microwatt

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History

Paul Mackerras 0fb207be60 fetch1: Implement a simple branch target cache 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
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LICENSE	Initial import of microwatt	5 years ago
acorn-cle-215.xdc	acorn: Add support for the Acorn CLE 215+	4 years ago
arty_a7.xdc	Arty A7: Document pin connections for on-board headers	4 years ago
clk_gen_bypass.vhd	Fix clk_gen_bypass	5 years ago
clk_gen_ecp5.vhd	Add PLL for ECP5 device	4 years ago
clk_gen_mcmm.vhd	Improve PLL/MMCM clocks configuration	5 years ago
clk_gen_plle2.vhd	acorn: Add support for the Acorn CLE 215+	4 years ago
cmod_a7-35.xdc	Add SPI configuration to Xilinx constraint files	5 years ago
firmware.hex	Add a few more FPGA related files	5 years ago
fpga-random.vhdl	Add random number generator and implement the darn instruction	4 years ago
fpga-random.xdc	Add random number generator and implement the darn instruction	4 years ago
genesys2.xdc	fpga: Add support for Genesys2	4 years ago
hello_world.hex	hello_world: Use new headers and frequency from syscon	5 years ago
main_bram.vhdl	Fix some ghdlsynth issues with fpga_bram	5 years ago
nexys-video.xdc	spi: Add SPI Flash controller	5 years ago
nexys_a7.xdc	Add SPI configuration to Xilinx constraint files	5 years ago
pp_fifo.vhd	pp_fifo: Fix full fifo losing all data on simultaneous push & pop	5 years ago
pp_soc_uart.vhd	uart: Remove combinational loops on ack and stall signal	5 years ago
pp_utilities.vhd	Initial import of microwatt	5 years ago
soc_reset.vhdl	soc_reset: Use counters, add synchronizers	5 years ago
soc_reset_tb.vhdl	Exit cleanly from testbench on success	5 years ago
top-acorn-cle-215.vhdl	acorn: Add support for the Acorn CLE 215+	4 years ago
top-arty.vhdl	fetch1: Implement a simple branch target cache	4 years ago
top-generic.vhdl	fetch1: Implement a simple branch target cache	4 years ago
top-genesys2.vhdl	fpga: Add support for Genesys2	4 years ago
top-nexys-video.vhdl	fetch1: Implement a simple branch target cache	4 years ago