crc

问题 Upd. See the end of post for working code I'm already mad with this. How can I make checksum from CRC unit on stm32f103 match with software implementation? Stm has polynom 0x04C11DB7 and reset value 0xFFFFFFFF . So I've tried to calculate it in python. Code for stm: uint32_t crc32_hard_block(uint32_t *buf, uint32_t len) { CRC_ResetDR(); uint32_t crc = CRC_CalcBlockCRC(buf, len); return crc; } uint32_t buf[4] = {50, 10, 243, 147}; uint32_t crc_hard_block = crc32_hard_block(buf, 4); Code for

问题 I know the whole intention of using CRC is to do error detection, but I heard someone state that it can be used to do basic error correction in addition to error detection. I was curious if this was the case, and if so, how powerful is it? I mean, we usually refer to CRC as capable of performing x-bit detection, but I'm curious if it is capable of performing x-bit correction. If so, how does this work? Thanks. 回答1: It is possible to do single-bit error correction with a CRC. Assume one has a

问题 I know the whole intention of using CRC is to do error detection, but I heard someone state that it can be used to do basic error correction in addition to error detection. I was curious if this was the case, and if so, how powerful is it? I mean, we usually refer to CRC as capable of performing x-bit detection, but I'm curious if it is capable of performing x-bit correction. If so, how does this work? Thanks. 回答1: It is possible to do single-bit error correction with a CRC. Assume one has a

问题 I need to calculate a CRC-64 using this setup into this wonderful website: http://www.sunshine2k.de/coding/javascript/crc/crc_js.html As you can see I require "input reflected" and that means that I need to reverse the bit order of any byte (a bit annoying). For the moment, I implemented this with a lookup table (for example 0x55 -> 0xAA), but I was wondering if there is any property of CRC which can be used to be more efficient. This is my code (in C): static const unsigned long long CRC64

问题 Normally one would add a CRC to the end of the data stream. The CRC check would include the CRC itself and return 0 if the CRC is correct. I need to add a CRC to verify my embedded code. It needs to be checked in place, but the top word in memory space is for an interrupt vector. Is it possible to place a key value midstream such that the CRC check returns 0 for the whole code? (or is this unsolvable?) 回答1: It's definitely possible. You can run a CRC backwards, which would be fast and easy.

问题 Why we need to invert crc? In which cases we need to do this? (invert mean crc = ~crc ) Is it defence from zero cases (when whole message is consists of zeros)? How it helps in this case? 回答1: You mean invert, or take the one's complement. (Reverse would mean swapping the order of the bits, undoing a CRC calculation, or reverse-engineering the CRC parameters.) That is done when the CRC parameters are defined that way. See this list of CRCs, where those with xorout defined as all 1's are

问题 I had some contact with the CRC-16 checksum in the past and was accustomed to verifying it by recalculating the CRC-16 checksum over the file I want to verify, plus the 2 bytes of the CRC-16 itself. If the result was zero, then the file integrity was valid, otherwise not. This can be coded very efficiently like with the following pseudo-C: if (recalculated_crc16_checksum != 0) // Error: file integrity is corrupt else // Success: file integrity is valid I recently wanted to use the CRC-32

问题 Where I can find this crc32() function in detail? I saw this Link but I couldn't figure out how CRC is being calculated. I asked a question about updating the CRC based on the data stream instead of waiting to have all the data. I got the answer as follows (Thanks to @MarkAdler): unsigned long crc = crc32(0, NULL, 0); // initial CRC for (...) { // some sort of loop ... // generating a chunk of data crc = crc32(crc, buf, len); // update the CRC with the data ... // this all gets repeated many

问题 How does the probability of undetected error vary as a function of link type ? are they related at all? I mean if the link is lossy or has a higher bit error rate how this would affect the Undetected Error Probability? Is there any formula to calculate that? 回答1: What you really mean by "link type" is the error characteristics of the channel. On a channel with a high bit error rate, e.g. the number of bits in the CRC ( n ) in error somewhere in each message (where each messages gets a CRC),

问题 How does the probability of undetected error vary as a function of link type ? are they related at all? I mean if the link is lossy or has a higher bit error rate how this would affect the Undetected Error Probability? Is there any formula to calculate that? 回答1: What you really mean by "link type" is the error characteristics of the channel. On a channel with a high bit error rate, e.g. the number of bits in the CRC ( n ) in error somewhere in each message (where each messages gets a CRC),