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* 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. * SPI0Command - A utility function for generic SPI commands on SPI0 The rom code does not support some flash functions, or have a generic way of sending custom commands to the flash chip. In particular XMC flash chips have a third status register, and the ROM only supports two. There are also certain requirements for using SPI0 such as waiting for the flash to be idle and not allowing your code to trigger a flash cache miss while using SPI0. * Clean some trailing spaces * Upgrade _SPI0Command to _SPICommand We needed to assess the SPI registers as base+offset to avoid referring to the registers using constant addresses as these addresses were loaded from flash and had the potential to trigger a flash cache miss. For similar reasons functions need to be called via function pointers stored in RAM. Also avoid constants in FLASH, use a copy stored in RAM. As a side effect we can now select which controller to access as a parameter. * Tidy up a comment thats no longer applicable * Comments, formatting and variable renames Added a number of comments to better explain the code and improved the formatting. Also renamed some variables for consistency. * put SPI0Command in namespace experimental * Add a comment noting that the code has only been tested on bus 0 * Replace use of memcpy with for loops in _SPICommand() memcpy is not guaranteed to be safe (IRAM_ATTR or ROM) like I thought. As a bonus the for loop is guaranteed to do 32-bit wide transfers, unlike memcpy. * Typo fix what happens when you forget to edit after copy/paste * Move the SpiOpResult enum into experimental namespace