= GIET_VM / Mapping =

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The GIET_VM is a fully '''static operating system''' for shared address space, many-cores architectures. These architecture are generally  NUMA (Non Uniform memory Acces), because the memory is logically shared, but physically distributed, and the main goal of the GIET_VM is to address these NUMA issues. 

the GIET_VM bootloader map the kernel and one or several multi-threaded user applications on the target architecture. 
All software objects (user applications code and data, but also kernel code and critical kernel structures such as the page tables or the processors schedulers) are statically build and loaded from disk into physical memory by the GIET_VM bootloader in the boot phase. 

The main advantage of this static approach is to provide the system designer to place the tasks on the processors, but also to place software objects on the distributed physical memory banks. It supports replication of (read-only) critical objects such as kernel code, user code, or page tables. The page tables are statically initialised in the boot phase, and are not modified anymore in the execution phase.

To define the mapping, the system designer must provide a '''map.bin''' file containing a dedicated C binary data structure, that is loaded in memory by the bootloader.

The next section describes this C binary structure. The following sections describe how  this binary file can be generated by the '''genmap''' tool from a python language description. Finally the genmap tool can generate a readable '''map.xml''' representation of the '''map.bin''' file.

== __C mapping data structure__ ==

The C mapping data structure contains the following informations:

 1.  It contains a description of the target, clusterized, hardware architecture, with the following constraints: Processor cores are MIP32. The clusters are organised in a 2D mesh topology, and the number of clusters is variable (can be one). The number of processors per cluster is variable (can be one). The number of  physical memory banks is variable (up to one physical memory bank per cluster. Most peripherals are ''external'' and  localized in one specific I/O cluster. The physical address width is between 32 and 48 bits, and is the concatenation of 3 fields: the LSB field (32 bits) define a 4 Gbits physical address space inside a single cluster. The X  and Y  fields (up to 8 bits for each field) define the cluster coordinate.

 2. It contains a description of the user applications to be launched on the platform. An user application is characterized by a a virtual address space, called a ''vspace''. An user application can be multi-threaded, and the number of parallel tasks sharing the same address space in a given application is variable (can be one). The GIET_VM provide a specific Multi-Writer/Multi-Reader communication middleware for send/receive inter-tasks communication. Each vspace contains a variable number of virtual segments, called ''vsegs''. The number of simultaneously mapped vspaces on a given architecture is variable (can be one).

 3. It contains the mapping directives: The tasks are statically allocated to processors. The various software objects (user and kernel code segments, tasks stacks, tasks heaps, communication channels, etc.) are called ''vobjs'', and are statically placed on the distributed physical memory banks (called ''psegs''),  using the page tables (one page table per vspace) that define the mapping of the vsegs on the psegs.

The C binary mapping data structure is defined in the [source:soft/giet_vm/giet_xml/mapping_info.h mapping_info.h] file, and is organised as the concatenation of a fixed size header, and 11 variable size arrays:
|| mapping_cluster_t    || a cluster                 || contains psegs, processors, peripherals and coprocessors ||
||  mapping_pseg_t      || a physical segment ||                                                                                          ||  
||  mapping_vspace_t   || a virtual space        || contains several vsegs and several parallel tasks                ||
||  mapping_vseg_t      || a virtual segment    || contains one or several vobjs                                             ||     
||  mapping_vobj_t       || a software object    ||                                                                                          ||
||  mapping_task_t       || a task                      ||                                                                                         ||  
||  mapping_proc_t       || a processor             ||                                                                                         ||
||  mapping_periph_t   ||  a peripheral            || can contain IRQ inputs (XCU or PIC)                                  ||
||  mapping_irq_t         || a source interrupt   ||                                                                                          || 
||  mapping_coproc_t   || a coprocessor          || contains several cp_ports                                                 || 
||  mapping_cp_port_t  || a coprocessor port  ||                                                                                         ||

The ''map.bin'' file must be stored on disk and will be loaded  in memory by the GIET_VM bootloader in the ''seg_boot_mapping'' segment. 

== __Python mapping description__ ==

A specific mapping requires at least two python files:
 * The '''arch.py''' file is attached to a given hardware architecture. It describes both the (possibly generic) hardware architectures, and the mapping of the kernel software objects on this hardware architecture.
 * The '''appli.py''' file is attached to a given user application. It describes both the application structure (tasks and communication channels), and the mapping of the application tasks and software objects on the architecture.

The various Python Classes used by these these files are defined in the [source:soft/giet_vm/giet_python/mapping.py mapping.py] file.

