Commit graph

13 commits

Author SHA1 Message Date
Joe Finney
857a626ed0 microbit: Memory Optimisation Mega Update
This release contains a widespread set of updates and optimisations to the micro:bit
runtime, with a view to reducing the SRAM footprint of the whole system. This is to
provide as much usable HEAP storage for application programs as possible.

Specific updates and optimisations include:

  - Additional compilation flags to allow the core micro:bit runtime to be configured.
    These are defined in MicroBitConfig.h

  - A custom heap allocator. This is now included for two reasons:

    1) To provide a simple mechanism to to utilise both the mbed heap space and other memory
       regions (such as unused memory in the SoftDevice region) as a single virtual heap.
    2) To address some issues that have been noted that are attributable to heap fragmentation.
       The micro:bit heap allocator has a simple algorithm, but one that is chosen to respond
       well to the relativelt high 'heap churn' found in the micro:bit environment.

    All micro:bit components and user programs now use this heap allocator trasparently.

  - Updates to BLE services to remove persistent references to their GATT services. This consumes
    vast amounts SRAM, rather unecessarily. Instead only handles to the relevant GATT characteristics
    are now stored. This specifically includes:
      + MicroBitDFUService
      + MicroBitEventService
      + DeviceInformationService

  - Updates to the Fiber scheduler to save SRAM. More specifically:
      + Removed the need to hold an empty processor context to intialise fibers.
      + The IDLE fiber now runs without a stack
      + fiber stacks are now only created when a fiber is descheduled for the first time, thereby reducing heap churn.
      + the 'main' fiber is now recycled into the fiber_pool if it leaves app_main()
      + fibers created through invoke() now only maintains the necessary part of teh parent stack that is needed, thereby
        reducing the stack size of spawned fibers.

  - Updates to the Message Bus to reduce the overall memory footprint of processing events. More specifically:
      + Event handlers are now always called using invoke(), such that non-blocking event handlers no longer need
        a dedicated fiber to execute - thereby saving SRAM and processor time.
      + Processing of events from the event queue is now rate paced. Events only continue to be processed as long as there
        are no fibers on the run queue. i.e. event processing is no longer greedy, thereby reducing the number of fibers
        created on the runqueue.

  - Updates to BLUEZOENE code to bring up core BLE services even if they are not enabled by default. This allows
    programs that do not require BLE to operate to benefit from the full range of SRAM, whilst still allowing the
    device to be programmed over BLE.

  - Updates to the Soft Device initialisation configuration, reducing the size of the GATT table held in the top 1.8K
    of its 8K memory region to around 800 bytes. This is sufficient to run the default set of BLE services on the micro:bit
    so the additional memory is configured as HEAP storage by MicroBitHeapAllocator.

  - Minor changes to a range of components to integrate with the above changes.
    + rename of free() to release() in DynamicPWM to avoid namespace collision with MicroBitHeap free()
    + rename of fork_on_block to invoke() to enhance readbility.

  - Many code cleanups and updates to out of date comments.
2015-08-31 23:25:10 +01:00
Joe Finney
42f43b2255 Merge branch 'master' of https://github.com/lancaster-university/microbit-dal 2015-08-19 23:48:36 +01:00
Joe Finney
0fec4ae87c microbit: BUGFIX - Input validation in MicroBitDisplay::setBrightness()
Updates to MicroBitDisplay::setBrightness() to perform a NOP for out of bound parameters.
This aligns the functionality of the runtime with the TD simulator.
2015-08-19 23:36:17 +01:00
Joe Finney
58d24ab0a8 microbit: Updated MicroBitMessageBus to use fork_on_block functionality
Updates the MicroBitMessageBus implementation to use fork_on_block() calls rather
than create_fiber() calls when servicing events. This provides greater optimisation
for non-blocking event handlers.

More specifically, this update:

 - Replaces calls to create_fiber() ith fork_on_block during event send operations.
 - Adds a queue of events, to ensure events generated from interrupt context are not serviced in interrupt context.
 - Registers a listener with the idle process to empty the event queue.
2015-08-19 23:35:45 +01:00
Joe Finney
f4b8a1a272 microbit: Added fork_on_block functionality to fiber scheduler
The microbit fiber scheduler is often used to service event handlers by the microbit message bus.
This provides a very elegant decoupling of user code from system code, interrupt handlers and
also allows users to make blocking calls within event handlers. However, many event handlers are
non-blocking, so launching a dedicated fiber is wasteful in terms of time and SRAM.

This patch adds fork_on_block() to the scheduler. Inspired by the UNIX copy_on_write
technique, this optimisation is semantically equivalent to a create_fiber() call, but will first attempt
to execute the given function in the context of the currently running fiber, and *only* create a fiber
if the given code attempts a blocking operation.

More specifically, this update:

 - adds fork_on_block() functions for parameterised and non-parameterised functions.
 - adds fields to the fiber context to record the status of parent/child fibers.
 - adds optimised ASM functions to store and restore Cortex M0 register context.
 - adds a utility function to determine if the processor is executing in interrupt context.
 - updates to sleep() and wait_for_event() to handle fork_on_block semantics.
 - minor code optimsations within the scheduler.
2015-08-19 23:27:26 +01:00
Jonathan Protzenko
c4656ca855 Add a missing operator to ManagedType. 2015-08-18 17:49:08 -07:00
Jonathan Protzenko
6e65c33e88 Expose PinName for PWM purposes. 2015-08-14 15:51:16 -07:00
James Devine
7e8e6778d7 microbit-dal: Added readme.md
This read me describes the process of getting the microbit environment working with yotta.
2015-08-14 17:29:00 +01:00
James Devine
3ef5901c5b microbit-dal: added a reset mechanism to uBit
Users can now call uBit.reset() to reset the device.
2015-08-14 16:51:45 +01:00
James Devine
d7b3ba9dab microbit-dal: Fixed a bug on printing a character with a delay
Previously when a blocking print finished, the animatemode was not
reset, which meant sometimes there would be a race condition.
2015-08-14 01:06:41 +01:00
James Devine
f8ebfc69fb microbit-dal: added #define to determine BLE usage
NO_BLE can now be defined to determine whether ble
will be brought up or not at initialisation of uBit.
This is especially useful for two new Yotta targets:
bbc-microbit-classic-gcc-nosd,
bbc-microbit-classic-armcc-nosd, which do not use
softdevice.
2015-08-13 00:49:48 +01:00
James Devine
0552741cf1 microbit-dal: updated module.json
Updated module.json to point to lancaster-university organisation
repos.
2015-08-12 16:08:02 +01:00
James Devine
538e1c48bd microbit-dal: Initial Commit
This is the first commit of the microbit-dal on GitHub.
This repository contains the runtime, which is a light
weight operating system developed by Lancaster University.
2015-08-12 11:53:41 +01:00