hw-cpu-xstormy16 (libcgencpu.la :: cgen_component_library)

Synopsis:

This component models the Sanyo Xstormy16a processor.


Functionality:

Modelling:

This component models a Xstormy16a processor.

Behaviors
initialization

The CPU performs a power-on-reset style of operation when the reset! pin is driven.

Other mode settings may be controlled by pins and/or attributes: endian-set!/endian to set endianness, start-pc-set! to set the PC. These are useful if the standard powerup state of the CPU needs to be changed for running a program that expects an initialized environment.

execution

The component executes zero or more instructions when the step! pin is driven. You can specify the maximum number of instructions to be executed via the step-insn-count attribute. If the yield pin is driven in a reentrant fashion while the instruction loop is active, the loop will be exited at the next opportunity. At the end of the loop, the step-cycles output pin is driven with the number of instructions actually executed, though this value is clamped to be at least 1. The insn-count attribute accumulates the total number of instructions executed since reset.

Each instruction is first fetched from memory via the insn-memory accessor, and its decoding traced if the trace-extract? attribute is set to a true value. The decoded form may be cached indefinitely afterwards, although this cache is flushed when the flush-icache pin is driven.

The engine-type attribute specifies whether the "scache" ("semantic cache") or "pbb" ("pseudo basic block") dispatching mechanism is used during execution. The "scache" mode executes each instruction in isolation and checks all triggerpoints after each. If the enable-step-trap? attribute is set, after each instruction, a single-stepping trap is signalled as described in the exceptions/traps behavior below.

The "pbb" mode executes a series of sequential instructions in one uninterruptible sequence, and is thus faster. However, it cannot handle triggerpoints or single-stepping, nor can it respond to icache flushing as quickly. The "pbb" mode is temporarily and transparently downgraded to the "scache" mode when needed.

During the execution of an instruction, this component may make accesses using the data-memory accessor, may update its simulated registers, and may trigger an exception/trap.

tracing

The component can be configured to perform certain kinds of tracing as target programs execute. These are controlled by the family of trace-* boolean attributes. By default, trace output is directed to the standard output stream. The trace-filename attribute allows the user to specify the name of a file where trace output will be collected. A special filename of "-" is used to represent standard output. Trace output files are not appended, but overwritten each time they are opened.

exceptions/traps

When encountering exception/trap conditions such as memory access errors or software interrupts, this component signals the event using the trap pin. (For some traps, the trap-code pin is driven with extra information just beforehand.) An external component may interpret the values in the table below, and declare a disposition for the condition. In the absence of input, the condition will be treated as the hardware would, that is by dispatching to exception vectors, switching processor modes, etc.

The trap codes sent on the trap output pin are:

trap cause trap-code
1 software trap instruction bitmap
2 breakpoint bkpt number
3 system call syscall number
4 invalid instruction n/a
5 memory fault faulting address
6 arithmetic overflow faulting address
7 stepped n/a

The disposition codes returned on the trap input pin are:

trap effect
0 or n/a dispatch as hardware would
1 handled; continue
2 reissue
3 handled; skip instruction and continue
register access

All 16 general purpose registers are accessible as attribute r0 through r15. The pc attribute is also available. The current endianness is available as attribute endian.

This component exports a number of attributes for use by the sw-debug-gdb component. These are the gdb-* attributes, in the "debugger" category. The gdb-register-N group access all registers in gdb's indexing scheme, in raw target byte order. The gdb-register-pc is a special watchable value with no associated attribute. The gdb-num-registers attribute provides the limit for N. The gdb-exp-registers attribute provides a semicolon-separated list of "expedited" register numbers.

The debugger-bus bus provides access to the target program's address space, and is used by gdb to access target memory.

The gdb-breakpoint-big and gdb-breakpoint-little attributes, if present, are used as memory images of software breakpoint instructions for the appropriate run-time endianness mode.

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

Triggerpoints are supported for CPU registers.

inhibit-recursion supported

It prevents harmful recursion from the step! input pin.


Environment:

Related components:

CPUs connect to many components: memory to store data and instructions, a scheduler to provide step! signals, software trap emulators, debugger interfaces. The step-cycles output pin may be used as a N-event-control input for a target scheduler to track an estimate of consumed target time.

Host system:

Some error conditions are signalled by messages to standard error. These include some illegal CPU states caused by the simulated program.


Component Reference:

Component: hw-cpu-xstormy16

pins
namedirectionlegalvaluesbehaviors
endian-set!in1 (big) / 2 (little)initialization
start-pc-set!inany valueinitialization
reset!in0 or 1initialization
trapinoutenum valuesexceptions/traps
trap-codeoutvarious valuesexceptions/traps
step-cyclesout1..step-insn-countexecution
step!inany valueexecution
yieldinanyexecution
flush-icacheinanyexecution

buses
nameaddressesaccessesbehaviors
debugger-busanyanydebugger access

attributes
namecategorylegal valuesdefault valuebehaviors
endianregister'1'/'big'/'2'/'little'biginitialization, register access
trace-extract?settingbooleanfalsetracing
trace-filenamesettingstring-tracing
trace-result?settingbooleanfalsetracing
engine-typesettingscache or pbbpbbexecution
insn-countwatchable registernumber-execution
step-insn-countsettingnumber1execution
enable-step-trap?settingbooleanfalseexecution
rNwatchable registernumber-register access
pcwatchable registernumber-register access
gdb-register-Ndebuggerbyte array-register access
gdb-num-registersdebuggernumber-register access
gdb-exp-registersdebuggernumber list-register access
gdb-breakpoint-bigdebuggerbyte array-register access
gdb-breakpoint-littledebuggerbyte array-register access
state-snapshot-opaque string-state save/restore
step-cycleswatchable pinnumber-execution
trapwatchable pinnumber-execution/traps
trap-codewatchable pinnumber-execution/traps
trace-semantics?settingbooleanfalseinitialization
trace-disassemble?settingbooleanfalseinitialization
trace-counter?settingbooleanfalseinitialization

accessors
nameaccessesbehaviors
data-memoryanyexecution
insn-memorytypically 4-byte accessesexecution