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Patterns in Register Map Design

posted by janrinok on Monday May 22, @05:31PM   

owl writes:

https://www.devever.net/~hl/regmap

If you've ever had to write a program which interfaces directly with hardware — perhaps while writing a program for an MCU or embedded system or a kernel driver — you may have noticed a few common patterns in register map behaviour and design. I'm not sure anyone has ever really collected them together, so I decided to make a list of all the ones I can think of.

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Original Submission

• Re:Write-Only Registers Re:Write-Only Registers (Score: 4, Informative) by sjames on Monday May 22, @11:15PM (1 child)

  by sjames (2882) on Monday May 22, @11:15PM (#1307502) Journal

  In addition, a zero register is a good way to initialize an accumulator without having an extra instruction. Writing to the zero register is a cheap to implement NOP. Add that to the inexpensive addressing flexibility and you get a lot of bang for the buck from the zero register.

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• Re:Write-Only Registers (Score: 3, Informative) by owl on Tuesday May 23, @02:17AM

  by owl (15206) on Tuesday May 23, @02:17AM (#1307527)

  Now that you mention it, I think the Alpha's "nop" instruction was actually something like

  add r0,r0,r0

  (assuming r0 was the "always zero" register), that would add zero to zero and store the answer in the register that was always zero. The result, a "NOP" instruction, without having to explicitly have an actual "NOP" instruction built into the hardware.

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