CRC Error Messages on Multiple-Processor Computers

When you use a remote access server to transfer data over a null modem cable between a multiple-processor computer and a singe-processor computer, you may receive cyclical redundancy check (CRC) or data overrun error messages in Dial-Up Monitor.

The overruns were occurring because the internal buffers in the UART (FIFO's) filled up before the interrupt was serviced and data was lost on the RS-232 bus. Further debugging found that the serial interrupt is masked for longer than .087 ms by the IDE interrupts that were being serviced.

There are a couple of settings in the registry that will allow the interrupts to be serviced quicker, set RxFIFO to 1: HKLM\System\CurrentControlSet\Services\Serial By default DMA is not enabled on Windows NT. Once enabling DMA the problem was resolved. I was able to increase the baud rate to 115k and transfer over 100 meg of data with no errors. Enabling improves CPU utilization over standard PIO, increasing system usability while IDE operations are in progress.

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

Using PCI bus master DMA, the CPU has to service only a single interrupt that is generated when the IDE command completes. This is compared to standard PIO, where the CPU has to service an interrupt from the device, every time a block of data becomes available to the host. Performance figures on a checked build showed approximately 20 to 30 percent CPU utilization using DMA, versus approximately 90 to 100 percent utilization during PIO transfers. Performance figures for DMA on a free build are even better, showing single-digit percentages in some cases. How to Obtain Dmacheck.exe for Windows NT [winnt] ID: Q191774 CREATED: 24-AUG-1998 MODIFIED: 24-AUG-1998 WinNT:4.0 For more information about downloading files from the Microsoft Download Center, please see the following article in the Microsoft Knowledge Base: ARTICLE-ID: Q119591 TITLE : How to Obtain Microsoft Support Files from Online Services The following motherboards have exhibited the behavior described in this article:

• Asus P2l97-DS with the Intel 440LX chip set
• Micronics Helios with the Intel 440BX chip set
• SuperMicro P6DBS with the Intel 440BX chip set
• Tyan S1686D with the Intel 440FX chip set
• Tyan S1832D with the Intel 440BX chip set
• Tyan S1563 with the Intel 430HX chip set

All these motherboards use the Intel I/O APIC multiple-processor S82093AA controller.