Is there a way to find out the instruction format (R/I/S/B/U/J) from the opcode field [6:0] of the instruction? I searched the ISA manual but couldn't find it. That is quite important to decode the instruction, or did I miss something essential?
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I've wondered this for a while. Why can't you just take a binary ROM of for example a NES or N64 ROM, and just convert the executable parts from MIPS or 6502 to x86 assembly? I mean all the opcodes are covered anyway.
I know theres a handful of ARM codes that can't be converted over, but for consoles up until the WII, couldn't one just convert the assembly code and intercept IO stuff like rendering and gamepad input?
Because it feels like that would speed up emulation considerably.
I want compare 32bit reg with rom 1024x32 .
best way for this search?
vhdl code
Sounds like you want a content-addressable memory (CAM).
The basic idea is that a CAM can be searched for values (32-bit word) to get keys (addresses). It does this by having a list of valid addresses per 32-bit word stored in some local memory.
Check out this application note by Xilinx for a more technical description.
I tried to use Digital Clock Manager (DCM) and double the input clock. iSim (Xilinx simulation tool) gives the correct result, but in Modelsim the output clock is always zero.
I always compile the unisims folder (that consist of IBUFG, DCM and BUFG modules in xilinx software) in the library of my project in modelsim.
According to the Russel Answer I used Xilinx Core Generator. I want the frequency of CLKFX to be double of CLKIN. As you see in the following pictures, the results of iSim (Xilinx simulator) is correct, but in Modelsim CLKFX is always zero :
iSim results (Xilinx Simulator) :
Modelsim results :
If you think you're not setting up the DCM correctly, you need to read the documentation about DCMs and how they work. If you search for Xilinx Library Guide (+FPGA Name) you'll find all of the Primitives that are available in your device. Or you can look at the full list here:
Xilinx Library Guides
If you're still having trouble after looking at all of your parameters, you can try using CoreGen to generate your DCM for you. CoreGen will ensure that you do not make any mistakes or instantiate something in an invalid configuration. The output of CoreGen is a .vhd file that you can drop into your modelsim project and simulate with that.
I.e. are the different addressing modes encoded somehow in the opcodes? Can they be extracted programmatically or does this info only exist in the documentation of the 6502? I'm writing an emulator and I'm not concerned with performance. It would be nice to have a function that takes an opcode and returns the addressing mode, if possible.
So far I've not come across any indication that there's a pattern in the codes, except that all zero page instructions seem to have their third bit set.
Yes there is. The addressing mode is encoded in 3 bits at positions 4-2 in the opcode byte (i.e. xxxAAAxx). Decoding the addressing mode is dependent on the other bits, but they conform to a regular pattern (mostly) which can be dropped through a lookup table to determine the mode for each instruction type.
This page has a full description of the various patterns and how to decode in each case.
I have searched for Addressing modes in IA-32,but I haven't seen any website or an article which have explained the addressing modes simply.
I need an article or something which explain the matter simply by some picture of the memory during it changes and specifying the address mode by pictures.
I know that in IA-32 general form of addressing follows the following form :
Segment + Base + (index * scale) + displacement
I want to know the exact meaning of the displacement,scale,index and finally the base.
As I don't know English as well I forced to search them but I didn’t find the technical mean of the words for this case ( In assembly programming language I mean ).
Finally, I want an explanation of addressing modes in IA-32 simply and preferably have been represented by pictures about The memory and its offset and ...
I learn assembly programming language by A guide to assembly programming in Linux's book.
So thanks.
Found this image from this power point presentation.
This means that you can have addresses like [eax + ecx * 2 + 100]. You don't necessarily have to use all of these fields.
See also Referencing the contents of a memory location. (x86 addressing modes)
The scale factor is encoded into machine code as a 2-bit shift count. ESP can't be an index because of special cases for indicating the presence of a SIB byte and for a SIB byte with no index. See rbp not allowed as SIB base? for a rundown on the special cases.
Segmentation can be ignored in 32/64-bit mode under normal OSes like Linux.
The segment register is selected automatically depending on the base register in the addressing mode, or with segment override prefix (e.g. ds:, cs:).
But Linux uses a flat memory model so the segment base is always 0 for all segments (other than fs or gs, used for thread-local storage). The segment base is added to the "offset" calculated from base, index, scale and displacement to get the final linear address. So normally the "offset" part is the whole linear address.
That linear address is a virtual address, which the hardware translates to physical via the page tables / TLB (managed by the kernel).