Mike Nix 692e542d58 precache() - preload code into the flash cache. (#6628) ...

* precache() - preload code into the flash cache.

By preloading code into the flash cache we can take control over when
SPI Flash reads will occur when code is executing.
This can be useful where the timing of a section of code is extremely
critical and we don't want random pauses to pull code in from the SPI
flash chip.

It can also be useful for code that accesses/uses SPI0 which is connected
to the flash chip.

Non interrupt handler code that is infrequently called but might otherwise
require being in valuable IRAM - such as bit-banging I/O code or some code
run at bootup can avoid being permanently in IRAM.

Macros are provided to make precaching one or more blocks of code in any
function easy.

* Fix missing include

* Make precache extern "C"

* Attempt 2 at making precache extern "C"

* Fix calculation of number of cache lines to preload

With certain alignments/lengths of code it was possible to not read enough
into the flash cache.

This commit makes the length calculation clearer and adds an extra cache
line to ensure we precache enough code.

* Add noinline to PRECACHE_ATTR macro

Precached code needs to be noinline to ensure the no-reorder-blocks is applied.

2019-11-03 05:23:36 -03:00

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esp8266

precache() - preload code into the flash cache. (#6628)

2019-11-03 05:23:36 -03:00