I'm trying to extract data from 3.5" floppy disks formatted on a +D interface for a ZX spectrum. It's close but not exactly the same as for a PC. I've written software to do this in the past useing the BIOS to access a floppy.
However some disks are old and have bad sectors. I am trying to create a floppy drive controller to read a disk at a bit level to recover as much data as possible. I'm fully aware of how difficult this might be. I have however written a disk utility program that interfaced with the interface at a machine code level on the original spectrum computer, written in Z80 assembly software to emulate MSDOS to access and write files to FAT12 floppy disks. The original computer that accessed these disks did so using a 3.4MHz processor, so the Rasperry Pi that I'm thinking of using should be more than fast enough. I might even be able to run it from Linux but if not I have figured out to access the GPIO port, screen, keyboard and SD card using assembly language that would not need any kernal to run it. I've read up on how floppy drive reads and write data and have seen some basic example of how to opperate the floppy disk (not just the stepping motor).
I've done some research but have a few questions I can't seem to find answers to, and wonder if people here might know.
1) The read data pin (30). Does this return a logic high/low value of what's under the read head (rounding up or down to logic high or low), or is it analog? I ask because if it's analog, getting any input back would enable me to better try and recover corrupt sectors,but would make interface circuit harder to make, and depending on ADC used make interface with GPIO harder, and slower.
2) I know the molex power of +5V and +12V. But what current would a floppy expect?
3) I assume that the control pins from the ribbon cable on the floppy work at 0 or +5V, but that people seem to be able to run them at +3.3V. Does anyone know what they should be running at, and what their current tolerance are: what voltage and current the inputs expect, and what current/voltage the outputs deliver?
Many thanks for any information/knowledge that you might have on this.
A little late, but if someone else is interested:
1) The data output of the floppy is open-collector. So you can pull it up to your 3.3 Volts and will be fine.
2) 600 mA # 12V, 500 mA # 5V should be safe
3) Think of TTL input, that expects 2.4 Volts for HIGH. (2.5V according to the NEC 3.5" floppy drive).
Related
In one of my technical interviews I was asked one question on the subject operating system.
Question-> We have two computers.
1st computer is old with less RAM, less ROM, less processing power.
2nd computer is new computer with more RAM, more ROM and more processing power.
Let's suppose all the processes in both the computers have been stopped and only one program is run on both the computers whose time complexity is O(n).
Is it possible that initially for a short time the slow computer will process the program at a faster speed than the fast computer and only after that the fast computer will show it's real speed. If yes then tell the reason.
I was not able to tell the answer. Plz help!
You could make up lots of silly reasons why the fast machine could be behind initially, like a program that allocates and initializes as much memory as is available. So it has more startup overhead, if the RAM ratio is greater than the bandwidth ratio.
Or maybe the faster computer is a Transmeta Crusoe, or a virtual x86 emulated by Rosetta-2 on an Apple M1, and the program's machine code has to get translated to native before it can run. Dynamic translation that works like an optimizing compiler (or a JVM's JIT) takes some time at first to make efficient code, instead of just starting interpreting at best speed.
I'm confused.
I have recently started working on building an operating system while using bochs as an emulator and a certain manual online.
In the manual to move the vga framebuffer cursor I'm using the IO ports using the command 'out'. I get how to control it but I don't know what is it that I'm controlling, and after some reading it seems like everywhere it was addressed as an abstract thing that for example makes the cursor to change its position on the screen.
What I want to know: what are they physically? are they cables? if yes from where to where they are connected? can I input from them also as there name suggest? and why do I need the out command and cant write directly to their place in the memory?
If in your answer you can also include the serial ports and the difference between them and the IO ones it will be amazing,
with respect,
revolution
(btw the operating system is 32 bits)
An IO port is basically memory on the motherboard that you can write/read. The motherboard makes some memory available other than RAM. The CPU has a control bus which allows it to "tell" the motherboard that what it outputs on the data bus is to be written somewhere else than RAM. When you output to the VGA buffer, you write to video memory on the motherboard. The out/in instructions are used to write/read IO ports instead of writing to RAM. When you use out/in instructions, you instruct the CPU to set a certain line on its control bus to tell the motherboard to write/read a certain byte to an IO port instead of RAM.
Today, a lot of RAM memory is used for hardware mapping instead of IO ports. This is often called the PCI hole. It is memory mapped IO. So you will write to RAM and it will send the data to hardware like graphics memory. All of this is transparent to OS developers. You are simply using very abstract hardware interfaces which are either conventional (open source) or proprietary.
Serial ports in the meantime are simply ports which are serial in nature. A serial port is defined to be a port where data is transferred one bit at a time. USB is serial (universal serial bus). VGA is serial and others are too. These ports are not like IO ports. You can output to them indirectly using IO ports.
