3 ms·

That reminds me of the time a shiny new enterpricey ethernet switch delayed a release of Red Hat Linux until we figured out that it was happily corrupting packe

by bcrl 3y ago

That reminds me of the time a shiny new enterpricey ethernet switch delayed a release of Red Hat Linux until we figured out that it was happily corrupting packets and fixing up the CRC and checksum causing certain stress tests being run over NFS to fail randomly. It turns out that sometimes hardware devs don't actually design for the level of reliability expected by customers in their hardware.

tzs 3y ago
Sounds similar to something I hit at work once. I built a release of one of our products and uploaded the binary to a file server on our Ethernet LAN for the test department to test, but the upload failed. Everything else I tried to upload worked. I found I could also not transfer that file to anything else over Ethernet. After some experimenting I determined that there was a particular 4 byte (if I remember the length correctly) string that simply could not be sent or received by my Ethernet card. Some searching turned up something on some obscure support forum where the maker of that card admitted that there was a bug in the hardware's checksum implementation that made it fail on that byte pattern. A friend of mine in college had an interesting hardware data corruption bug on a computer he built for his project in the microprocessor lab we both took in 1982. We did a joint project, where together we designed a small 68k based system and then separately each built a copy. Here's mine [1] [2]. On mine the serial ports worked fine up to 19200 bps (the limit of the ADM3a terminals we were using). On his once you got past 2400 bps it started getting errors. That nature of the errors was such that only a subset of the possible ASCII characters could be sent. Characters outside that subset would be replaced by characters from the subset. The faster you went the smaller the working subset. What happened was that there were filter capacitors on the serial lines to filter out high frequency noise. My filter capacitors were correct. His were not. When he had went to the EE stockroom to buy filter capacitor they gave him capacitors that were a couple of orders of magnitude bigger than he asked for. On his system then if a character with too many bit transitions or bit transitions to close together those looked like high frequency noise to the filter capacitors and were filtered out. [1] https://imgur.com/Ts9wcfW https://imgur.com/Ts9wcfW [2] https://imgur.com/3D4rvdC https://imgur.com/3D4rvdC

by bcrl 3y ago

tzs 3y ago

Sounds similar to something I hit at work once. I built a release of one of our products and uploaded the binary to a file server on our Ethernet LAN for the test department to test, but the upload failed. Everything else I tried to upload worked. I found I could also not transfer that file to anything else over Ethernet. After some experimenting I determined that there was a particular 4 byte (if I remember the length correctly) string that simply could not be sent or received by my Ethernet card. Some searching turned up something on some obscure support forum where the maker of that card admitted that there was a bug in the hardware's checksum implementation that made it fail on that byte pattern. A friend of mine in college had an interesting hardware data corruption bug on a computer he built for his project in the microprocessor lab we both took in 1982. We did a joint project, where together we designed a small 68k based system and then separately each built a copy. Here's mine [1] [2]. On mine the serial ports worked fine up to 19200 bps (the limit of the ADM3a terminals we were using). On his once you got past 2400 bps it started getting errors. That nature of the errors was such that only a subset of the possible ASCII characters could be sent. Characters outside that subset would be replaced by characters from the subset. The faster you went the smaller the working subset. What happened was that there were filter capacitors on the serial lines to filter out high frequency noise. My filter capacitors were correct. His were not. When he had went to the EE stockroom to buy filter capacitor they gave him capacitors that were a couple of orders of magnitude bigger than he asked for. On his system then if a character with too many bit transitions or bit transitions to close together those looked like high frequency noise to the filter capacitors and were filtered out. [1] https://imgur.com/Ts9wcfW https://imgur.com/Ts9wcfW [2] https://imgur.com/3D4rvdC https://imgur.com/3D4rvdC