Msg/MemoryNoDevice - Revision history

Henry at 05:51, 11 March 2019

2019-03-11T05:51:31Z

← Older revision		Revision as of 05:51, 11 March 2019
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	The computer system has a 32-bit address space (addresses are 32 bits, and there is 2<sup>32</sup> bytes = 4 gigabytes of address space), but usually only part of that space actually contains memory or I/O devices. This message tells you that a memory access tried to access a location within the address space that is not used by any memory or I/O devices.		The computer system has a 32-bit address space (addresses are 32 bits, and there is 2<sup>32</sup> bytes = 4 gigabytes of address space), but usually only part of that space actually contains memory or I/O devices. This message tells you that a memory access (or instruction fetch) tried to access a location within the address space that is not used by any memory or I/O devices.

	=== Examples ===		=== Examples ===
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	ldr r0, =0xe0000000 // Somewhere outside memory and I/O devices.		ldr r0, =0xe0000000 // Somewhere outside memory and I/O devices.
	ldr r1, [r0] // Where is this reading from? Nothing.		ldr r1, [r0] // Where is this reading from? Nothing.

			bx r0 // Branch to nowhere
	</syntaxhighlight>		</syntaxhighlight>
	==== Nios II ====		==== Nios II ====
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	movia r2, 0xe0000000 # Somewhere outside memory and I/O devices.		movia r2, 0xe0000000 # Somewhere outside memory and I/O devices.
	ldw r3, 0(r2) # Where is this reading from? Nothing.		ldw r3, 0(r2) # Where is this reading from? Nothing.

			jmp r2 # Branch to nowhere
	</syntaxhighlight>		</syntaxhighlight>

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	=== Debugging ===		=== Debugging ===
	* Check the address used for the memory access.		* Check the address used for the memory access.
			* For instruction fetches, it means that the PC value is very incorrect. This is often caused by a branch with an incorrect target address. To find the offending branch, try using the [https://cpulator.01xz.net/doc/#callstack <b>Trace window</b>] (located in the same panel as the registers window by default) to look backwards in the program execution.

	=== Implementation ===		=== Implementation ===
	For every memory access, the simulator needs to find the memory or I/O device that services the address used by the request, and complains if none is found. This warning is generated while executing the load or ~~store~~.		For every memory access (including instruction fetches), the simulator needs to find the memory or I/O device that services the address used by the request, and complains if none is found. This warning is generated while executing the load, store, or instruction fetch.

	{{DisableMsg\|Memory access out of range}}		{{DisableMsg\|Memory access out of range}}

Henry at 05:35, 11 March 2019

2019-03-11T05:35:28Z

← Older revision		Revision as of 05:35, 11 March 2019
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	</syntaxhighlight>		</syntaxhighlight>

	Note that these examples assume you're using a computer system other than the ~~base~~ "~~4GB memory~~" systems, which have memory mapped to the entire 32-bit address space, ~~so does not actually have any~~ addresses that ~~aren't~~ mapped to ~~something~~.		Note that these examples assume you're using a computer system other than the "generic" systems, which have 4 GB memory mapped to the entire 32-bit address space. Since there is memory mapped to the entire address space, there are no addresses that are mapped to nothing.

	=== Debugging ===		=== Debugging ===

Henry: Created page with "The computer system has a 32-bit address space (addresses are 32 bits, and there is 2³² bytes = 4 gigabytes of address space), but usually only part of that space a..."

2019-03-11T05:33:16Z

Created page with "The computer system has a 32-bit address space (addresses are 32 bits, and there is 2<sup>32</sup> bytes = 4 gigabytes of address space), but usually only part of that space a..."

New page

The computer system has a 32-bit address space (addresses are 32 bits, and there is 2<sup>32</sup> bytes = 4 gigabytes of address space), but usually only part of that space actually contains memory or I/O devices. This message tells you that a memory access tried to access a location within the address space that is not used by any memory or I/O devices.

=== Examples ===
==== ARMv7 ====
<syntaxhighlight line lang="Asm" highlight="4">
.global _start
_start:
ldr r0, =0xe0000000 // Somewhere outside memory and I/O devices.
ldr r1, [r0] // Where is this reading from? Nothing.
</syntaxhighlight>
==== Nios II ====
<syntaxhighlight line lang="Asm" highlight="4">
.global _start
_start:
movia r2, 0xe0000000 # Somewhere outside memory and I/O devices.
ldw r3, 0(r2) # Where is this reading from? Nothing.
</syntaxhighlight>

Note that these examples assume you're using a computer system other than the base "4GB memory" systems, which have memory mapped to the entire 32-bit address space, so does not actually have any addresses that aren't mapped to something.

=== Debugging ===
* Check the address used for the memory access.

=== Implementation ===
For every memory access, the simulator needs to find the memory or I/O device that services the address used by the request, and complains if none is found. This warning is generated while executing the load or store.

{{DisableMsg|Memory access out of range}}

Msg/MemoryNoDevice - Revision history

Henry at 05:51, 11 March 2019

Henry at 05:35, 11 March 2019

Henry: Created page with "The computer system has a 32-bit address space (addresses are 32 bits, and there is 232 bytes = 4 gigabytes of address space), but usually only part of that space a..."

Henry: Created page with "The computer system has a 32-bit address space (addresses are 32 bits, and there is 2³² bytes = 4 gigabytes of address space), but usually only part of that space a..."