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Paul Mackerras
0fb207be60
This implements a cache in fetch1, where each entry stores the address of a simple branch instruction (b or bc) and the target of the branch. When fetching sequentially, if the address being fetched matches the cache entry, then fetching will be redirected to the branch target. The cache has 1024 entries and is direct-mapped, i.e. indexed by bits 11..2 of the NIA. The bus from execute1 now carries information about taken and not-taken simple branches, which fetch1 uses to update the cache. The cache entry is updated for both taken and not-taken branches, with the valid bit being set if the branch was taken and cleared if the branch was not taken. If fetching is redirected to the branch target then that goes down the pipe as a predicted-taken branch, and decode1 does not do any static branch prediction. If fetching is not redirected, then the next instruction goes down the pipe as normal and decode1 does its static branch prediction. In order to make timing, the lookup of the cache is pipelined, so on each cycle the cache entry for the current NIA + 8 is read. This means that after a redirect (from decode1 or execute1), only the third and subsequent sequentially-fetched instructions will be able to be predicted. This improves the coremark value on the Arty A7-100 from about 180 to about 190 (more than 5%). The BTC is optional. Builds for the Artix 7 35-T part have it off by default because the extra ~1420 LUTs it takes mean that the design doesn't fit on the Arty A7-35 board. Signed-off-by: Paul Mackerras <paulus@ozlabs.org> |
4 years ago | |
|---|---|---|
| .. | ||
| LICENSE | ||
| acorn-cle-215.xdc | ||
| arty_a7.xdc | ||
| clk_gen_bypass.vhd | ||
| clk_gen_ecp5.vhd | ||
| clk_gen_mcmm.vhd | ||
| clk_gen_plle2.vhd | ||
| cmod_a7-35.xdc | ||
| firmware.hex | ||
| fpga-random.vhdl | ||
| fpga-random.xdc | ||
| genesys2.xdc | ||
| hello_world.hex | ||
| main_bram.vhdl | ||
| nexys-video.xdc | ||
| nexys_a7.xdc | ||
| pp_fifo.vhd | ||
| pp_soc_uart.vhd | ||
| pp_utilities.vhd | ||
| soc_reset.vhdl | ||
| soc_reset_tb.vhdl | ||
| top-acorn-cle-215.vhdl | ||
| top-arty.vhdl | 4 years ago | |
| top-generic.vhdl | 4 years ago | |
| top-genesys2.vhdl | ||
| top-nexys-video.vhdl | 4 years ago | |