As I mentioned in issue #6310 while investigating that the Teensy port
did not support RS485_dir pin on normal GPIO pins, I found that it
was not implemented either as well on some other ports.
So was curious to implement it for RP2040 using same approach as I did
for the MIMXRT in the Pull Request #6328
That is I setup the specified pin as a normal GPIO pin in output mode
and then when you do a write operation it sets the GPIO pin logically
high, and when the write completes I set it logically low.
Note: knowing when I can set it low can be tricky, as you need to make
sure the full output has completed otherwise the data will be corrupted.
I am using: uart_tx_wait_blocking(self->uart);
Which looks like it is supposed to wait until the busy status is no
longer set, which the Reference manual mentioned, but this is leaving
the line logically set longer than I would like.
however I have tried running it with my hacked up version of the
Python Robotis DynamixelSDK and was able to talk to some AX servos.
I did have to change the library slightly for the RP2040, as the
library was erroring out when you did something like uart.read(5)
and it timed out without receiving anything. The RP2040 returned
None whereas I think the Teensy returned an empty set, which is what
it looks like the PySerial original code expects.
Not sure if anyone is interested in this, but thought i would
put it out as PR and see.
Now a 'once' and a 'loop' buffer can be specified.
'once' is useful for things like writing a neopixel strip in the background,
if you can guarantee the buffer contents are stable until the write is complete.
'loop' is useful for periodic things, like pwm & servos.
both together are useful for some special cases of pwm/servo, where a
transitional waveform needs to be played for one repetition and then
a new waveform needs to be played after that.
The API is renamed to reflect that it's a more generic 'background'
operation.
This allows you to list and explore connected USB devices. It
only stubs out the methods to communicate to endpoints. That will
come in a follow up once TinyUSB has it. (It's in progress.)
Related to #5986
This is needed so that the floppy flux reader can enable the pull up
on the index pin while using it as a pio jmp pin.
Also fixes a doc bug where the `jmp_pin` was omitted in one spot in the docs.
This tweaks the RMT timing to better match the 1/3 and 2/3 of 800khz
guideline for timing. It also ensures a delay of 300 microseconds
with the line low before reset.
Pin reset is now changed to the IDF default which pulls the pin up
rather than CircuitPython's old behavior of floating the pin.
Fixes#5679
The port is free to return NULL for any/all of these, and the caller has
to check.
This will be used in the floppy code, because aside from getting the
registers, it looks like all is independent of MCU.
This brings the pins in line with the documented [pinouts]. The only
"special" pins:
- GP0, GP1 are mentioned as the default UART, so we init them as
such and give them the TX and RX alternative names.
- GP16 is connected to the onboard neopixel DIN line and we assign it
the NEOPIXEL name. (Power of the neopixel is connected to the 3.3V
rail, not a pin. See [schematic].)
- GP26, GP27, GP28, GP29 have unambiguous ADC designations in the
[pinouts], so we assign the `A` analogue names as the Pico board
definition does.
[pinouts]: https://www.waveshare.com/wiki/RP2040-Zero#Pinouts
[schematic]: https://www.waveshare.com/w/upload/4/4c/RP2040_Zero.pdf
If, for some reason, you mix up TX and RX when calling `busio.UART` (who would do that ;) ), you get `Invalid pins`. When you go to try again, you'll get `All UART peripherals are in use` because the interface was claimed as busy before pins are verified. This should fix that issue.
This targets the 64-bit CPU Raspberry Pis. The BCM2711 on the Pi 4
and the BCM2837 on the Pi 3 and Zero 2W. There are 64-bit fixes
outside of the ports directory for it.
There are a couple other cleanups that were incidental:
* Use const mcu_pin_obj_t instead of omitting the const. The structs
themselves are const because they are in ROM.
* Use PTR <-> OBJ conversions in more places. They were found when
mp_obj_t was set to an integer type rather than pointer.
* Optimize submodule checkout because the Pi submodules are heavy
and unnecessary for the vast majority of builds.
Fixes#4314
By having a pair of buffers, the capture hardware can fill one buffer while
Python code (including displayio, etc) operates on the other buffer. This
increases the responsiveness of camera-using code.
