Vectorblox ORCA
ORCA is an implementation of RISC-V. It is intended to target FPGAs and can be configured as either RV32I a RV32IM code.
ORCA can be used as a standalone processor, but was built to be a host to Vectorblox's Proprietary Matrix processor MXP.
It is possible to select between Wishbone, Avalon, and AXI for the data and instruction Memory Mapped interfaces Specification.
A QSYS component is provided for easy integration into the Altera toolchain.
Building Toolchain
The official RISC-V toolchain is under active development, and is subject to breaking changes from time to time. Because of that we have included a linked a specific version of the toolchain to this repository. If you use a different version of the toolchain, you may have mixed results.
To build the toolchain, set RISCV_INSTALL to be the destination directory for the toolchain, then run
GIT_TOP/tools/riscv-toolchain/build-toolchain.sh.
Sample Systems
We have provided multiple sample projects across different vendor platforms in the systems/ subdirectory.
The first sample system targeting the DE2-115 (found in the TPad or Veek development systems) is located in the de2-115 directory. It uses the Altera toolchain and requires Quartus and Qsys.
A sample system using the Lattice iCEcube2 toolchain is located in the ice40ultra directory. It targets the iCE5LP4K chip.
In the sf2plus directory is a Microsemi SmartFusion2 sample project that targets the M2S150-FC1152 chip. It is built using the Libero toolchain.
The zedboard directory contains a Xilinx sample project that targets the Zynq-7000 XC7Z020-CLG484-1 SoC. It is built using the Vivado toolchain.
In addition to this example system we provide a system targeting a simulator such as modelsim. We use QSYS to help maintain these systems. The Libero tools include BFM models to simulate the SmartFusion2 system, and the Vivado tools include a simulator to debug a generated Vivado design.
Configuring ORCA
Below is an overview of the various generics exposed from the top level to configure ORCA.
BUS TYPE
There are three generics (AVALON_ENABLE , WISHBONE_ENABLE , AXI_ENABLE ) of which only one must
be set to one. An Assertion will be thrown if more than one is enabled. From the QSYS Configuration
box, only Avalon or AXI can be selected.
REGISTER_SIZE (default = 32)
Reserved for future use, must be set to 32
RESET_VECTOR (default = 0x0000 0000)
Address that the first instruction to be executed at reset is located. The automated tests expect the default value.
MULTIPLY_ENABLE (default = 0)
Enable hardware multiplication
DIVIDE_ENABLE (default = 0 )
Enable hardware division (takes 32 cycles)
SHIFTER_MAX_CYCLES (default = 1)
How many cycles a shift operation can take. valid values are 1, 8 and 32. If MULTIPLY_ENABLE is set to 1, this
configuration option is ignored, and the shifter uses the multiplier.
COUNTER_LENGTH (default = 0)
How many bits the mtime register contains. The standard RISC-V dictates 64 bits, but ORCA allows 32 and 0 as valid values as well.
ENABLE_EXCEPTIONS (default = 1)
If this is set to 1, then logic is added to allow the processor to be interrupted by software interrupts.
BRANCH_PREDICTORS (default = 0)
Reserved for when a branch predictor is implemented
PIPELINE STAGES ( default = 5)
Legal values are 4 and 5. If set to 4, the registers on the output side of the register file are eliminated.
LVE_ENABLE (default = 0)
Enable Lightweight Vector Extensions (not publicly available)
SCRATCHPAD_ADDR_BITS (default = 10)
If LVE_ENABLE == 1, the number of address bits gives the size of the scratchpad memory.
ENABLE_EXT_INTERRUPTS (default = 0)
Enable interrupts from the outside world to interrupt the processor. Depends on ENABLE_EXCEPTIONS ==1
NUM_EXT_INTERRUPTS (default = 1)
If ENABLE_EXT_INTERRUPTS = 1 select how many interrupts to support.
FAMILY (default = ALTERA)
Enables certain portability workarounds when using a specific family ("ALTERA", "LATTICE", "MICROSEMI", and "XILINX").
Interrupts
We found that the Platform Level Interrupt controller (PLIC) that was described in the Privileged Specification V1.9 was to complex for our needs, so ORCA has a non-standard but very simple interrupt controller.
We define 2 more 32 bit CSRs, MEIPEND and MEIMASK. Because these registers are a maximum of 32bits wide, ORCA only
supports 32 interrupts natively.MEIMASK is a mask for the external interrupts. If bit n of MEIMASK is set, then
that the nth interrupt is enabled. MEIPEND is connected to the external interrupt lines, and a such is read-only.
| CSR Name | CSR Number | Access |
|---|---|---|
| MEIMASK | 0x7C0 | RW |
| MEIPEND | 0xFC0 | RO |
The Processor is interrupted by an external interrupt on line n if and only if the MIE bit of the MSTATUS CSR is 1 and
bit n of the MEIMASK CSR is set to 1.