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AX = DA01h CL = subfunction (00h-02h) 00h set low CPU speed 01h set high CPU speed 02h get current CPU speed
Return:
CF clear if successful AH = current/new CPU speed (00h low, 01h high) AL = ??? (00h) CF set on error AH = error code (86h unsupported subfunction)
Notes: In the v1.00.05.AX1 BIOS, subfunctions 00h and 01h are NOPs in both protected and V86 modes due to a test of MSW bit 0. Setting the CPU speed also generates the same audible signals generated when manually switching speeds with Ctrl-Alt-Gray- and Ctrl-Alt-Gray+
BUG: The BIOS apparently intends to return CF set if ???, but fails to use a different exit path in that case, resulting in CF clear
Category: Vendor-specific BIOS Extensions - Int 15h - A
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