eeprom window displays question marks

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I am developing a tiny4313 project, using Studio 7.0.1645. I have been working on this project for a while now, using an AVR Dragon as my debug interface.

Yesterday, I wanted to examine the eeprom values I store as part of my program, and to my surprise, the eeprom memory window shows the 256 bytes of eeprom locations as ????????????? instead of actual data, even the areas that have never been programmed. At address 0x0186 (which is outside the internal eeprom by a wide margin) the display reverts a series of 'ff' which is, I assume normal for unprogrammed eeprom.

This is a new phenomenon - I'm using the same device, the same debugger, the same Studio 7 app. Other memory (flash, IRAM, registers) display normally.

If I do a chip erase and read the eeprom into a hex file (using the AVR Dragon as ISP), the eeprom reads back all 0xff for the entire memory, but will show question marks once I start the debugger.

I am stumped at this point, as this is new. Also, FWIW, this happens on two different computers running the same S7 version, so I am reasonably sure it is not peculiar to one particular application install. That leaves either the device on the board (I may be able to try another one - I have to see what I have available) or the AVR Dragon, but the Dragon seems to work properly in all other aspects.

Any clues?

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Well, here's more "whaaaat??"

If I scroll through the eeprom window, at 0x0200 there are eeprom data that are correct - also at 0x0300, 0x0400, 0x0500... and so on, up to 0xff00. For some reason, 0x0000 and 0x0100 do not have this. Does this provide any additional clue as to what might be happening? As long as the data at 0x0200 looks correct, I can use it for debugging, I suppose, but I'd sure like to know why this behavior occurs.

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Is this one of these new AVRs where EEPROM maps into the single linear address space?

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clawson wrote:

Is this one of these new AVRs where EEPROM maps into the single linear address space?

I'm not sure what you mean by this, the datasheet for the ATtiny4313 shows program flash as a separate memory space, internal RAM, registers, and I/O registers as a separate SRAM memory space, and eeprom as it's own memory space.

From the data sheet:

" ATtiny2313A/4313 contains 128 bytes of non-volatile data memory. This EEPROM is organized
as a separate data space, in which single bytes can be read and written. All access registers are
located in the I/O space."

Note that the actual data are in a separate memory space, whereas the eeprom access registers are in I/O space (SRAM).

Last Edited: Fri. Oct 5, 2018 - 10:03 PM