On the Kaluga it makes the following improvements:
* 320x240 viewfinder at 30fps instead of 15fps using directio
* 240x240 animated gif capture at 10fps instead of 7.5fps
As discussed at length on Discord, the "usual end user" code will look like
this:
camera = ...
with camera.continuous_capture(buffer1, buffer2) as capture:
for frame in capture:
# Do something with frame
However, rather than presenting a context manager, the core code consists of
three new functions to start & stop continuous capture, and to get the next
frame. The reason is twofold. First, it's simply easier to implement the
context manager object in pure Python. Second, for more advanced usage, the
context manager may be too limiting, and it's easier to iterate on the right
design in Python code. In particular, I noticed that adapting the
JPEG-capturing programs to use continuous capture mode needed a change in
program structure.
The camera app was structured as
```python
while True:
if shutter button was just pressed:
capture a jpeg frame
else:
update the viewfinder
```
However, "capture a jpeg frame" needs to (A) switch the camera settings and (B)
capture into a different, larger buffer then (C) return to the earlier
settings. This can't be done during continuous capture mode. So just
restructuring it as follows isn't going to work:
```python
with camera.continuous_capture(buffer1, buffer2) as capture:
for frame in capture:
if shutter button was just pressed:
capture a jpeg frame, without disturbing continuous capture mode
else:
update the viewfinder
```
The continuous mode is only implemented in the espressif port; others
will throw an exception if the associated methods are invoked. It's not
impossible to implement there, just not a priority, since these micros don't
have enough RAM for two framebuffer copies at any resonable sizes.
The capture code, including single-shot capture, now take mp_obj_t in the
common-hal layer, instead of a buffer & length. This was done for the
continuous capture mode because it has to identify & return to the user the
proper Python object representing the original buffer. In the Espressif port,
it was convenient to implement single capture in terms of a multi-capture,
which is why I changed the singleshot routine's signature too.
At present, Adafruit's rotary encoders all move 1 quadrature cycle per
detent, so we originally hard-coded division-by-4. However, other
encoders exist, including ones without detents, ones with 2 detents per
cycle, and others with 4 detents per cycle.
The new `divisor` property and constructor argument allows selecting
a divisor of 1, 2, or 4; with the default of 4 giving backward
compatibility.
The property is not supported (yet?) on espressif MCUs; it throws an
error if a value other than 4 is set.
F-strings, new machine.I2S class, ESP32-C3 support and LEGO_HUB_NO6 board
This release of MicroPython adds support for f-strings (PEP-498), with a
few limitations compared to normal Python. F-strings are essentially
syntactic sugar for "".format() and make formatting strings a lot more
convenient. Other improvements to the core runtime include pretty printing
OSError when it has two arguments (an errno code and a string), scheduling
of KeyboardInterrupt on the main thread, and support for a single argument
to the optimised form of StopIteration.
In the machine module a new I2S class has been added, with support for
esp32 and stm32 ports. This provides a consistent API for transmit and
receive of audio data in blocking, non-blocking and asyncio-based
operation. Also, the json module has support for the "separators" argument
in the dump and dumps functions, and framebuf now includes a way to blit
between frame buffers of different formats using a palette. A new,
portable machine.bitstream function is also added which can output a stream
of bits with configurable timing, and is used as the basis for driving
WS2812 LEDs in a common way across ports.
There has been some restructuring of the repository directory layout, with
all third-party code now in the lib/ directory. And a new top-level
directory shared/ has been added with first-party code that was previously
in lib/ moved there.
The docs have seen further improvement with enhancements and additions to
the rp2 parts, as well as a new quick reference for the zephyr port.
The terms master/slave have been replaced with controller/peripheral,
mainly relating to I2C and SPI usage. And u-module references have been
replaced with just the module name without the u-prefix to help clear up
the intended usage of modules in MicroPython.
For the esp8266 and esp32 ports, hidden networks are now included in WLAN
scan results. On the esp32 the RMT class is enhanced with idle_level and
write_pulses modes. There is initial support for ESP32-C3 chips with
GENERIC_C3 and GENERIC_C3_USB boards.
The javascript port has had its Makefile and garbage collector
implementation reworked so it compiles and runs with latest the Emscripten
using asyncify.
The mimxrt port sees the addition of hardware I2C and SPI support, as well
as some additional methods to the machine module. There is also support
for Hyperflash chips.
The nrf port now has full VFS storage support, enables source-line on
traceback, and has .mpy features consistent with other ports.
For the rp2 port there is now more configurability for boards, and more
boards added.
The stm32 port has a new LEGO_HUB_NO6 board definition with detailed
information how to get this LEGO Hub running stock MicroPython. There is
also now support to change the CPU frequency on STM32WB MCUs. And USBD_xxx
descriptor options have been renamed to MICROPY_HW_USB_xxx.
