1 files changed, 56 insertions, 8 deletions
diff --git a/spiflash/firmware.s b/spiflash/firmware.s
index 338ae5a..9b12f0c 100644
--- a/spiflash/firmware.s
+++ b/spiflash/firmware.s
@@ -1,8 +1,56 @@
-start:
-      li      x1,0xc0000000
-      sw      x0,0(x0)
-loop: lw      x2,0(x0)
-      addi    x2,x2,1
-      sw      x2,0(x1)
-      sw      x2,0(x0)
-      j       loop
+# write RAM code (a sequence of nops followed by ret)
+li      x5,0x00000013   # nop
+sw      x5,4(x0)
+sw      x5,8(x0)
+sw      x5,12(x0)
+sw      x5,16(x0)
+sw      x5,20(x0)
+sw      x5,24(x0)
+sw      x5,28(x0)
+sw      x5,32(x0)
+sw      x5,36(x0)
+sw      x5,40(x0)
+sw      x5,44(x0)
+sw      x5,48(x0)
+sw      x5,52(x0)
+sw      x5,56(x0)
+sw      x5,60(x0)
+sw      x5,64(x0)
+sw      x5,68(x0)
+sw      x5,72(x0)
+sw      x5,76(x0)
+li      x5,0x00008067   # ret
+sw      x5,80(x0)
+
+# setup gpio address in x5
+li      x5,0xc0000000
+sw      x0,0(x5)
+
+# initial entry point into RAM code
+li      x3,4
+
+# initialize RAM counter
+sw      x0,0(x0)
+
+# start of loop. remember this address
+auipc   x4,0
+
+# execute RAM code, come back here
+jalr    x3
+
+# load counter and increment
+lw      x6,0(x0)
+addi    x6,x6,1
+
+# store counter and update gpios
+sw      x6,0(x5)
+sw      x6,0(x0)
+
+# calculate new entry point into RAM code
+slli    x3,x6,2
+andi    x3,x3,63
+addi    x3,x3,4
+
+# execute RAM code, come back to start of loop
+mv      x1,x4
+jr      x3