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README.md: Add note about callback execution speed.

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@ -109,7 +109,7 @@ under development so check for updates.
4.1 [Class methods](./README.md#41-class-methods) 4.1 [Class methods](./README.md#41-class-methods)
4.2 [Constructor](./README.md#42-constructor) 4.2 [Constructor](./README.md#42-constructor)
4.3 [Callback methods](./README.md#43-callback-methods) Methods which run in response to events. 4.3 [Callback methods](./README.md#43-callback-methods) Methods which run in response to events.
4.4 [Method](./README.md#44-method) Optional interface to uasyncio code. 4.4 [Method](./README.md#44-method) Optional interface to asyncio code.
4.5 [Class variable](./README.md#45-class-variable) Control latency caused by garbage collection. 4.5 [Class variable](./README.md#45-class-variable) Control latency caused by garbage collection.
4.6 [Usage](./README.md#46-usage) Accessing data created in a screen. 4.6 [Usage](./README.md#46-usage) Accessing data created in a screen.
5. [Window class](./README.md#5-window-class) 5. [Window class](./README.md#5-window-class)
@ -161,8 +161,8 @@ under development so check for updates.
# 1. Basic concepts # 1. Basic concepts
Internally `micro-gui` uses `uasyncio`. It presents a conventional callback Internally `micro-gui` uses `asyncio`. It presents a conventional callback
based interface; knowledge of `uasyncio` is not required for its use. Display based interface; knowledge of `asyncio` is not required for its use. Display
refresh is handled automatically. Widgets are drawn using graphics primitives refresh is handled automatically. Widgets are drawn using graphics primitives
rather than icons. This makes them efficiently scalable and minimises RAM usage rather than icons. This makes them efficiently scalable and minimises RAM usage
compared to icon-based graphics. It also facilitates the provision of extra compared to icon-based graphics. It also facilitates the provision of extra
@ -529,7 +529,7 @@ The consequence of inadequate speed is that brief button presses can be missed.
This is because display update blocks for tens of milliseconds, during which This is because display update blocks for tens of milliseconds, during which
time the pushbuttons are not polled. This can be an issue in displays with a time the pushbuttons are not polled. This can be an issue in displays with a
large number of pixels, multi-byte colors and/or slow SPI clock rates. In high large number of pixels, multi-byte colors and/or slow SPI clock rates. In high
resolution cases the device driver has specfic `uasyncio` support whereby the resolution cases the device driver has specfic `asyncio` support whereby the
driver yields to the scheduler a few times during the refresh.Currently this driver yields to the scheduler a few times during the refresh.Currently this
exists on ILI9486, ILI9341 and ST7789 (e.g. TTGO T-Display). By my calculations exists on ILI9486, ILI9341 and ST7789 (e.g. TTGO T-Display). By my calculations
and measurements this should be unnecessary on other drivers, but please report and measurements this should be unnecessary on other drivers, but please report
@ -567,7 +567,7 @@ These are listed to enable users to check for newer versions or to read docs:
A copy of the official driver for OLED displays using the SSD1306 chip is A copy of the official driver for OLED displays using the SSD1306 chip is
provided. The link is to the official file. provided. The link is to the official file.
* [Synchronisation primitives](https://github.com/peterhinch/micropython-async/tree/master/v3/primitives). * [Synchronisation primitives](https://github.com/peterhinch/micropython-async/tree/master/v3/primitives).
The link is to my `uasyncio` support repo. The link is to my `asyncio` support repo.
* [PCD8544/Nokia 5110](https://github.com/mcauser/micropython-pcd8544.git). * [PCD8544/Nokia 5110](https://github.com/mcauser/micropython-pcd8544.git).
Displays based on the Nokia 5110 (PCD8544 chip) require this driver. It is not Displays based on the Nokia 5110 (PCD8544 chip) require this driver. It is not
provided in this repo. The link is to its source. provided in this repo. The link is to its source.
@ -643,7 +643,7 @@ minimal and aim to demonstrate a single technique.
"forward" button. "forward" button.
* `primitives.py` Use of graphics primitives. * `primitives.py` Use of graphics primitives.
* `aclock.py` An analog clock using the `Dial` vector display. Also shows * `aclock.py` An analog clock using the `Dial` vector display. Also shows
screen layout using widget metrics. Has a simple `uasyncio` task. screen layout using widget metrics. Has a simple `asyncio` task.
* `tbox.py` Text boxes and user-controlled scrolling. * `tbox.py` Text boxes and user-controlled scrolling.
* `tstat.py` A demo of the `Meter` class with data sensitive regions. * `tstat.py` A demo of the `Meter` class with data sensitive regions.
* `menu.py` A multi-level menu. * `menu.py` A multi-level menu.
@ -3345,16 +3345,16 @@ The `primitives.py` demo provides a simple example.
## Callbacks ## Callbacks
Callback functions should execute quickly, otherwise screen refresh will be Callback functions should execute quickly, otherwise screen refresh will not
delayed until the callback is complete. Where a time consuming task is to be occur until the callback is complete. Where a time consuming task is to be
triggered by a callback an `asyncio` task should be launched. In the following triggered by a callback an `asyncio` task should be launched. In the following
sample an `LED` widget is to be cycled through various colors in response to sample an `LED` widget is to be cycled through various colors in response to
a callback. a callback.
```python ```python
def callback(self, button, val): def callback(self, button, val):
asyncio.create_task(self.flash_led()) self.reg_task(self.flash_led(), on_change=True)
async def flash_led(self): async def flash_led(self): # Will be cancelled if the screen ceases to be current
self.led.color(RED) self.led.color(RED)
self.led.value(True) # Turn on LED self.led.value(True) # Turn on LED
await asyncio.sleep_ms(500) await asyncio.sleep_ms(500)
@ -3364,9 +3364,13 @@ async def flash_led(self):
await asyncio.sleep_ms(500) await asyncio.sleep_ms(500)
self.led.value(False) # Turn it off. Task is complete. self.led.value(False) # Turn it off. Task is complete.
``` ```
The `callback()` executes fast, with the `flash_led()` running as a background The `callback()` executes fast, with `flash_led()` running as a background task.
task. For more information on asyncio, see The use of [reg_task](./README.md#44-method)
[the tutorial](https://github.com/peterhinch/micropython-async/blob/master/v3/docs/TUTORIAL.md). is because `flash_led()` is a method of the `Screen` object accessing bound
objects. The method ensures that the task is cancelled if the user closes or
overlays the current screen. For more information on `asyncio`, see the
[official docs](https://docs.micropython.org/en/latest/library/asyncio.html)
and [tutorial](https://github.com/peterhinch/micropython-async/blob/master/v3/docs/TUTORIAL.md).
###### [Contents](./README.md#0-contents) ###### [Contents](./README.md#0-contents)