Thanks to everyone who contributed to this release: Amir Gonnen, Andrew
Scheller, Bryan Tong Minh, Chris Wilson, Damien George, Daniel Mizyrycki,
David Lechner, David P, Fernando, finefoot, Frank Pilhofer, Glenn Ruben
Bakke, iabdalkader, Jeff Epler, Jim Mussared, Jonathan Hogg, Josh Klar,
Josh Lloyd, Julia Hathaway, Krzysztof Adamski, Matúš Olekšák, Michael
Weiss, Michel Bouwmans, Mike Causer, Mike Teachman, Ned Konz, NitiKaur,
oclyke, Patrick Van Oosterwijck, Peter Hinch, Peter Züger, Philipp
Ebensberger, robert-hh, Roberto Colistete Jr, Sashkoiv, Seon Rozenblum,
Tobias Thyrrestrup, Tom McDermott, Will Sowerbutts, Yonatan Goldschmidt.
What follows is a detailed list of changes, generated from the git commit
history, and organised into sections.
Main components
===============
all:
- fix signed shifts and NULL access errors from -fsanitize=undefined
- update to point to files in new shared/ directory
py core:
- mpstate: make exceptions thread-local
- mpstate: schedule KeyboardInterrupt on main thread
- mperrno: add MP_ECANCELED error code
- makeqstrdefs.py: don't include .h files explicitly in preprocessing
- mark unused arguments from bytecode decoding macros
- objexcept: pretty print OSError also when it has 2 arguments
- makeversionhdr: add --tags arg to git describe
- vm: simplify handling of MP_OBJ_STOP_ITERATION in yield-from opcode
- objexcept: make mp_obj_exception_get_value support subclassed excs
- support single argument to optimised MP_OBJ_STOP_ITERATION
- introduce and use mp_raise_type_arg helper
- modsys: optimise sys.exit for code size by using exception helpers
- objexcept: make mp_obj_new_exception_arg1 inline
- obj: fix formatting of comment for mp_obj_is_integer
- emitnative: reuse need_reg_all func in need_stack_settled
- emitnative: ensure stack settling is safe mid-branch
- runtime: fix bool unary op for subclasses of native types
- builtinimport: fix condition for including do_execute_raw_code()
- mkrules: automatically build mpy-cross if it doesn't exist
- implement partial PEP-498 (f-string) support
- lexer: clear fstring_args vstr on lexer free
- mkrules.mk: do submodule sync in "make submodules"
extmod:
- btstack: add missing call to mp_bluetooth_hci_uart_deinit
- btstack: check that BLE is active before performing operations
- uasyncio: get addr and bind server socket before creating task
- axtls-include: add axtls_os_port.h to customise axTLS
- update for move of crypto-algorithms, re1.5, uzlib to lib
- moduselect: conditionally compile select()
- nimble: fix leak in l2cap_send if send-while-stalled
- btstack/btstack.mk: use -Wno-implicit-fallthrough, not =0
- utime: always invoke mp_hal_delay_ms when >= to 0ms
- modbluetooth: clamp MTU values to 32->UINT16_MAX
- nimble: allow modbluetooth binding to hook "sent HCI packet"
- nimble: add "memory stalling" mechanism for l2cap_send
- uasyncio: in open_connection use address info in socket creation
- modujson: add support for dump/dumps separators keyword-argument
- modlwip: fix close and clean up of UDP and raw sockets
- modbluetooth: add send_update arg to gatts_write
- add machine.bitstream
- modframebuf: enable blit between different formats via a palette
lib:
- tinyusb: update to version 0.10.1
- pico-sdk: update to version 1.2.0
- utils/stdout_helpers: make mp_hal_stdout_tx_strn_cooked efficient
- axtls: switch to repo at micropython/axtls
- axtls: update to latest axtls 2.1.5 wih additional commits
- re1.5: move re1.5 code from extmod to lib
- uzlib: move uzlib code from extmod to lib
- crypto-algorithms: move crypto-algorithms code from extmod to lib
- update README's based on contents of these dirs
drivers:
- neopixel: add common machine.bitstream-based neopixel module
- neopixel: optimize fill() for speed
- neopixel: reduce code size of driver
- cyw43: fix cyw43_deinit so it can be called many times in a row
- cyw43: make wifi join fail if interface is not active
mpy-cross:
- disable stack check when building with Emscripten
Support components
==================
docs:
- library: document new esp32.RMT features and fix wait_done
- library: warn that ustruct doesn't handle spaces in format strings
