| commit | 3466fb22686a1c77193e17f21cbfec97332bd323 | [log] [tgz] |
|---|---|---|
| author | Jeff DiCorpo <jeffdi@efabless.com> | Sat Dec 17 11:12:51 2022 -0800 |
| committer | Jeff DiCorpo <jeffdi@efabless.com> | Sat Dec 17 11:12:51 2022 -0800 |
| tree | 3ebac35e0f899888d804296dd3f0d0892ec99662 | |
| parent | 66b9102285e369690e0f31cde0cf85401cd1bf2b [diff] |
final gds oasis
This is a small out-of-order RISC-V core written in synthesizable Verilog that supports the RV64IC unprivileged ISA and parts of the privileged ISA, namely M-mode.
1. Fetch
Instructions are fetched from Icache and pushed into a FIFO queue, known as the instruction buffer(fetch buffer) . Looking up the branch target buffer also occurs in this stage, redirecting the fetched instructions as necessary
F0 stage:
PC_gen will generate the correct PC, the pirority is :*Backend-end redirct target -> predicted PC -> PC+4*. Meanwhile, Let PC do hashing with BHR, and get the hash index for Gshare.
F1 stage:
Sent the PC to Icache for instruction request Do*pc+4* Use PC to index a BTB entry and get*pc_pred.* Use the hash value to index Gshare and get*taken or not-taken*.
F2 stage:
The response from Icache is put into a FIFO instruction buffer Sent*pc+4* to the PC_gen In Redirct logic, if Gshare predicts taken, it will sent pc_pred to PC_gen. Otherwise, pc_gen makes no sense.
2. Decode
F3 stage
In this stage, it pulls instructions out of the instruction buffer and generates the appropriate micro-op($\mu$op) to place into the pipeline
3. Issue
F4 stage
The ISA, or “logical”, register specifiers (e.g. x0-x31) are then*renamed* into “physical” register specifiers Every instruction will do dependency check with its previous instruction to decide whether instructions will be double issued. $\mu$op sitting in the head of ROB wait until all of their source registers are ready and they can read their operand then be issued. This is the beginning of the out–of–order piece of the pipeline.
4. Execute F5 stage Instructions enter the Execute stage where the functional units reside. Issued ALU operations perform their calculation and get results.
For load&store instruction, first the address are calculated and put into the FIFO load/store queue. The instrution at the head of the queue sends request to Dcache if Dcache is ready.
5. Wrieback F6 stage results are written back to physical registers when completing instruction and update ROB status
6. Instruction commit The Reorder Buffer (ROB), tracks the status of each instruction in the pipeline. When the head of the ROB is not-busy, the ROB commits the instruction.
Select the current pc address, whether it comes from a jump instruction or whether to judge branch in BTB and gshare or whether it comes from an exception. The default value is pc+4.
Instructions from Icache are put into the instruction buffer.
Perform pc+4 or use the pc from other places.
