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Configurable RISC-V Processor
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Ross Thompson 75b97f1422 Created special test for driving the instruction spill error. 
The extact problem occurs when a 4 byte instruction startles two cache blocks (or without a cache two ahbi words) and the code jumps to a cache block other than the next cache block. Consider the following sample of code.

0000000000000080 <test_spill>:
  80:	42a9                	li	t0,10
  82:	0001                	nop
  84:	0001                	nop
  86:	0001                	nop
  88:	02bd                	addi	t0,t0,15
  8a:	00628e33          	add	t3,t0,t1
  8e:	01ce8963          	beq	t4,t3,a0 <match>

0000000000000092 <failure>:
  92:	557d                	li	a0,-1
  94:	8082                	ret
  96:	00000013          	nop
  9a:	00000013          	nop
  9e:	0001                	nop

00000000000000a0 <match>:
  a0:	1ffd                	addi	t6,t6,-1
  a2:	fc0f9fe3          	bnez	t6,80 <test_spill>
  a6:	4501                	li	a0,0
  a8:	8082                	ret

Instructions 0x88, 0x8a and 0x8e are read incorrectly.  However once the branch predictor begins to correctly predict the beq at 0x8e the instrution at 0xa0 is loaded incorrectly as the 2 upper bytes of 0x8e and the two bytes of 0x92.  This amalgamation causes c.addi at 0xa0 to do something else and the loop never terminates.

The button of wavefile wave.do shows the exact problem in the 'icache'.
2021-04-08 15:05:08 -05:00
sky130 sky130 18T and 15T cell libraries removed 2021-02-14 09:05:41 -06:00
testsBP Created special test for driving the instruction spill error. 2021-04-08 15:05:08 -05:00
wally-pipelined Created special test for driving the instruction spill error. 2021-04-08 15:05:08 -05:00
.gitignore Merge of main with the new icache and the branch predictor. I believe there is a bug in the icache with unaligned memory access. The second part of the access is incorrectly relying on the PCF being the address of the next two bytes of the instruction. However this is not always the case as the branch predictor can get the wrong target address. The icache needs to generate the +2 address internally. 2021-03-30 23:18:20 -05:00
.gitmodules sky130 18T and 15T cell libraries removed 2021-02-14 09:05:41 -06:00
LICENSE Initial Checkin 2021-01-14 23:37:51 -05:00
README.md Initial commit 2021-01-14 20:16:47 -08:00

README.md

riscv-wally

Configurable RISC-V Processor