IO ports offer various hardware interfaces which allow to drive hardware. For example, if you have a VGA compatible screen and set text mode, the motherboard will make certain IO ports available and, when you write to these IO ports, video memory will vary depending on what you output to these ports. Eventually, the VGA screen will refresh when the video controller will output data written to video memory through the actual VGA port. I'm not totally aware of how all of this works since I'm not an electrical engineer and I never read about this stuff. To what I know, you can see the pins of the VGA port and what they do independently on wikipedia. VGA works with RGBHV. RGB stands for red, green and blue while HV stand for horizontal/vertical sync. As stated on wiki in the article on analog television:
Synchronizing pulses added to the video signal at the end of every scan line and video frame ensure that the sweep oscillators in the receiver remain locked in step with the transmitted signal so that the image can be reconstructed on the receiver screen. A sync separator circuit detects the sync voltage levels and sorts the pulses into horizontal and vertical sync.
The horizontal synchronization pulse (horizontal sync, or HSync), separates the scan lines. The horizontal sync signal is a single short pulse which indicates the start of every line. The rest of the scan line follows, with the signal ranging from 0.3 V (black) to 1 V (white), until the next horizontal or vertical synchronization pulse.
Memory in itself takes various forms in hardware. Video memory is often called VRAM (Video RAM) or the Frame Buffer as you can read in a Wikipedia article. So in itself video memory is an array of DRAM. DRAM today is one capacitor (which stores the data) and one mosfet transistor (which controls the flow of the data). So you have special wiring on the motherboard between the data bus of the processor and the VRAM. When you output data to video memory, you write to VRAM on the motherboard. Where you write and how just depends on the video mode you set up.
Most modern systems work with HDMI/Display port along with graphics card. These graphics card are other hardware interfaces which are often complex and they often cannot be known because the drivers for the cards are provided by the manufacturers. osdev.org has information on Intel HD Graphics which has a special interface to interact with. It can be used to gather info on the monitor and to determine what RAM address to use to write to the monitor.
So I am currently learning Operating Systems and Programming.
I want how the registers work in detail.
All I know is there is the main memory and our CPU which takes address and instruction from the main memory by the help of the address bus.
And also there is something MCC (Memory Controller Chip which helps in fetching the memory location from RAM.)
On the internet, it shows register is temporary storage and data can be accessed faster than ram for registers.
But I want to really understand the deep-down process on how they work. As they are also of 32 bits and 16 bits something like that. I am really confused.!!!
I'm not a native english speaker, pardon me for some perhaps incorrect terminology. Hope this will be a little bit helpful.
Why does registers exists
When user program is running on CPU, it works in a 'dynamic' sense. That is, we should store incoming source data or any intermediate data, and do specific calculation upon them. Memory devices are needed. We have a choice among flip-flop, on-chip RAM/ROM, and off-chip RAM/ROM.
The term register for programmer's model is actually a D flip-flop in the physical circuit, which is a memory device and can hold a single bit. An IC design consists of standard cell part (including the register mentioned before, and and/or/etc. gates) and hard macro (like SRAM). As the technology node advances, the standard cells' delay are getting smaller and smaller. Auto Place-n-Route tool will place the register and the related surrounding logic nearby, to make sure the logic can run at the specified 3.0/4.0GHz speed target. For some practical reasons (which I'm not quite sure because I don't do layout), we tend to place hard macros around, leading to much longer metal wire. This plus SRAM's own characteristics, on-chip SRAM is normally slower than D flip-flop. If the memory device is off the chip, say an external Flash chip or KGD (known good die), it will be further slower since the signals should traverse through 2 more IO devices which have much larger delay.
how they work together with cpu
Each register is assigned a different 'address' (which maybe not open to programmer). That is implemented by adding address decode logic. For instance, when CPU is going to execute an instruction mov R1, 0x12, the address decode logic sees the binary code of R1, and selects only those flip-flops corresponding to R1. Then data 0x12 is stored (written) into those flip-flops. Same for read process.
Regarding "they are also of 32 bits and 16 bits something like that", the bit width is not a problem. Both flip-flops and a word in RAM can have a bit width of N, as long as the same address can select N flip-flops or N bits in RAM at one time.
Registers are small memories which resides inside the processor (what you called CPU). Their role is to hold the operands for fast processor calculations and to store the results. A register is usually designated by a name (AL, BX, ECX, RDX, cr3, RIP, R0, R8, R15, etc.) and has a size which is the number of bits it can store (4, 8, 16, 32, 64, 128 bits). Other registers have special meanings, and their bits control the state or provide information about the state of the processor.
There are not many registers (because they are very expensive). All of them have a capacity of only a few kilobytes, so they can't store all the code and data of your program, which can go up to gigabytes. This is the role of the central memory (what you call RAM). This big memory can hold gigabytes of data and each byte has its address. However, it only holds data when the computer is turned on. The RAM reside outside of the CPU Chip and interacts with him via Memory Controller Chip which stands as interface between CPU and RAM.
