2. Overview

This is the general flow chart for csrbox:

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

1. 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.
2. 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

**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 :

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

2.3. LISTS OF SUPPORTED CSRS