diff --git a/Makefile b/Makefile
index d53b7ae..6c1eb51 100644
--- a/Makefile
+++ b/Makefile
@@ -17,11 +17,14 @@ hello.elf: hello.o
calc.elf: hex.o calc.o
$(LD) -m elf32lriscv -T link.ld $^ -o $@
-tests: tests/btohex.elf
+tests: tests/btohex.elf tests/tohex.elf
tests/btohex.elf: hex.o tests/btohex.o
$(LD) -m elf32lriscv -T link.ld $^ -o $@
+tests/tohex.elf: hex.o tests/tohex.o
+ $(LD) -m elf32lriscv -T link.ld $^ -o $@
+
%.o : %.s
$(AS) $(ASFLAGS) $< -o $@
diff --git a/calc.s b/calc.s
index 0504e50..d1be333 100644
--- a/calc.s
+++ b/calc.s
@@ -160,14 +160,3 @@ memcpy_loop:
j memcpy_loop
memcpy_done:
ret
-
-# Write hex representation into buffer
-# arguments:
-# a0: value to format
-# a1: address of buffer to write to
-# temporaries used:
-# t0
-# return:
-# none
-tohex:
-
diff --git a/hex.s b/hex.s
index d5f0c2a..034f72e 100644
--- a/hex.s
+++ b/hex.s
@@ -1,4 +1,5 @@
.global btohex
+.global tohex
.section .rodata
hexchars:
@@ -6,6 +7,35 @@ hexchars:
.text
+# Write hex representation of word into buffer
+# arguments:
+# a0: value to format
+# a1: address of buffer to write to
+# temporaries used:
+# t0
+# return:
+# none
+tohex:
+ li s0, 0 # set up loop variables
+ li s1, 4
+ addi a1, a1, 6 # offset output address to end chars
+ addi sp, sp, -12 # allocate stack space
+tohex_loop:
+ sw ra, 8(sp) # save contents of ra
+ sw a0, 4(sp) # save contents of ra
+ sw a1, 0(sp) # save contents of ra
+ jal btohex
+ lw a1, 0(sp) # restore contents of a1
+ sh a0, 0(a1) # write the two bytes to the output buffer
+ lw a0, 4(sp) # restore contents of a0
+ lw ra, 8(sp) # restore contents of ra
+ srli a0, a0, 8 # shift the next byte to format down
+ addi a1, a1, -2 # decrement output buffer address
+ addi s0, s0, 1 # increment loop counter
+ blt s0, s1, tohex_loop # TODO: we don't need the loop counter and output addr
+ addi sp, sp, 12 # deallocate stack space
+ ret
+
# Convert byte to ASCII hex
# arguments:
# a0: value to format
@@ -14,16 +44,15 @@ hexchars:
# return:
# a0: value in ASCII hex
btohex:
- andi t0, a0, 0xF # Mask off lower nybble
- la a1, hexchars # load address of hexchars
- add a2, a1, t0 # offset to nybble
- lbu t0, 0(a2) # load hex char at offset
- srli t1, a0, 4 # shift upper nybble down
- andi t1, t1, 0xF # mask off upper nybble
- add a2, a1, t1 # offset to nybble
- lbu t1, 0(a2) # load hex char at offset
- mv a0, t1 # copy upper char to a0
- slli a0, a0, 8 # shuft upper char up
- or a0, a0, t0 # OR the lower char into a0
- ret
+ la a1, hexchars # load address of hexchars
+ andi t0, a0, 0xF # Mask off lower nybble
+ add a2, a1, t0 # a2 = offset to nybble hex char
+ lbu t0, 0(a2) # load hex char for lower nybble into t0
+ srli t1, a0, 4 # shift upper nybble down
+ andi t1, t1, 0xF # mask off upper nybble
+ add a2, a1, t1 # offset to nybble
+ lbu a0, 0(a2) # load hex char for upper nybble into a0
+ slli t0, t0, 8 # shift lower char up (little endian)
+ or a0, a0, t0 # OR the lower char into a0
+ ret
diff --git a/tests/test_btohex.sh b/tests/test_btohex.sh
deleted file mode 100644
index c39f321..0000000
--- a/tests/test_btohex.sh
+++ /dev/null
@@ -1,10 +0,0 @@
-#!/bin/sh
-
-test_btohex() {
- # FIXME: Remove grep when this bug is fixed:
- # https://github.com/sysprog21/rv32emu/issues/561
- result=$("${RV32EMU}" -d - -q tests/btohex | grep -v '^\d' | "${JQ}" .x11)
-
- test $? -eq 0 && test "${result}" -eq 16693 # 16693 is A5 in ASCII
-}
-
diff --git a/tests/test_hex.sh b/tests/test_hex.sh
new file mode 100644
index 0000000..0ad1be0
--- /dev/null
+++ b/tests/test_hex.sh
@@ -0,0 +1,18 @@
+#!/bin/sh
+
+test_btohex() {
+ # FIXME: Remove grep when this bug is fixed:
+ # https://github.com/sysprog21/rv32emu/issues/561
+ result=$("${RV32EMU}" -d - -q tests/btohex.elf | grep -v '^\d' | "${JQ}" .x11)
+
+ # 16693 is 5A in ASCII (reversed from input due to little endian)
+ test $? -eq 0 && test "${result}" -eq 13633
+}
+
+test_tohex() {
+ # FIXME: Remove grep when this bug is fixed:
+ # https://github.com/sysprog21/rv32emu/issues/561
+ result=$("${RV32EMU}" -q tests/tohex.elf | grep -v '^\d')
+
+ test $? -eq 0 && test "${result}" = "CAFEFEED"
+}
diff --git a/tests/tohex.s b/tests/tohex.s
new file mode 100644
index 0000000..ee2a7b7
--- /dev/null
+++ b/tests/tohex.s
@@ -0,0 +1,32 @@
+# Test for btohex
+
+.org 0
+# Provide program starting address to linker
+.global _start
+
+.extern tohex
+
+/* newlib system calls */
+.set SYSEXIT, 93
+.set SYSWRITE, 64
+
+.section .bss
+buf: .skip 9
+
+.text
+_start:
+ li a0, '\n
+ la a1, buf
+ sb a0, 8(a1) # append newline to buf
+ li a0, 0xCAFEFEED
+ jal tohex
+
+ li t0, SYSWRITE # "write" syscall
+ li a0, 1 # 1 = standard output (stdout)
+ la a1, buf # load address of output string
+ li a2, 9 # length of output string
+ 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