== __Python hardware architecture description__ ==

The target hardware architecture must be defined in the ''arch.py'' file , you must use the following constructors:

=== 1. mapping ===

The Mapping( ) constructor build a mapping object and define the target architecture general parameters:

|| name               || mapping name == architecture name ||
|| x_size              || number of clusters in a row of the 2D mesh ||
|| y_size              || number of clusters in a column of the 2D mesh ||              
|| nprocs             || max number of processors per cluster ||     
|| x_width           || number of bits to encode X coordinate in paddr  ||
|| y_width            || number of bits to encode Y coordinate in paddr  ||
|| p_width            || number of bits to encode local processor index  ||
|| paddr_width     ||  number of bits in physical address ||
|| coherence        || Boolean true if hardware cache coherence ||      
|| irq_per_proc     || number of IRQ lines between XCU and one proc (GIET_VM use only one) || 
|| use_ramdisk     || Boolean true if the architecture contains a RamDisk ||
|| x_io                  || io_cluster X coordinate ||         
|| y_io                  || io_cluster Y coordinate ||
|| peri_increment || virtual address increment for peripherals replicated in all clusters ||
|| reset_address   || physical base address of the ROM containing the preloader code ||
|| ram_base          ||physical memory bank base address in cluster [0,0] ||
|| ram_size          || physical memory bank size in one cluster (bytes) ||

=== 2. Processor core ===

The '''mapping.addProc( )''' construct define one MIPS32 processor core in a cluster (number of processor cores can different in different clusters). It has the following arguments:
|| x      || cluster x coordinate ||
|| y      || physical ||
|| p      || physical memory bank size (bytes) ||

The physical global processor index will be : ( ( x << y_width ) + y ) << p_width ) + p

=== 3. Physical memory bank ===

The '''mapping.addRam( )''' construct define one physical memory bank, and the associated physical segment in a cluster. It has the following arguments:
|| name      || segment name ||
|| base       || physical memory bank base address ||
|| size        || physical memory bank size (bytes) ||

The target cluster coordinates (x,y) is defined by the base address MSB bits.

=== 4. Physical peripheral ===

The '''mapping.addPeriph( )''' construct adds one peripheral, and the associated physical segment in a cluster. It has the following arguments:
|| name      || segment name ||
|| base       || peripheral segment physical base address ||
|| size        || peripheral segment size (bytes) ||
|| ptype     || Peripheral type ||
|| subtype  || Peripheral subtype ||
|| channels || number of channels for multi-channels peripherals ||
|| arg          || optionnal argument depending on peripheral type ||

The target cluster coordinates (x,y) is defined by the base address MSB bits.
The supported peripheral types and subtypes are defined in the [source:soft/giet_vm/giet_python/mapping.py mapping.py] file.

=== 5. Interrupt line ===

The '''mapping.addIrq()''' construct adds one IRQ line input to an XCU peripheral, or to a PIC peripheral. It has the following arguments:
|| periph   || peripheral receiving the IRQ line ||
|| index    || input port index ||
|| isrtype  || Interrupt Service Routine type ||
|| channel || channel index for multi-channel ISR ||

The supported ISR types are defined in the [source:soft/giet_vm/giet_python/mapping.py mapping.py] file.

== __Python kernel mapping__ ==

The mapping of the GIET_VM vsegs must be defined in the ''arch.py'' file.

Each kernel virtual segment has the ''global'' attribute, and must be mapped in all vspaces. It can be mapped to a set of consecutive small pages (4 Kbytes), or to a set of consecutives big pages (2 Mbytes). 

The '''mapping.addGlobal()''' construct define the mapping for one kernel vseg. It has the following arguments:
|| name       || virtual segment name  ||
|| vbase       || virtual base address ||
|| size          || segment size (bytes ||
|| mode        || access rights (CXWU) ||
|| vtype        || vseg type  ||
|| x              || destination cluster X coordinate ||
|| y              || destination cluster Y coordinate ||
|| pseg        || destination pseg name ||
|| identity    || identity mapping required (default = False) ||
|| binpath    || pathname for binary file if required (default = ' ') ||
|| align        || alignment constraint if required (default = 0) ||
|| local        || only mapped in local page table if true (default = False) ||
|| big          || to be mapped in big pages (default = False) || 

The supported values for the ''mode'' argument, and for the ''vtype'' arguments are defined in the [source:soft/giet_vm/giet_python/mapping.py mapping.py] file.
The ''x'', ''y'', and ''pseg'' arguments define actually the mapping.

