nios II implementation problem

Hello nipu_n,

You are absolutely right that the on-chip ROM will lost the data after power-down the device. The data will be written into the ROM during config of the FPGA after power-on. So the configuration data holds the ROM data too.

Bye,

niosIIuser

> what's the use of on-chip ROM.

There's no write enable ... so it won't get corrupted by code

that doesn't play nice. Basically, it's useful for code/data that

must remain consistent when a device (re)configuration does not

occur (e.g. software reset/watchdog reset) ... otherwise, there's

little motivation to use on-chip ROM over on-chip RAM.

> because whenever we there is a power off, data will vanish!

Well ... this is really depends on your point-of-view I guess ... but

once the Cyclone/Stratix device is configured the on-chip ROM is

available ... if the device isn't configured ... then it really doesn't

matter ;-)

Regards,

--Scott

One other reason to select a ROM is in case you plan to move your design to Hardcopy.

Hardcopy doesn't support initialized RAMs but does support ROMs.

hi nipu_n,

in case your question is more basic:

Altera FPGAs are SRAM-based devices, other vendors provide FLASH-based FPGAs. So SRAM-FPGAs looses its content everytime power is removed. Everytime power is connected, the FPGA needs to be configured, that means loaded with your specific design. Because on-chip ROM is part of your design, it is initialized while configuring the device.

In a stand-alone application you have to add an extra FLASH-device (e.g. serial FLASH EPCSxx) which is programmed with your design and automatically loads your FPGA after power up (in milliseconds).

Mike

i have some more doubts regarding the on-chip components in NIOSII - cyclone;

*how can i store some data into on-chip ROM?

* how it is possible to count the number of LEs used by different on-chip components?

am waiting for your valuable responses......

nipu_n,

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*how can i store some data into on-chip ROM?[/b]

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How you populate them depends on your flow. I&#39;ve used both .hex and .mif formats to populate memories in Quartus II.

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* how it is possible to count the number of LEs used by different on-chip components?[/b]

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Quartus II will give you both a post-synthesis and post-compilation report summarizing the resources used. This should give you what you&#39;re looking for.

Cheers,

- slacker

One little detail about the on-chip ROM&#39;s:

Its read-only, yes but not when debugging inside nios ide. Somehow the nios IDE is able to load a new pattern into the ROM without reloading the FPGA sof file! Which means there is a write operation taking place.

Someone could maybe explain how this is done. I can only guess.

nipu_n,

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*how can i store some data into on-chip ROM?[/b]

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When you create your software with Nios II IDE and use somewhere in your programme that on-chip ROM, the compiler creates a &#39;rom-name.hex&#39; file in your fpga directory, containing the data you&#39;ve defined ( e.g. as &#39;const int rom_data[]&#39; ). SOPC-Builder now adds your data to FPGA configuration data in its next compilation step. ROM, created with &#39;MegaWizard Plug-In Manager&#39; can be initialized by using &#39;Tools->In-System Memory Content Editor&#39;

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* how it is possible to count the number of LEs used by different on-chip components?[/b]

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I don&#39;t know if there is a feature to estimate the amount of LEs, but after compiling you can see it in the hierachy window or in

&#39;Compilation Report->Fitter->Resource Section&#39;. The amount of LEs depends on your specific settings for the compilation process.

Mike

Yes, most on-chip ROMs are writable when the processor is in debug mode.

To explain - when Quartus instantiates a ROM it&#39;s normally using M4K blocks but not connecting the write enable. SOPC builder ROMs have the write enable connected, but gated by a signal which the processor outputs when in debug mode.

This is safe, as when the processor is in debug mode its running a debug monitor supplied by nios2-gdb-server. This monitor can be used to write code into the ROMs if you change it from within the IDE to save you from having to download a new SOF.

Next time you synthesise the design Quartus will pick up the most recent output from the IDE and put that into your SOF file.