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HSC Latte HS32 Core

The HSC Latte HS32 Core is a 32-bits RISC CPU. The HS32 Core has 32-bits instructions and 16 32-bits registers.

Below is a list of HS32 Core Project Directories:

| Repository | Description | License | Issues | Stars | Contributors | | ----------------------------------------------------------------- | ----------------------- | ---------------------------------------------------------------------------- | -------------------------------------------------------------------------- | ------------------------------------------------------------------------ | -------------------------------------------------------------------------------------- | | caravel-hs32core | Core Harness | License | Issues | Stars | Contributors | | hs32core-rtl | RTL Circuit Design | License | Issues | Stars | Contributors | | hs32core | Main Project Repository | License | Issues | Stars | Contributors |

Table of Contents


HS32 is a RISC-type CPU. (...)

Block Diagram Overview

CPU Overview

Execution Unit Block Diagram

Execution Unit

Project Structure

| Path | Description | |-|-| | verilog/rtl/hs32cpu | CPU Core Submodule | | verilog/rtl/hs32_user_proj | User project files and wrapper | | verilog/rtl/hs32cpu/docs | Detailed core documentation | | verilog/dv/hs32_nocaravel | No-caravel testbenches | | verilog/dv/caravel/hs32_soc | Caravel-integrated testbenches |

General Documentation


  • Immediate value is 16-bits
  • Rd, Rn and Rm specify the way each register is wired to the ALU. In this case, Rd represents the read/write source/destination, Rm and Rn represents the 2 operands fed into the ALU; note that Rn will always have a barrel shifter in front of it.
  • Naming a register with Rd Rn Rm is always 4 bits
  • [xxx] = Dereference pointer, address is stored in xxx
  • sh(Rn) shifts contents of Rn left or right by an 5-bits amount


These are the different encodings that instructions come in. All instructions are 32 bit. The first 8 bits is opcode. Rd, Rm, Rn are always in the same position in the instruciton if present indicates unused spacer value of X bits

  • Field Sizes:
  • Rd : 4 bit register name
  • Rm : 4 bit register name
  • Rn : 4 bit register name
  • Shift: 5 bit shift amount applied to Rn
  • Imm16: 16 bit literal field
Name [0:3] [4:7] [8:11] [12:15] [16:19] [20:23] [24:27] [28:31]
Opcode Rd Rm Imm16
Opcode Rd Rm Rn Shift Shift | Shift Direction | Register Bank Register Bank | XXX

System Details

There are 16 (r0-r15) general-purpose registers plus 4 privileged registers. In supervisor mode, r12-15 is separate from user-mode r12-15. In all modes, r14 and r15 will be used as the link register and stack pointer respectively.


  • IRQs -- Interrupt Requests
  • SP -- Stack Pointer
  • LR -- Link Register
  • MCR -- Machine Configuration Register
  • IVT -- Interrupt Vector Table
Register Alias/Description
User IRQ Supervisor
Shared general purpose registers
r12 General
Interrupt Vector Table
r13 General
Machine Configuration Register
r14 User LR IRQ LR Super LR
r15 User SP IRQ SP Super SP


During a mode switch, the return address will be stored in the appropriate LR and the return stack pointer will be stored in the appropriate SP.

For instance, an interrupt call from User mode will prompt a switch to IRQ mode. The return address and stack pointer of the caller will be stored in IRQ LR (r14) and IRQ SP (r15) respectively.

CPU Planned Pinout


Devboard Block Diagram

Timing Waveforms

Various timing diagrams of the address and data buses

Read Cycle

Clock Cycles: 4 minimum

Timing Requirements: - The duration of the TW read clock (no data input) is determined by the tpd of whichever memory chip used. - TW can span multiple clock periods to allow for different memory timings. This will allow the CPU to be clocked at a higher speed than the memory chips.

In the implementation, OE# is the AND of 2 signals, one leading edge and one falling edge-driven signals.

Write Cycle

Clock Cycles: 4 minimum

Timing Requirements: - See the read cycle specifications


Apache 2.0 LICENSE

HS32 Core - A 32-bits RISC Processor

``` Copyright (c) 2020 The HSC Core Authors

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. ```

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Open Source Hardware Processor