On top of that, there is the hard drive that stores your data when you turn off your computer.
That is a very simple view to get you started.
Looking for some help to be honest, This is not my area of knoladge atall.
Ive read around the question of powering my Pi with a battery, now I nabbed one of these guys for my phone
http://www.amazon.co.uk/13000mAh-Portable-External-Technology-Motorola-Black/dp/B00BQ5KHJW/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1420826597&sr=1-1-catcorr&keywords=anker+astro+e4
Incase the link dies in the future;
Item model number: AK-79AN13K2-BA
Anker® 2nd Gen Astro E4 13000mAh 2-Port (3A Output) Fast
Max 3A Out
5V Out
Now, from what i've read there have been mixed notes of, don't use batterys, only use this battery, don't do this, don't exeed this magical number ( which was differant each time ). so any help would be grately needed. If i was to power my pi via this thing. im I going to get a poof of smoke and need to replace the poor pi :(
A raspberry Pi is powered via USB, which means that it simply takes the 5V supplied via USB to run. As long as your current source is stable (ie. it doesn't change when you draw current from it), no device will care whether it is a battery or a switching power supply. Now, a bare raspberry Pi B uses less than 2W of power, 2W/5V = 0.4A = 400mA, so if that battery pack lives up to its specification, you are going to be fine. The device is spec'ed to provide 13000mAh, so at a constant current of 400mA, this would last you more than 32 hours.
Now, most people attach something to the raspberry, and that something will also draw power, but just add that power to the calculations above, to see if it's going to work out.
Considering that a processor runs at 100 MHz and the data is coming to the processor from an external device/peripheral at the rate of 1000 Mbit/s (8 Bits/Clockcycle # 125 MHz), which is the best way to handle traffic that comes at a higher speed to the processor ?
First off, you can't do it in software. There would be no way to sample the digital lines at a sufficient rate, or to doing anything useful with it.
You need to use a hardware FIFO buffer or memory cell. When a data burst comes in, it can be buffered in the high speed FIFO and then read out as needed by the processor.
Drop in high speed FIFO chips are surprisingly expensive (though most are dual ported). To cut cost, you would be best off using an SRAM chip, and a hardware adder to increment the address lines on incoming data.
This is not an uncommon situation for software. semaj said the right word. This is a system engineering issue. Other folks have the right answer too. If you want to look at or process that data with the 100MHz processor, it is not going to happen, dont bother trying. You CAN look at snapshots of it or have the hardware filter out a specific percentage of it that you are looking for. At the end of the day though it is a systems issue, what does the hardware provide, where does it put this data, what is the softwares task for this data, does it see X buffers of data come in on the goesinta, and the notify the goesouta hardware that there are X buffers ready to go? Does the hardware examine and align the buffers so that you can look at a header, and then decide where to route the hardware? Once you do your system engineering you will know if you can use that processor or not, and if you can use it what its job is and how to do it.
Your direct question. What is the best way to handle it. The best way to handle it is to have hardware (fpga, asic, etc) move it into and out of some storage device (ram of some sort probably). Not necessarily the same ram the processor runs out of (DMA is a good thing to avoid). The hardware is something the software can talk to but you cannot examine all of that data so dont try. Without knowing what kind of data this is, what form, what the software looks at how much work you are willing to force the hardware to do, etc determines the rest of the answer. If you expect a certain (guaranteed) percentage to be bad or not belong to this processor, etc have the hardware filter that out and then what is left you can process.
Networking is a good example of this, PCs have gige ports but cannot process GigE line rate data. That is why we use switches now instead of hubs, hardware slices out a percentage of the data so the pc can handle it, the protocols take care of the data that cannot be processed by resending it later. And the switches processors dont look at all of the data, the hardware slices it up so the software can examine just the header. Or sometimes the software simply manages tables that drive the hardware and the hardware does all the work of processing the data.
Do your system engineering the answers will simply fall out.
You buffer it. Typically data from a device is written to a memory buffer (circular queue) using DMA (no cpu involved). The cpu reads from the memory buffer at a constant rate. Usually devices send data in bursts. This keeps the buffer from filling up. If there is too much data, buffer overflow.
DMA (direct memory access) is possibly the solution, however, it seems unlikely that the memory bus could run faster than the processor core, so the receiving peripheral would have to accept data into a larger register than 8 bit because 125MHz could not be sustained. For example a 16bit register would allow memory writes at 62.5MHz which may be achievable. Also the receiving device would have to be able to accept an external clock that is both faster and asynchronous to the core clock. Also of course the receiving peripheral must have support for DMA.
Unless you are more specific about your hardware and the communication protocol it is difficult to give anything other than a general answer.