| signal | I/O | width | description | interaction |
|---|---|---|---|---|
| is_req_pc | I | 1 | judge if btb need wirte in | fu |
| btb_req_pc | I | 32 | btb needed pc | fu |
| btb_predict_target | I | 32 | btb needed target pc | fu |
| prev_pc | I | 32 | pc to gshare | fu |
| prev_branch_in | I | 1 | if this pc is a branch or jump | fu |
| prev_taken | I | 1 | if this branch is taken | fu |
| rd_en | I | 1 | decode is ready and want a instruction | decoder |
| pc_out | O | 32 | a pc out | decoder |
| next_pc_out | O | 32 | this pc out plus 4 | decoder |
| instruction_out | O | 32 | this pc's instruction | decoder |
| valid_real_branch | I | 1 | if fu give a valid real branch | fu |
| real_branch | I | 32 | this real branch or jump branch pc | fu |
| trap | I | 1 | judge trap | writeback |
| mret | I | 1 | judge mret | writeback |
| trap_vector | I | 32 | vector of trap | csr |
| mret_vector | I | 32 | vector of mret | csr |
| stall | I | 1 | if need stall | hazard |
| invalidate | I | 1 | if is invalidate | hazard |
| fetch_address | O | 32 | pc address | busio |
| fetch_data | I | 32 | instruction | busio |
| exception_valid_o | O | 1 | exception valid | csr |
| ecause_o | O | 1 | exception cause | csr |
instructions first go into the BTB, if there is a hit, pc = pc_from_btb; if match fail, PC = PC +4, after execute stage, BTB will be update
| Revision Number | Author | Date | Description |
|---|---|---|---|
| 0.1 | Xinze Wang | 2022.08.10 | init |
| 0.2 | Xinze Wang | 2022.08.18 | update self check |
| signal | I/O | width | description | interaction |
|---|---|---|---|---|
| pc_in | I | 32 | from PC_gen | fetch |
| next_pc_out | O | 32 | =pc_target or =pc_current | fetch |
| token | O | 1 | to instruction buffer | fetch |
| req_pc | I | 32 | update btb | execute |
| predict_target | I | 32 | update btb | execute |
instructions first go into the Gshare, and Gshare will give a prediction, and at execute stage, this prediction will update
content [gshare] entry:
| Revision Number | Author | Date | Description |
|---|---|---|---|
| 0.1 | Qiaowen Yang | 2022.08.10 | init |
| signal | I/O | width | description | interaction |
|---|---|---|---|---|
| pc | I | 32 | from PC_gen | fetch |
| cur_pred | O | 1 | give a prediction | fetch |
| prev_branch_in | I | 1 | whether prev instr is branch | execute |
| prev_taken | I | 1 | whether prev instr taken | execute |
| prev_pred | I | 1 | prev instr pred result | execute |
| prev_mispred | O | 1 | whether prev instr mispred | execute |
| Revision Number | Author | Date | Description |
|---|---|---|---|
| 0.1 | Xinze Wang | 2022.08.10 | init |
content [x_ib] entry:
input/output
| signal | I/O | width | description | interaction |
|---|---|---|---|---|
| pc_in | I | 32 | from PC_gen | fetch |
| next_pc_in | I | 32 | from PC_gen | fetch |
| instruction_in | I | 32 | from PC_gen | fetch |
| pc_out | O | 32 | give to decode | decode |
| next_pc_out | O | 32 | give to decode | decode |
| instruction_out | O | 32 | give to decode | decode |
| wr_en | I | 1 | want write | fetch |
| ins_full | O | 1 | stall pc in | fetch |
| rd_en | I | 1 | judge decode is ready | decode |
This decoder supports RV64I instructions. It gets the instr from fetch unit and gives the result to ROB unit. For branch instr, it will output a stall flag, until everything is ready.
| Revision Number | Author | Date | Description |
|---|---|---|---|
| 0.1 | Guohua Yin | 2022.08.16 | init |
| 0.2 | Guohua Yin | 2022.08.22 | update |
| Item Name | Description |
|---|---|
| decode | decode the instruction in-order from the instruction buffer |
| signal | I/O | width | description | interaction |
|---|---|---|---|---|
| clk | I | 1 | clock signal | |
| rstn | I | 1 | reset signal, active low, asynchronous reset | |
| pc_in | I | 32 | get the pc from fetch unit | instr buffer |
| next_pc_in | I | 32 | get the next pc from fetch unit | instr buffer |
| instruction_in | I | 32 | get the instr from fetch | fetch |
| valid_in | I | 1 | get the valid signal | fetch |
| ready_in | I | 1 | get the ready signal | rob |
| branch_back | I | 1 | handle the branch stall | fu |
| trapped | I | 1 | pipeline control | fu |
| wfi_in | I | 1 | pipeline control | fu |
| csr_data | I | 64 | get csr data | csr |
