Add the start of a test harness binary

Makefile

@@ -57,6 +57,9 @@ tests/btohex.elf: mem.o hex.o debug.o tests/btohex.o
 tests/tohex.elf: hex.o tests/tohex.o
 	$(LD) -m elf32lriscv -T link.ld $^ -o $@
 
+tests/harness.elf: tests/harness.o
+	$(LD) -m elf32lriscv -T link.ld $^ -o $@
+
 %.o : %.s
 	$(AS) $(ASFLAGS) $< -o $@
 

tests/harness.s

@@ -0,0 +1,57 @@
+# Unit tests harness
+# Read suite name from stdin, then run that suite
+
+.org 0
+# Provide program starting address to linker
+.global _start
+
+# .extern fmt_decimal
+
+/* newlib system calls */
+.set SYSEXIT,  93
+.set SYSREAD, 63
+.set SYSWRITE, 64
+
+.section .rodata
+
+inputs:
+    .word 0, 1, 2, 3, 9, 10, 100, 0x80000000
+inputs_end:
+
+.section .bss
+
+buf: .skip 11
+inbuf: .skip 80
+
+.text
+
+_start:
+    la a0, inbuf
+    li a1, 80
+    jal read
+
+    mv a2, a0           # move bytes read to a2
+    li t0, SYSWRITE     # "write" syscall
+    li a0, 1            # 1 = standard output (stdout)
+    la a1, inbuf        # load address of buffer
+    ecall               # invoke syscall to print the string
+
+    li t0, SYSEXIT      # "exit" syscall
+    la a0, 0            # Use 0 return code
+    ecall               # invoke syscall to terminate the program
+
+
+# Read from stdin
+#    arguments:
+#       a0: address of buffer to read into
+#       a1: number of bytes to read
+#    return:
+#       a0: count of bytes read, or error if < 0
+
+read:
+    li t0, SYSREAD      # "read" syscall
+    mv a2, a1           # bytes to read
+    mv a1, a0           # buffer address
+    li a0, 0            # 0 = standard input (stdin)
+    ecall               # invoke syscall
+    ret