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app:using_analogtest [2022/03/02 14:51] – Consolidated duplicate headers flan | app:using_analogtest [2022/03/02 15:09] – [How exactly does this work?] wordsmithing; added some explanation flan | ||
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A floppy drive is an analog device and not a digital one. It reads an analog signal from the floppy disk and sends a pulse every time it sees the signal change. (The floppy drive controller has the job of turning those pulses into digital bits.) Various drive models used various combinations of read amplifiers, filtering, and a good smattering of assumptions about the incoming signal in order to send pulses at the appropriate time, These components help the drive determine if a signal is happening "too fast" and should be ignored, or "too slow" and we should turn up the amplifier because it must be missing some data. | A floppy drive is an analog device and not a digital one. It reads an analog signal from the floppy disk and sends a pulse every time it sees the signal change. (The floppy drive controller has the job of turning those pulses into digital bits.) Various drive models used various combinations of read amplifiers, filtering, and a good smattering of assumptions about the incoming signal in order to send pulses at the appropriate time, These components help the drive determine if a signal is happening "too fast" and should be ignored, or "too slow" and we should turn up the amplifier because it must be missing some data. | ||
- | Many computer systems used pretty similar ways of storing data to a disk, like FM or MFM encoding, and similar media, like double density or high density. The encoding defines rules for how flux transitions should be organized on disk to represent data. The media type allows for differing densities or rates of flux transitions. Many drive manufacturers focused on these encoding standards and therefore when we ask it to read some other form of encoding, | + | Many computer systems used pretty similar ways of storing data to a disk, like FM or MFM encoding, and similar media types, like double density or high density. The encoding defines rules for how flux transitions should be organized on disk to represent data. The media type allows for differing densities or rates of flux transitions. Many drive manufacturers focused on only one of these encoding standards and therefore when we ask a drive to read some other form of encoding, |
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=== Noise === | === Noise === | ||
- | The *Noise* test in the lower left gives us a baseline for the density of noise that is generated by the drive when in "full panic" mode. Having a high noise level here **doesn' | + | The Noise test in the lower left gives us a baseline for the density of noise that is generated by the drive when in "full panic" mode. Having a high noise level here **doesn' |
=== Window Stability === | === Window Stability === | ||
- | The *Window Stability* graph at the top of the window is the analysis of what the drive can and cannot process reliably. The gray vertical lines show the results for individual tests at various flux frequencies long lines are high success rate, and short or no line means lower success rate. The gold line in the graph is a breakdown of the signal reliability along with factoring in things like spindle motor speed fluctuations and such. The most important thing you need to recognize in this graph is the durations which are covered with the gold line pinned to the top which is 100% reliability. The above graph shows that the signal is 100% stable from 3.75µs through to 19µs. If you aren't familiar with how data is stored on disks at a very low level, then that range of stability probably means absolutely nothing to you. And as an expert in this, I could give you the definitive answer of "well, it depends on what kind of disks you want to be imaging" | + | The Window Stability graph at the top of the window is the analysis of what the drive can and cannot process reliably. The gray vertical lines show the results for individual tests at various flux frequencies long lines are high success rate, and short or no line means lower success rate. The gold line in the graph is a breakdown of the signal reliability along with factoring in things like spindle motor speed fluctuations and such. The most important thing you need to recognize in this graph is the durations which are covered with the gold line pinned to the top which is 100% reliability. The above graph shows that the signal is 100% stable from 3.75µs through to 19µs. If you aren't familiar with how data is stored on disks at a very low level, then that range of stability probably means absolutely nothing to you. And as an expert in this, I could give you the definitive answer of "well, it depends on what kind of disks you want to be imaging" |
^ Media ^ Encoding ^ Platform ^ 100% Stability Required ^ | ^ Media ^ Encoding ^ Platform ^ 100% Stability Required ^ | ||
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=== First Injection Timing === | === First Injection Timing === | ||
- | The *First Injection Timing* graph is a bit more complex to explain and for the most part is irrelevant to most users. If you really want to know, there is some details about what it is showing in the last section of this page. | + | The First Injection Timing graph is a bit more complex to explain and for the most part is irrelevant to most users. If you really want to know, there is some details about what it is showing in the last section of this page. |
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The primary analog test uses a test track that is comprised of a whole bunch of smaller tests. A test has a header, gap, payload, and settle field. The header contains information about the specific test (like the gap size). Following that is the gap (no flux area) whose duration ranges from 1µs to 48µs in 250ns increments. Then there is a payload which is a special bit sequence that is used to be able to detect bit slip, desynchronization, | The primary analog test uses a test track that is comprised of a whole bunch of smaller tests. A test has a header, gap, payload, and settle field. The header contains information about the specific test (like the gap size). Following that is the gap (no flux area) whose duration ranges from 1µs to 48µs in 250ns increments. Then there is a payload which is a special bit sequence that is used to be able to detect bit slip, desynchronization, | ||
- | What it is checking for is the integrity of the gap and payload. If the gap is clean (no bits injected) and the payload is as well, then that is a success and it adds to the gray lines in the Stability graph. In the case of a failure, the payload is checked for integrity and if the payload is intact, then we check the gap. If the gap has a spurious transition (injected bit), then the time offset from the last flux transition of the header to the first spurious transition is recorded onto the First Injection Timing graph at the bottom. | + | To create the test track, the track is wiped (WRREQ on to engage head erase coil and writing no data), then the tests are generated and written. |
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+ | The test track is then read 50-ish times. |