Author: wmb Date: Wed Aug 10 00:58:17 2011 New Revision: 2454 URL: http://tracker.coreboot.org/trac/openfirmware/changeset/2454
Log: x86 timestamp counter calibration loop needs a slightly longer sensing window to prevent miscalibration.
Modified: cpu/x86/pc/tsccal1.fth
Modified: cpu/x86/pc/tsccal1.fth ============================================================================== --- cpu/x86/pc/tsccal1.fth Wed Aug 10 00:42:06 2011 (r2453) +++ cpu/x86/pc/tsccal1.fth Wed Aug 10 00:58:17 2011 (r2454) @@ -24,7 +24,12 @@ al ah mov h# 40 # al in al ah xchg - d# 5 # ax cmp + \ The number 10 below gives a sufficient window to ensure that a count + \ value in the range from 0 to 9 is seen. The process of latching the + \ timer and reading the value is time-consuming because I/O port access + \ is slow, comparable to the clock that drives the ticker. For many + \ systems, a value of 5 is enough, but I have seen systems that need 8. + d# 10 # ax cmp < until
h# f c, h# 31 c, \ Get time-stamp counter value into DX,AX