micropython升级到了 1.9.1，主要改进有：

v1.9.1   修复了 stm32 的 USB 存储, lwIP 绑定和 VFS 问题

    This release provides an important fix for the USB mass storage device in
    the stmhal port by implementing the SCSI SYNCHRONIZE_CACHE command, which
    is now require by some Operating Systems.  There are also fixes for the
    lwIP bindings to improve non-blocking sockets and error codes.  The VFS has
    some regressions fixed including the ability to statvfs the root.
    
    All changes are listed below.
    
    py core:
    - modbuiltins: add core-provided version of input() function
    - objstr: catch case of negative "maxsplit" arg to str.rsplit()
    - persistentcode: allow to compile with complex numbers disabled
    - objstr: allow to compile with obj-repr D, and unicode disabled
    - modsys: allow to compile with obj-repr D and PY_ATTRTUPLE disabled
    - provide mp_decode_uint_skip() to help reduce stack usage
    - makeqstrdefs.py: make script run correctly with Python 2.6
    - objstringio: if created from immutable object, follow copy on write policy
    
    extmod:
    - modlwip: connect: for non-blocking mode, return EINPROGRESS
    - modlwip: fix error codes for duplicate calls to connect()
    - modlwip: accept: fix error code for non-blocking mode
    - vfs: allow to statvfs the root directory
    - vfs: allow "buffering" and "encoding" args to VFS's open()
    - modframebuf: fix signed/unsigned comparison pendantic warning
    
    lib:
    - libm: use isfinite instead of finitef, for C99 compatibility
    - utils/interrupt_char: remove support for KBD_EXCEPTION disabled
    
    tests:
    - basics/string_rsplit: add tests for negative "maxsplit" argument
    - float: convert "sys.exit()" to "raise SystemExit"
    - float/builtin_float_minmax: PEP8 fixes
    - basics: convert "sys.exit()" to "raise SystemExit"
    - convert remaining "sys.exit()" to "raise SystemExit"
    
    unix port:
    - convert to use core-provided version of built-in import()
    - Makefile: replace references to make with $(MAKE)
    
    windows port:
    - convert to use core-provided version of built-in import()
    
    qemu-arm port:
    - Makefile: adjust object-file lists to get correct dependencies
    - enable micropython.mem_*() functions to allow more tests
    
    stmhal port:
    - boards: enable DAC for NUCLEO_F767ZI board
    - add support for NUCLEO_F446RE board
    - pass USB handler as parameter to allow more than one USB handler
    - usb: use local USB handler variable in Start-of-Frame handler
    - usb: make state for USB device private to top-level USB driver
    - usbdev: for MSC implement SCSI SYNCHRONIZE_CACHE command
    - convert from using stmhal's input() to core provided version
    
    cc3200 port:
    - convert from using stmhal's input() to core provided version
    
    teensy port:
    - convert from using stmhal's input() to core provided version
    
    esp8266 port:
    - Makefile: replace references to make with $(MAKE)
    - Makefile: add clean-modules target
    - convert from using stmhal's input() to core provided version
    
    zephyr port:
    - modusocket: getaddrinfo: Fix mp_obj_len() usage
    - define MICROPY_PY_SYS_PLATFORM (to "zephyr")
    - machine_pin: use native Zephyr types for Zephyr API calls
    
    docs:
    - machine.Pin: remove out_value() method
    - machine.Pin: add on() and off() methods
    - esp8266: consistently replace Pin.high/low methods with .on/off
    - esp8266/quickref: polish Pin.on()/off() examples
    - network: move confusingly-named cc3200 Server class to its reference
    - uos: deconditionalize, remove minor port-specific details
    - uos: move cc3200 port legacy VFS mounting functions to its ref doc
    - machine: sort machine classes in logical order, not alphabetically
    - network: first step to describe standard network class interface
    
    examples:
    - embedding: use core-provided KeyboardInterrupt object

http://micropython.org/resources/micropython-ChangeLog.txt

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