[rtl] instruction prefetch buffer (IPB) improvements #455
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add override: if C ISA extension is enabled and the IP depth is configured to be "1", the IPB size is overriden to auto-configure an IPB depth of 2
make sure IPB=1 gets auto-changed to IPB=2 as C ISA extension is enabled
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The
CPU_IPB_ENTRIESgeneric (defining the depth of the instruction prefetch buffer) can now be as small as "1". If theCISA extensions is enabled andCPU_IPB_ENTRIES = 1is configured, the actual IPB depth is set to "2" automatically (as this is required for handling unaligned 32bit instructions).Configuring
CPU_IPB_ENTRIES = 1allows reduced hardware utilization. The exemplary hardware implementation results have been updated accordingly.