Gregory's ServerThis photo shows part of the shift matrix with the sloping polysilicon control lines (green) and transistors (dark boxes). The diagram shows how three of the control lines are wired. 7/11
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 At the input to the shifter, latch circuits hold the two input words from the register file. The circuit can also swap the two values. The photos show the circuit on the die. Left shows the metal layers; right shows the underlying silicon with the transistors. 9/11 There are complications, of course. The matrix outputs 37 bits, not 32, for reasons. Supporting bytes and 16-bit shifts needs more circuitry as does rotating through the carry. For more on the 386's barrel shifter, see my blog post: https://www.righto.com/2023/12/386-barrel-shifter.html 10/11 |
This circuit shifts from 0 to 3 bits. It passes the input bit straight through or sends it two positions to the right. Next, it passes that bit straight through or passes it one position to the right. Thus each bit is shifted right 0 to 3 positions. 8/11