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AN672

PRECISION32™ SI32LIBRARY OVERVIEW

Silicon Laboratories 

AN672

8. I/O Component

COMPONENT: si32IoComponent

REQUIRES: si32BaseComponent, si32ObjectComponent

PROVIDES: si32IoObject, si32PortalObject, si32TimerObject

The si32IoComponent contains objects that abstract the behavior of hardware. Derived objects in

si32McuComponent implement hardware specific concrete instances of these objects.

8.1. si32PortalObject

In general, there are several types of streaming I/O operations possible:

Non-blocking Synchronous: Reads return immediately with an actual count of 0 or more, up to the

desired count, depending on how much data is available (i.e., hardware receive FIFO). Writes return

immediately with an actual count of 0 or more, up to the desired count, depending on how much space is

available (i.e., hardware transmit FIFO).

Non-blocking Asynchronous: Reads/writes take a callback and return immediately. The callback may be

invoked before the read/write call returns. The callback always indicates completion, and the actual count

is always the desired count unless there was an error or the request was aborted.

Blocking Synchronous: Reads/writes do not return until the full desired count has been moved or an

error occurs.

Blocking Asynchronous: Essentially the same as non-blocking asynchronous, except that it is possible

for reads/writes to block before returning, even after the callback has been invoked.

The si32Library portal objects implement un-buffered, non-blocking, synchronous and asynchronous operations.

They are designed to be as simple as possible in that they do not require other library objects or components. In

other words, si32UsartAPortalObject is derived from si32PortalObject but does not depend on other objects such

as timers, queues, buffers, pseudo-threads, or run-loops. This means that portals do not implement timeouts, they

do not implement transmit/receive queues, they do not support multiple sessions, and they do not offer blocking

operations. Additional entities are required in order to support those functionalities and are outside of the scope of

portals. Note that portals do implement operations to abort reads/writes in progress, enabling timeout/error

handlers to regain control of the underlying hardware.

Asynchronous operations on portal objects typically invoke the callback from interrupt dispatch level. The callback

function must restrict its behavior to only perform interrupt- (and possibly thread-) safe operations. Ensuring correct

behavior of callbacks is outside of the scope of the portal objects.

Figure 12 shows the si32PortalObject diagram.

si32RootObject

si32PortalObject

SI32_XXX_X_Type

Figure 12. si32PortalObject Diagram

Rev. 0.1

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