added ebreak support

Makefile

@@ -15,6 +15,11 @@ rv32imac_tests.bin: rv32imac_tests.elf
 
 run: rv32imac_tests.bin
 	$(EMULATOR) rv32imac_tests.bin
+	@echo "Testing standard ebreak..."
+	@echo "115 0 16 0" | awk -f amach.awk 2>&1 | grep -q "Fatal: EBREAK"
+	@echo "Testing compressed c.ebreak..."
+	@echo "2 144" | awk -f amach.awk 2>&1 | grep -q "Fatal: EBREAK"
+	@echo "All EBREAK tests PASSED!"
 
 clean:
 	rm -f rv32imac_tests.elf rv32imac_tests.bin

README.md

@@ -32,7 +32,7 @@ POSIXLY_CORRECT=1 awk -f amach.awk [-v LVA=...] -- path/to/program.dec
 
 ## Support
 
-Currently, A-machine only supports the **unprivileged** RV32IMAC instruction set with a few additional `ecall` syscalls: 63 (sys_read, for fd 0 only), 64 (sys_write, for fd 1 and 2 only) and 93 (sys_exit). For completeness, `fence` instruction is also supported but yields a no-op.
+Currently, A-machine only supports the **unprivileged** RV32IMAC instruction set with a few additional `ecall` syscalls: 63 (sys_read, for fd 0 only), 64 (sys_write, for fd 1 and 2 only) and 93 (sys_exit). For completeness, `fence` instruction is also supported but yields a no-op, and both `ebreak` and `c.ebreak` are supported to halt execution with a debug message.
 
 ## Plans (from higher to lower priority)
 

amach.awk

@@ -170,6 +170,7 @@ function amach_imm(opcode, f3, rd, rs1, immval,  r1, ur1, shamt) {
     pc = r1 + immval
   } else if(opcode == 115) { # 0x73, system call / csr
     if(immval == 0) handle_ecall(getreg(17), getreg(10), getreg(11), getreg(12), getreg(13), getreg(14), getreg(15))
+    else if(immval == 1) trapout(sprintf("EBREAK at 0x%X", pc-4))
     else trapout(sprintf("Unimplemented external system call at 0x%X", pc-4))
   } else trapout(sprintf("Illegal instruction at 0x%X", pc-4))
 }
@@ -317,9 +318,8 @@ function amach_comp(instr,  op, f3, b12, r11_7, r9_7, r6_2, r4_2, shamt, imm, ba
         } else setreg(r11_7, getreg(r6_2)) # C.MV
       } else {
         if(r6_2 == 0) {
-          if(r11_7 == 0) { # C.EBREAK
-            trapout(sprintf("EBREAK at 0x%X", pc-2))
-          } else { # C.JALR
+          if(r11_7 == 0) trapout(sprintf("EBREAK at 0x%X", pc-2)) # C.EBREAK
+          else { # C.JALR
             imm = getreg(r11_7)
             setreg(1, pc)
             pc = imm

rv32imac_tests.s

@@ -795,6 +795,12 @@ _start:
   li a7, 93
   ecall
 
+  # Unreachable: placed to verify standard/compressed ebreak compilation
+  ebreak
+  .option rvc
+  c.ebreak
+  .option norvc
+
 report_error:
   la a0, str_some_failed
   jal print_string