- esp8266/tutorial: change flash mode from dio to dout
- replace master/slave with controller/peripheral in I2C and SPI
- rp2: enhance quickref and change image to Pico pinout
- rp2: update general section to give a brief technical overview
- library/utime.rst: clarify behaviour and precision of sleep ms/us
- library/uasyncio.rst: document stream readexactly() method
- library/machine.I2S.rst: fix use of sd pin in examples
- zephyr: add quick reference for the Zephyr port
- library/zephyr: add libraries specific to the Zephyr port
- templates: add unix and zephyr quickref links to top-index
- rename ufoo.rst to foo.rst
- replace ufoo with foo in all docs
- library/index.rst: clarify module naming and purpose
- library/builtins.rst: add module title
- library/network.rst: simplify socket import
- add docs for machine.bitstream and neopixel module
- library: fix usage of :term: for frozen module reference
- esp8266: use monospace for software tools
- reference: mention that slicing a memoryview causes allocation
examples: no changes specific to this component/port
tests:
- extmod: make uasyncio_heaplock test more deterministic
- cpydiff/modules_struct_whitespace_in_format: run black
- extmod/ujson: add tests for dump/dumps separators argument
- run-multitests.py: add broadcast and wait facility
- multi_bluetooth/ble_subscribe.py: add test for subscription
- extmod/vfs_fat_finaliser.py: ensure alloc at never-used GC blocks
- basics: split f-string debug printing to separate file with .exp
- pybnative: make while.py test run on boards without pyb.delay
tools:
- autobuild: add scripts to build release firmware
- remove obsolete build-stm-latest.sh script
- ci.sh: run apt-get update in ci_powerpc_setup
- makemanifest.py: allow passing flags to mpy-tool.py
- autobuild: add mimxrt port to build scripts for nightly builds
- pyboard.py: add cmd-line option to make soft reset configurable
- mpremote: swap order of PID and VID in connect-list output
- ci.sh: build unix dev variant as part of macOS CI
- ci.sh: build GENERIC_C3 board as part of esp32 CI
- autobuild: use separate IDF version to build newer esp32 SoCs
- autobuild: add FeatherS2 and TinyS2 to esp32 auto builds
- mpremote: add seek whence for mounted files
- mpremote: raise OSError on unsupported RemoteFile.seek
- autobuild: add the MIMXRT1050_EVKB board to the daily builds
- ci.sh: add mpy-cross build to nrf port
- codeformat.py: include ports/nrf/modules/nrf in code formatting
- gen-cpydiff.py: don't rename foo to ufoo in diff output
- autobuild: add auto build for Silicognition wESP32
- mpremote: fix connect-list in case VID/PID are None
- mpremote: add "devs" shortcut for "connect list"
- mpremote: remove support for pyb.USB_VCP in/out specialisation
- autobuild: don't use "-B" for make, it's already a fresh build
- pyboard.py: move --no-exclusive/--soft-reset out of mutex group
- pyboard.py: make --no-follow use same variable as --follow
- pyboard.py: add --exclusive to match --no-exclusive
- pyboard.py: make --no-soft-reset consistent with other args
- uncrustify: force 1 newline at end of file
- mpremote: bump version to 0.0.6
CI:
- workflows: add workflow to build and test javascript port
- workflows: switch from Coveralls to Codecov
- workflows: switch from lcov to gcov
- workflows: add workflow to build and test unix dev variant
The ports
=========
all ports:
- use common mp_hal_stdout_tx_strn_cooked instead of custom one
- update for move of crypto-algorithms, uzlib to lib
- rename USBD_VID/PID config macros to MICROPY_HW_USB_VID/PID
bare-arm port: no changes specific to this component/port
cc3200 port: no changes specific to this component/port
esp8266 port:
- add __len__ to NeoPixel driver to support iterating
- Makefile: add more libm files to build
- include hidden networks in WLAN.scan results
- replace esp.neopixel with machine.bitstream
- remove dead code for end_ticks in machine_bitstream
esp32 port:
- boards/sdkconfig.base: disable MEMPROT_FEATURE to alloc from IRAM
- add __len__ to NeoPixel driver to support iterating
- main: allow MICROPY_DIR to be overridden
- esp32_rmt: fix RMT looping in newer IDF versions
- esp32_rmt: enhance RMT with idle_level and write_pulses modes
