If the memory View is showing "???????", it means that the addresses are unknown to GDB.
There are 2 possible cases in which this might happen
(1) There is no device, or a read error, or can not read
(2) Restricted by the memory map
For example, take a look at our default N8 memory map.
Due to not setting the region at the entered address, the memory view shows "????????"
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Please refer to the below picture, which shows how you can add new memory regions to the default memory map.
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Mem_view2.jpg [ 212.16 KiB | Viewed 44379 times ]