Add some basic fat32 code

sw/test_code/fs_test/harness.c

@@ -0,0 +1,21 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define FILE_PATH "fs.fat"
+
+uint32_t lmulii(uint16_t a, uint16_t b) {
+    printf("lmulii: %x * %x = %x\n", a, b, a*b);
+    return a * b;
+}
+
+uint16_t imulii(uint16_t a, uint16_t b) {
+    printf("imulii: %x * %x = %x\n", a, b, a*b);
+    return a * b;
+}
+
+uint8_t SD_readSingleBlock(uint32_t addr, uint8_t *buf, uint8_t *error) {
+    FILE* f = fopen(FILE_PATH, "rb");
+    // fseek(f, addr * 512, SEEK_SET);
+    fread(buf, 512, 1, f);
+}