- add new machine.I2S class for I2S protocol support
- machine_spi: calculate actual attained baudrate
- machine_hw_spi: use a 2 item SPI queue for long transfers
- machine_dac: add MICROPY_PY_MACHINE_DAC option, enable by default
- machine_i2s: add MICROPY_PY_MACHINE_I2S option, enable by default
- fix use of mp_int_t, size_t and uintptr_t
- add initial support for ESP32C3 SoCs
- boards/GENERIC_C3: add generic C3-based board
- modmachine: release the GIL in machine.idle()
- mphalport: always yield at least once in delay_ms
- machine_uart: add flow kw-arg to enable hardware flow control
- boards: add Silicognition wESP32 board configuration
- mpconfigport.h: enable reverse and inplace special methods
- include hidden networks in WLAN.scan results
- makeimg.py: get bootloader and partition offset from sdkconfig
- enable MICROPY_PY_FSTRINGS by default
- machine_hw_spi: release GIL during transfers
- machine_pin: make check for non-output pins respect chip variant
- replace esp.neopixel with machine.bitstream
- remove dead code for end_ticks in machine_bitstream
- boards: add GENERIC_C3_USB board with USB serial/JTAG support
javascript port:
- rework Makefile and GC so it works with latest Emscripten
- Makefile: suppress compiler errors from array bounds
- Makefile: change variable to EXPORTED_RUNTIME_METHODS
mimxrt port:
- move calc_weekday helper function to timeutils
- machine_spi: add the SPI class to the machine module
- moduos: seed the PRNG on boot using the TRNG
- boards: set vfs partition start to 1 MBbyte
- main: skip running main.py if boot.py failed
- main: extend the information returned by help()
- mimxrt_flash: remove commented-out code
- modmachine: add a few minor methods to the machine module
- machine_led: use mp_raise_msg_varg helper
- machine_i2c: add hardware-based machine.I2C to machine module
- add support for Hyperflash chips
- boards: add support for the MIMXRT1050_EVKB board
- machine_pin: implement ioctl for Pin
minimal port:
- Makefile: add support for building with user C modules
nrf port:
- modules: replace master/slave with controller/peripheral in SPI
- boards/common.ld: calculate unused flash region
- modules/nrf: add new nrf module with flash block device
- drivers: add support for using flash block device with SoftDevice
- mpconfigport.h: expose nrf module when MICROPY_PY_NRF is set
- README: update README.md to reflect internal file systems
- mpconfigport.h: tune FAT FS configuration
- Makefile: add _fs_size linker script override from make
- modules/uos: allow a board to configure MICROPY_VFS_FAT/LFS1/LFS2
- mpconfigport.h: enable MICROPY_PY_IO_FILEIO when an FS is enabled
- qstrdefsport.h: add entries for in-built FS mount points
- main: add auto mount and auto format hook for internal flash FS
- boards: enable needed features for FAT/LFS1/LFS2
- facilitate use of freeze manifest
- boards: set FROZEN_MANIFEST blank when SD present on nrf51 targets
- modules/scripts: add file system formatting script
- Makefile: set default manifest file for all targets
- mphalport: add dummy function for mp_hal_time_ns()
- boards: enable MICROPY_VFS_LFS2 for all target boards
- modules/uos: add ilistdir to uos module
- modules/nrf: add function to enable/disable DCDC
- enable source line on tracebacks
- set .mpy features consistent with documentation and other ports
pic16bit port: no changes specific to this component/port
powerpc port: no changes specific to this component/port
qemu-arm port: no changes specific to this component/port
rp2 port:
- use 0=Monday datetime convention in RTC
- machine_rtc: in RTC.datetime, compute weekday automatically
- CMakeLists.txt: suppress compiler errors for pico-sdk and tinyusb
- tusb_config.h: set CFG_TUD_CDC_EP_BUFSIZE to 256
- machine_uart: add hardware flow control support
- machine_uart: allow overriding default machine UART pins
- machine_i2c: allow boards to configure I2C pins using new macros
- machine_spi: allow boards to configure SPI pins using new macros
- machine_uart: fix poll ioctl to also check hardware FIFO
- machine_uart: fix read when FIFO has chars but ringbuf doesn't
- tusb_port: allow boards to configure USB VID and PID