=== 1. Boot vsegs ===

There is 4 'vsegs for the GIET_VM bootloader:
 * The '''seg_boot_mapping''' vseg contains the C binary structure defining the mapping. It is loaded from disk by the boot-loader.
 * The '''seg_boot_code''' vseg contains the boot-loader code. It is loaded from disk by the preloader.
 * The '''seg_boot_data''' vseg contains the boot-loader global data.
 * The '''seg_boot_stacks''' vseg contains the stacks for all processors.
These 4 vsegs must be identity mapping (because the page table are not available), and are mapped in the first big physical page (2 Mbytes) in cluster [0][0].

=== 2. Kernel vsegs ===

There is six types of vsegs for the GIET_VM kernel, but some vsegs are replicated in all clusters, to improve locality and minimize contention, as explained below:
 * The '''seg_kernel_ptab_x_y''' vseg has type PTAB. It contains the page tables for all vspaces (one page table per vspace). There is one such vseg in each cluster (one set of page tables per cluster). Each PTAB vseg is mapped in one big physical page. 
 * The '''seg_kernel_code''' & '''seg_kernel_init''' have type ELF. They contain the kernel code. These two vsegs must be mapped in one big physical page. They are  replicated in each cluster. The ''local'' attribute must be set, because the same virtual address will be mapped on different physical address depending on the cluster.   
 * The  '''seg_kernel_data''' & '''seg_kernel_uncdata''' have type ELF. They contain the kernel global data (cacheable, or non cacheable). They are not replicated, and must be mapped in cluster[0][0]. 
 * The '''seg_kernel_sched_x_y''' vseg has type SCHED. It contains the processor schedulers (one scheduler per processor). There is one such vseg in each cluster, and it must be mapped on small pages (two small pages per scheduler).

=== 3. Peripheral vsegs ===

A global vseg must be defined for each addressable peripheral. 
As a general rule, we use big physical page(s) for each external peripheral, and one small physical page for each replicated peripheral.

== __Python user application mapping__ ==

The mapping of a given application  must be defined in the ''application.py'' file.

A vspace, containing a variable number of tasks, and a variable number of vsegs, must be defined for each application.

There is several types of user vseg  
 * The '''code''' vseg can be optionally replicated in all clusters. 
 * The '''data''' vseg is not replicated. It must contain the ''start_vector'' defining the entry points of the application tasks.
 * It must exist as many '''stack'''' vseg as the number of tasks. 
 * One or several '''heap''' vseg(s), can be used by the malloc user library.
 * One or several '''mwmr''' vseg(s)
 
=== 1. create the vspace ===

The '''mapping.addvspace( )''' construct define a vspace. It has the following arguments:
|| name        || vspace name == application name  ||
|| startname || name of              || 

===  2. vseg mapping ===

The '''mapping.addVseg( )''' construct define the mapping of a vseg in the vspace. It has the following arguments:
|| vspace     || vspace containing the vseg ||
|| name       || vseg name ||
|| vbase       || virtual base address ||
|| size         || vseg size (bytes) ||
|| mode      || access rights (CXWU) ||
|| vtype       || vseg type ||
|| x              || destination cluster X coordinate ||
|| y              || destination cluster Y coordinate ||
|| pseg        || destination pseg name ||
|| binpath    || pathname for binary file if required (default = ' ') ||
|| align        || alignment constraint if required (default = 0) ||
|| local        || only mapped in local page table if true (default = False) ||
|| big          || to be mapped in big pages (default = False) || 

The supported values for the ''mode'' argument, and for the ''vtype'' arguments are defined in the [source:soft/giet_vm/giet_python/mapping.py mapping.py] file.
The ''x'', ''y'', and ''pseg'' arguments define actually the mapping.

=== 3. task mapping ===

The '''mapping.addVseg( )''' construct  define the mapping of  a task in the vspace. It has the following arguments:
|| vspace       || vspace containing the task ||
|| name         || task name (unique in vspace) ||
|| trdid          || thread index (unique in vspace] ||
|| x                || destination cluster X coordinate ||
|| y                || destination cluster Y coordinate ||
|| lpid            || destination processor local index ||
|| stackname || name of vseg containing stack ||
|| heapname  || name of vseg containing heap ||
|| startid        || index in start vector (defining the task entry point virtual address) ||

The ''x'', ''y'', ''lpid'' arguments define actually the task placement.