[SPI & XIP] add high-speed SPI mode option #251
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when enabled SPI clock runs at half of processor clock
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This PR adds a "high-speed" SPI mode to the SPI and the XIP module. When enabled, the default three-bit clock prescaler select is ignored and the SPI clock operates at maximum speed, which is half of the processor clock (
processor_clk / 2). Note: using only the clock prescaler select the maximum SPI clock frequency isprocessor_clk / 4.To enable the high-speed SPI mode a new flag has been added to the modules control register (those bits were previously unused):
NEORV32_SPI.CTRLbit 16 "SPI_CTRL_HIGHSPEED"NEORV32_XIP.CTRLbit 26 "XIP_CTRL_HIGHSPEED"High-speed mode enable and disable functions have been added to the according software libraries.
✔️ This PR is fully backwards-compatible.