- boards/ADAFRUIT_FEATHER_RP2040: configure custom VID/PID
- boards/ADAFRUIT_FEATHER_RP2040: configure I2C/SPI default pins
- boards/SPARKFUN_PROMICRO: configure UART/I2C/SPI default pins
- boards/SPARKFUN_THINGPLUS: configure I2C/SPI default pins
- boards: add Adafruit ItsyBitsy RP2040
- boards: add Adafruit QT Py RP2040
- boards: add Pimoroni Pico LiPo 4MB
- boards: add Pimoroni Pico LiPo 16MB
- boards: add Pimoroni Tiny 2040
- CMakeLists.txt: allow a board's cmake to set the manifest path
- enable MICROPY_PY_FSTRINGS by default
- Makefile: add "submodules" target, to match other ports
- rp2_flash: disable IRQs while calling flash_erase/program
- CMakeLists.txt: add option to enable double tap reset to bootrom
- mpconfigport.h: allow boards to add root pointers
samd port:
- add support for building with user C modules
stm32 port:
- softtimer: add soft_timer_reinsert() helper function
- mpbthciport: change from systick to soft-timer for BT scheduling
- provide a custom BTstack runloop that integrates with soft timer
- usb: make irq's default trigger enable all events
- boardctrl: skip running main.py if boot.py had an error
- sdio: fix undefined reference to DMA stream on H7
- dma: add DMAMUX configuration for H7 to fix dma_nohal_init
- main: call mp_deinit() at end of main
- adc: allow using ADC12 and ADC3 for H7
- adc: define the ADC instance used for internal channels
- adc: simplify and generalise how pin_adcX table is defined
- add new machine.I2S class for I2S protocol support
- boards/NUCLEO_F446RE: fix I2C1 pin assignment to match datasheet
- replace master/slave with controller/peripheral in I2C and SPI
- systick: always POLL_HOOK when delaying for milliseconds
- sdram: make SDRAM test cache aware, and optional failure with msg
- boards/NUCLEO_F446RE: enable CAN bus support
- boards: add support for SparkFun STM32 MicroMod Processor board
- uart: fix LPUART1 baudrate set/get
- uart: support low baudrates on LPUART1
- boards/STM32F429DISC: set correct UART2 pins and add UART3/6
- boards/NUCLEO_F439ZI: add board definition for NUCLEO_F439ZI
- boards/LEGO_HUB_NO6: add board definition for LEGO_HUB_NO6
- Makefile: update to only pull in used Bluetooth library
- README.md: update supported MCUs, and submodule and mboot use
- usbd_desc: rename USBD_xxx descriptor opts to MICROPY_HW_USB_xxx
- usbd_cdc_interface: rename USBD_CDC_xx opts to MICROPY_HW_USB_xx
- powerctrl: support changing frequency on WB MCUs
- boards/NUCLEO_H743ZI2: add modified version of NUCLEO_H743ZI
- mbedtls: fix compile warning about uninitialized val
- enable MICROPY_PY_FSTRINGS by default
- add implementation of machine.bitstream
- Makefile: allow GIT_SUBMODULES and LIBS to be extended
- stm32_it: support TIM17 IRQs on WB MCUs
- disable computed goto on constrained boards
- storage: make extended-block-device more configurable
- boards/LEGO_HUB_NO6: change SPI flash storage to use hardware SPI
- boards/LEGO_HUB_NO6: skip first 1MiB of SPI flash for storage
- boards/LEGO_HUB_NO6: add make commands to backup/restore firmware
teensy port: no changes specific to this component/port
unix port:
- modffi: add option to lock GC in callback, and cfun access
- Makefile: add back LIB_SRC_C to list of object files
- variants: enable help and help("modules") on standard and dev
- Makefile: disable error compression on arm-linux-gnueabi-gcc
windows port:
- Makefile: add .exe extension to executables name
- appveyor: update to VS 2017 and use Python 3.8 for build/test
zephyr port:
- machine_spi: add support for hardware SPI
I noticed that the loop over 65535 possible denominators took a long time,
causing up to 100ms wait for a sound sample to start playing!
This algorithm, adapted from an algorithm shown in Python's fractions.py,
is guaranteed to find the best denominator in a small number of steps
(I think log2-many steps but I'm not sure). In practice, it means the time
between samples playing is just 10ms, and some of that is recreating the
sine wave sample in Python each time.
It often finds the same solution as the old code, but sometimes it finds
one a bit better since it compares the ratios using float point instead
of integer arithmetic.
