existence of {read,write}-twice registers

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jeffythedragonslayer
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existence of {read,write}-twice registers

Post by jeffythedragonslayer »

Does anyone know the hardware design reason why some SNES registers are write-twice or read-twice? Is it just a tradeoff to reduce the number of registers at the expense of extra instructions?
calima
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Re: existence of {read,write}-twice registers

Post by calima »

The early on-planned NES compat counts for some, otherwise it's likely money saving.
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jeffythedragonslayer
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Re: existence of {read,write}-twice registers

Post by jeffythedragonslayer »

Yeah I heard after NES compatibility was dropped the SNES still retained a lot of the architecture. The bottom answer here sounds good but I feel like it would be pretty hard to write a half-completed 16-bit update bug on the NES, with it being an 8-bit system, so this answer is probably explaining the new registers introduced with the SNES:

https://retrocomputing.stackexchange.co ... for-the-sn
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