About the instruction execution speed

Question

Hello ~ 
 I saw the following information while referring to the document(R01US0015EJ0230 rev 2.30 page 40). 
 "Remark This number of clocks is for when the program is in the internal ROM (flash memory) area. When fetching an instruction from the internal RAM area, the number of clocks is four times the number of clocks plus 6, maximum. " In general, I know that when the code is performed in Ram, the execution speed is faster than flash XIP. However, in renesas RL78, I am confused to see that performing instruction in Ram is four times slower than performing in flash. 
 Did I misunderstand the document?

AZ [Renesas] · Accepted Answer

No, F23 or F24 do not have a dual bank flash.

JimB · Answer

I believe only the RL78/I1C device (non-automotive 512KB for meter applications) has the dual-bank flash feature. Unfortunately this has not been incorporated into the automotive devices yet. 
 Perhaps the coming 512KB F25 auto device would have this feature, but that is just a guess since it is not yet released and I don't have access to such early information. 
 One other point to note about the F23/F24 devices, for some very strange reason the RFD T02 code-flash programming does not support the feature to deactivate all interrupt vectors and use a single common ISR located in RAM for all interrupts (for the Gen1 X1x devices this was the FSL_ChangeInterruptTable function). The somewhat similar flash technology RL78 Gen-2 X2x non-auto devices do support this with the T01 version of RFD (with function R_RFD_ChangeInterruptVector). 
 This means that it is impossible to service interrupts during code-flash erase / programming operations with the F2x devices. I cannot imagine why this feature is missing, but I would certainly want that ability if I were writing a boot-loader or needed to otherwise program the code-flash.

Fragero · Answer

Code execution from RAM is faster for MPUs using external non-volatile memory to store the application. In such cases the application is copied from external memory to RAM during boot-process. In case of RL78 code execution is typically done directly from internal Flash Memory and no copying is necessary. Code execution from RAM is only necessary in special uses cases, e.g. self-programming of the Flash Memory. The RL78 RAM is optimized for fast data-access and the Flash memory for fast code execution. Your understanding of the manual is correct, Code execution from RAM is slower than from FLASH in case of RL78.

About the instruction execution speed

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