Eurosoft Product Advisory
Testing Tips from Eurosoft
Issues with the CMOS Checksum Test
Some of you may have seen issues with the CMOS Checksum test failing in Pc-Check Windows.
In some cases, when the system is booted for the first time the CMOS checksum has not been correctly set in the BIOS.
When the CMOS Checksum Test is executed the checksum is calculated and compare it to the value stored in the BIOS.
As shown in the example below, when some systems are in an unused state, the checksum stored in the BIOS is not the same as the calculated checksum.
The CMOS Checksum Test reads the Checksum and calculates an independent result.
Example A ; Test Machine 1–Before
CMOS Checksums: Read:C001 Calc:0FE6
CalcSub:0FA6 CMOS Date: 28/6/2013 13:14:0
After simply entering the BIOS and then doing save and close, the BIOS recalculates the checksum and then the value stored is the same as the calculation that we perform in the diagnostics.
Example B – Test Machine 1-After_CSM_Toggled.
CMOS Checksums: Read:0FE6 Calc:0FE6
CalcSub:0FA6 CMOS Date: 28/6/2013 13:26:57
The BIOS contains a diagnostic bit that can be set so that when the motherboard with an invalid checksum was booted, the BIOS would show the message “CMOS Checksum Error Press F1 to continue”. Pressing F1 to continue would again cause the recalculation of the checksum. If the diagnostic bit has not been set by the manufacturer the motherboard can boot with an invalid checksum and subsequently fail the CMOS Checksum Test.
This issue may appear to be a very minor as it is easily resolved and you may not see the issue at all if changing a BIOS setting is part of your process. However, there are potential issues that could affect users in other ways. For example, some BIOS flash tools read the checksums and do not work if the checksum is not valid. This could cause end users to contact your service department for assistance. It is also possible that this could cause issues with certain copy protection methods employed by software vendors.
Many of you will not see this issue; you will only see this issue if your motherboard manufacturer is not shipping motherboards with the correct CMOS checksum or if they do not set the diagnostic bit so that the system recognises at first boot that the checksum is invalid and thus forces a recalculation.