can be unreliable in
certain situations so in production, for a given board, it's recommended to
configure the correct fixed frequency.
Configuration for the build is now specified using sdkconfig rather than
sdkconfig.h, which allows for much easier configuration with defaults from
the ESP IDF automatically applied. sdkconfig.h is generated using the new
ESP IDF kconfig_new tool written in Python. Custom configuration for a
particular ESP32 board can be specified via the make variable SDKCONFIG.
The esp32.common.ld file is also now generated using the standard ESP IDF
ldgen.py tool.
When the ESP IDF builds a project it puts all separate components into
separate .a library archives. And then the esp32.common.ld linker script
references these .a libraries by explicit name to put certain object files
in iRAM.
This patch does a similar thing for the custom build system used here,
putting all IDF .o's into their respective .a. So a custom linker script
is no longer needed.
ISR's no longer need to be in iRAM, and the ESP IDF provides an option to
specify that they are in iRAM if an application needs lower latency when
handling them. But we don't use this feature for user interrupts: both
timer and gpio ISR routines are registered without the ESP_INTR_FLAG_IRAM
option, and so the scheduling code no longer needs to be in iRAM.
