hw-remap/pause-arm/ref (libmmu.la :: mmu_component_library)


The remap and pause controller, present on the ARM PID7T board, handles four rather independent functions:



The controller has a variety of functions, most of which are trivial to simulate. A minimal implementation is provided for controller identification. The most complex aspect of this component is how remapping is handled. During boot-up, the controller uses a "reset map" that maps a range of addresses to some other location (typically address 0). At some point, the target program will write to one of the controller's registers, causing it to switch to a "normal map", in which case no address translation occurs.

In order for the mapping to occur, this controller must be placed between the CPU and other components, such as peripherals and the main memory. This additional level of indirection for bus traffic (particularly between a CPU and memory) may introduce performance penalties. This controller should be used only when necessary. Even then, it is possible to route bus traffic around this component if the remapping facility is not required.

register access

The registers bus provides read/write access to the internal registers of the remap/pause controller. The memory map of the register set is shown below. More detail about each of these registers can be found in the ARM documentation (see ``References'').

address read write
0 (reserved) pause
+ 0x10 identification (reserved)
+ 0x20 (reserved) clear reset map
+ 0x30 reset status reset status set
+ 0x34 (reserved) reset status clear

If the reset pin is driven with a non-zero value, the reset status is updated within the component such that interrogating the controller's reset status will indicate that a power on reset has occurred.


The halt! pin may be connected to a component such as an ARM CPU which knows to halt instruction processing when the pin is driven with a non-zero value. This pin will be driven when the pause register is written to.


This access-port bus provides upstream access the remapper function in this component. Reads/writes to this bus are translated (if appropriate) and passed onto the second bus, as set by the all accessor.

remapping setup

The remapping? attribute specifies which memory map will be used. It is anticipated that this attribute will be used at the start of a simulation session to provide the equivalent of a jumper for enabling the reset or the normal memory map at power-up. If the attribute is set to `yes', then any relocations that have been defined will apply. As usual, writing to the `clear reset map' register will cause the normal map to be used.

Please note that the polarity of the remapping? flag is opposite to some ARM documentation. ARM refers to a "Normal (Remapped)" condition on the PID7T board when the customary sid mapping is disabled, and "Reset" mapping condition when the customary sid mapping is enabled. This is just a terminology and sid configuration policy issue.

The num-relocations attribute specifies how many relocations are to be defined via the numeric N- attributes (see below). This serves little purpose other than to dynamically generate the N- attributes necessary for defining the relocations. Note: this attribute may only be set once.

The N-start family of attributes specify the starting addresses of a memory regions that are to be relocated to a different location. If there are three available relocations (due to setting num-relocations to 3), then there will be three sets of attributes, prefixed by 0-, 1-, and 2-. The first starting address attribute is 0-start.

The N-end family of attributes specify the end of the memory regions that are to be relocated to a different location. Usually, this is: (base + limit) - 1 That is, the address given to the N-start and N-end attributes are all inclusive.

The N-reloc-to family of attributes specify the addresses to which region N will be relocated.

SID Conventions
functional supported -
save/restore supported -
triggerpoints supported

It provides a single attribute-based triggerpoint, remapping?.


Related components

Component Reference:

Component: hw-remap/pause-arm/ref

resetin0 or non-zeroresetting
halt!out0 or non-zerohalting

access-portall addressesanyremapping
registers0x0 to 0x37read/write wordsregister access

namecategorylegal valuesdefault valuebehaviors
remapping?settingboolean stringtrueremapping, remapping setup
num-relocations-numeric string0remapping setup
N-startsettingnumeric string-remapping setup
N-endsettingnumeric string-remapping setup
N-reloc-tosettingnumeric string-remapping setup

allany bus operationremapping


More details about this controller can be found on the web.