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ARMmbed / mbed-drivers

Drivers for common MCU peripherals in mbed OS.
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Clarify memory model for transaction queues #9

Open bogdanm opened 9 years ago

bogdanm commented 9 years ago

This is related to pull request #5: there is now a SPI module class which has a transaction queue object. The transaction queue is fixed in size for each instance of the peripheral; currently, there are 16 transactions in the queue for each SPI instance. This seems rather arbitrary and wasteful in terms of RAM. Variants:

  1. keep the transaction queue fixed in size, but make the maximum size global per peripheral type, not per peripheral instance (for example: maximum 32 transactions for all SPI instances). Not ideal.
  2. make the transaction queue dynamic (new transactions are malloc'd)
  3. combine 1 and 2 by starting with a fixed size and growing it only if needed

In the context of this issue, it might be worth investigating if it's worth using some C++ std classes (vector, array ...).

bremoran commented 9 years ago

This seems like a perfect case for a slab allocator. Do we have one?

0xc0170 commented 9 years ago

Nope, we don't yet. Let's discuss this topic this week