2. Overview¶

This is the general flow chart for csrbox:

The user is required to provide 2 YAML files as input:

ISA Spec: This YAML file is meant to capture the ISA related features implemented by the user. This is first fed into riscv-config python and the standard isa spec is finally put into the csrbox.
Grouping Spec: This YAML file is meant to capture how the csrs are grouped together by the user. Details of this input file can be found here : Group yaml dependencies.

2.1. Current CSR support¶

The current version of Csrbox- 1.0.1 supports all machine mode csrs, corresponding supervisor mode and user mode csrs that depend only on ‘U’ extension . For the complete list of csrs, refer here : LISTS OF SUPPORTED CSRS.

2.2. Working¶

INPUT:

The isa spec is first passed through riscv config to get the standard isa spec as the intermediate input to csrbox.

PROCESS:

The csrs present in both the grouping yaml as well std isa spec and are consecutively checked for the :

Size of the csr ( if subfields exists, the check is for highest msb value)

Description of csr

Address of the csr for decoder

Shadow csrs

Attribute Yaml
The attribute yaml is used to automate the process of checking for shadows, dependent csrs, special case action methods and subfields internally. The general structure includes :

Value method

Action method

definition argument

declaration body

Dependencies

interface method definition

register instantiation

module declaration

csrbox main mkconnection() {to connect the value method from the group csr is being extracted from}

Note: Any additions to the attributes yaml should be done in terms of bluespec code and not as running commentary

CSR Decoder
The decoder is a bluespec demultiplexer like function that checks the validity of the given csr address. The job of the function is to compare the given address with all the csrbox supported address . If it is able to match, a bool variable becomes valid, else is turned false.

CSR Defines
It consists of automatically generated macros for all csrs corresponding with their addresses. This is done after reading the isa yaml file for the right addresses.

WARL Support
The function first splits the warl string into the condition and the legalizing strings. A regular expression is then applied to both strings separately to extract parameters and create bluespec code.

OUTPUT:

All output files are automatically placed under the work directory with the intermediate isa file in it and the bluespec files in a separate folder. These bluespec files are generated after successful bluesim and verilog compilation.

The files generated are :

Csrbox main file to moderate the groups

Individual group bsv files

CSR Decoder

CSR Defines

CSR types

ISA checked file

CSR flow in Daisy Chain
All core requests consists of the following :

Address of the csr

Data to written

Two bit operands(funct3) to determine if data is to write/read

Data flows from one group to another in a daisy chain manner until it hits the right group. If there is a miss in the first group , using an actionvalue method and a fifo the core request is forwarded to the next node.

Once there is hit, a CSR Response is recorded consisting of:

Bool variable to indicate the hit

Data that has been read

2.3. LISTS OF SUPPORTED CSRS¶

MACHINE CSRS
MVENDORID
MARCHID
MIMPID
MHARTID
MISA
MTVEC
MEDELEG
MIDELEG
MIE
MCOUNTEREN
MSTATUS
MIP
MSCRATCH
MEPC
MCAUSE
MTVAL
PMPCFG0
PMPCFG1
PMPCFG2
PMPCFG3
.
.
.
PMPCFG14
PMPCFG15
PMPADDR0
PMPADDR1
PMPADDR2
.
.
.
.
.
PMPADDR63
MCYCLE
MINSTRET
MHPMCOUNTER3
MHPMCOUNTER4
.
.
.
.
MHPMCOUNTER31
MCYCLEH
MINSTRETH
MHPMCOUNTER3H
MHPMCOUNTER4H
.
.
.
.
MHPMCOUNTER31H
MCOUTNINHIBIT
MHPMEVENT3
MHPMEVENT4
.
.
.
.
MHPMEVENT31

USER CSRS
USTATUS
UIP
UIE
UTVEC
UEPC
UTVAL
UCAUSE
USCRATCH
CYCLE
INSTRET
HPMCOUNTER3
HPMCOUNTER4
.
.
.
.
HPMCOUNTER31
CYCLEH
INSTRETH
HPMCOUNTER3H
HPMCOUNTER4H
.
.
.
.
HPMCOUNTER31H
TIME
TIMEH
FFLAGS
FRM
FCSR

SUPERVISOR CSRS
SSTATUS
SEDELEG
SIDELEG
SIE
STVEC
SSCRATCH
SEPC
SCAUSE
STVAL
SIP
SATP
SSCRATCH
SCOUNTEREN
SIDELEG
SEDELEG