| csr_readable | I | 1 | flag about reading from csr | csr |
| csr_writeable | I | 1 | flag about writing to csr | csr |
| csr_address | O | 12 | give to csr | csr |
| uses_rs1 | O | 1 | use rs1 | rob |
| uses_rs2 | O | 1 | use rs2 | rob |
| uses_rd | O | 1 | use rd | rob |
| uses_csr | O | 1 | use csr | rob |
| pc_out | O | 32 | give to rob the pc | rob |
| next_pc_out | O | 32 | give to rob the next pc | rob |
| is_csr | O | 1 | flag about csr | rob |
| write_select_out | O | 2 | write select out signal | rob |
| rd_address_out | O | 5 | give to rob | rob |
| csr_address_out | O | 12 | give to rob | rob |
| mret_out | O | 1 | give to rob | rob |
| wfi_out | O | 1 | give to rob | rob |
| ecause_out | O | 4 | give to rob | rob |
| exception_out | O | 1 | exception | rob |
| half | O | 1 | give to rob | rob |
| valid_out | O | 1 | valid flag | rob |
| ready_out | O | 1 | tell fecth can read | fetch |
| csr_read_out | O | 1 | read signal | rob |
| csr_write_out | O | 1 | csr write signal | rob |
| csr_readable_out | O | 1 | csr can be read | rob |
| csr_writeable_out | O | 1 | can write csr | rob |
| csr_data_out | O | 64 | to rob alu | rob |
| imm_data_out | O | 32 | to rob alu about immed-data | rob |
| alu_function_out | O | 3 | to rob alu | rob |
| alu_function_modifier_out | O | 1 | to rob alu | rob |
| alu_select_a_out | O | 2 | alu select signal:a | rob |
| alu_select_b_out | O | 2 | alu select signal:b | rob |
| cmp_function_out | O | 3 | compare function signal | rob |
| jump_out | O | 1 | to rob branch | rob |
| branch_out | O | 1 | to rob branch | rob |
| is_alu_out | O | 1 | to rob (lsu) | rob |
| load_out | O | 1 | to rob (lsu) | rob |
| store_out | O | 1 | to rob (lsu) | rob |
| load_store_size_out | O | 2 | to rob (lsu) | rob |
| load_signed_out | O | 1 | to rob (lsu) | rob |
| Revision Number | Author | Date | Description |
|---|---|---|---|
| 0.1 | Yihai Zhang | 2022.08.12 | init |
| 2.0 | Yifei Zhu | 2022.08.24 | init |
| Item Name | Description |
|---|---|
| rename table | rename the architecture register to physical one |
| rename table backup | rename table recovery from backup when trap or branch |
| free list | record the free physical register address |
| reorder buffer | store the corresponding data of each instruction |
| physical register | - |
| Operation | port | Description |
|---|---|---|
| write | one write port | write from free list when rob ready to be written |
| read | one read port | read when rob ready to be written |
| flush | one flush port | roll back to backup when trap comes |
| reset | - | when reset signal |
| Operation | port | Description |
|---|---|---|
| - | - | used for rename table rolling back itself |
| reset | - | when reset signal |
| Operation | port | Description |
|---|---|---|
| write | two write ports | write when function unit finish |
| read | two read ports | read when rob ready to issue |
| flush | two flush port | set finish bit to regfile to indicate regfile has used |
| reset | - | when reset signal |
| Operation | port | Description |
|---|---|---|
| write | one write port | write when instr commit |
| read | one read port | read when rob ready to be written |
| reset | - | when reset signal |
| Item Name | Width | Description |
|---|---|---|
| rob op | - | to buffer data from decode for the use of pc, lsu, alu, csr and exception |
| use | 1 bit | indicate whether rob is used |
| issue | 1 bit | indicate whether rob issued |
| commit | 1 bit | indicate whether rob is commited |
| finish | 1 bit | indicate whether function unit writeback finished |
| exception | 1 bit | indicate whether the instr raise an exception |
| prs1 | 6 bit | the mapped physical resource reg1 after renaming |
| prs2 | 6 bit | the mapped physical resource reg2 after renaming |
| prd | 6 bit | the mapped physical destination reg after renaming |
| rd | 5 bit | the architecture reg before ranaming |
| lprd | 6 bit | the mapped reg which is replaced |
| Revision Number | Author | Date | Description |
|---|---|---|---|
| 0.1 | Peichen Guo | 2022.08.10 | init |
| Item Name | Description |
|---|---|
| AGU | Address Generation Unit |
| Address Checker | to check address validation |
| Control Unit | to interact with dcache and send stall |
