| /****************************************************************************** |
| * Filename: group_aon_doc.h |
| * Revised: 2016-03-30 13:03:59 +0200 (Wed, 30 Mar 2016) |
| * Revision: 45971 |
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| //! \addtogroup aon_group |
| //! @{ |
| //! \section sec_aon Introduction |
| //! |
| //! The Always-ON (AON) voltage domain contains the AUX power domain, AON power domain, and JTAG power domain. |
| //! The AON API includes functions to access the AON power domain. For functions accessing the AUX power domain |
| //! see the [AUX API](@ref aux_group). |
| //! |
| //! The AON power domain contains circuitry that is always enabled, except for the shutdown mode |
| //! (digital supply is off), and the AON power domain is clocked at 32-kHz. |
| //! |
| //! The AON API accesses the AON registers through a common module called AON Interface (AON IF) which handles the |
| //! actual transactions towards the much slower AON registers. Because accessing AON can cause a significant |
| //! delay in terms of system CPU clock cycles it is important to understand the basics about how the AON IF |
| //! operates. The following list describes a few of the most relevant properties of the AON IF seen from the system CPU: |
| //! - \ti_bold{Shadow registers}: The system CPU actually accesses a set of "shadow registers" which are being synchronized to the AON registers |
| //! by the AON IF every AON clock cycle. |
| //! - Writing an AON register via AON IF can take up to one AON clock cycle before taking effect in the AON domain. However, the system CPU can |
| //! continue executing without waiting for this. |
| //! - The AON IF supports multiple writes within the same AON clock cycle thus several registers/bit fields can be synchronized simultaneously. |
| //! - Reading from AON IF returns the value from last time the shadow registers were synchronized (if no writes to AON IF have occurred since) |
| //! thus the value can be up to one AON clock cycle old. |
| //! - Reading from AON IF after a write (but before synchronization has happened) will return the value from the shadow register |
| //! and not the last value from the AON register. Thus doing multiple read-modify-writes within one AON clock cycle is supported. |
| //! - \ti_bold{Read delay}: Due to an asynchronous interface to the AON IF, reading AON registers will generate a few wait cycles thus stalling |
| //! the system CPU until the read completes. There is no delay on writes to AON IF if using posted/buffered writes. |
| //! - \ti_bold{Synchronizing}: If it is required that a write to AON takes effect before continuing code execution it is possible to do a conditional "wait for |
| //! synchronization" by calling \ref SysCtrlAonSync(). This will wait for any pending writes to synchronize. |
| //! - \ti_bold{Updating}: It is also possible to do an unconditional "wait for synchronization", in case a new read |
| //! value is required, by calling \ref SysCtrlAonUpdate(). This is typically used after wake-up to make sure the AON IF has been |
| //! synchronized at least once before reading the values. |
| //! |
| //! Below are a few guidelines to write efficient code for AON access based on the properties of the interface to the AON registers. |
| //! - Avoid synchronizing unless required by the application. If synchronization is needed then try to group/arrange AON writes to |
| //! minimize the number of required synchronizations. |
| //! - If modifying several bit fields within a single AON register it is slightly faster to do a single read, modify the bit fields, |
| //! and then write it back rather than doing multiple independent read-modify-writes (due to the read delay). |
| //! - Using posted/buffered writes to AON (default) lets the system CPU continue execution immediately. Using non-posted/non-buffered |
| //! writes will generate a delay similar to a read access. |
| //! |
| //! @} |