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firmware/start.S

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+/*
+ * Copyright (c) 2020 Great Scott Gadgets <info@greatscottgadgets.com>
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+.section .init, "ax"
+
+.global _start
+_start:
+    .cfi_startproc
+    .cfi_undefined ra
+
+    /* Set up our global pointer. */
+    .option push
+    .option norelax
+    la gp, __global_pointer$
+    .option pop
+
+    /* Set up our stack. */
+    la sp, __stack_top
+    add s0, sp, zero
+
+    /*
+     * NOTE: In most cases, we'd clear the BSS, here.
+     *
+     * In our case, our FPGA automaticaly starts with all of our RAM
+     * initialized to zero; so our BSS comes pre-cleared. We'll skip the
+     * formality of re-clearing it.
+     */
+
+    /* Finally, start our main routine. */
+    jal zero, main
+
+    .cfi_endproc
+    .end