From 3195459c67e88af9c70a89e4d456d248e361575c Mon Sep 17 00:00:00 2001
From: Alejandro Soto <alejandro@34project.org>
Date: Thu, 23 May 2024 20:22:48 -0600
Subject: rtl/gfx/firmware: implement firmware stub

---
 rtl/gfx/firmware/start.S | 64 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 rtl/gfx/firmware/start.S

(limited to 'rtl/gfx/firmware/start.S')

diff --git a/rtl/gfx/firmware/start.S b/rtl/gfx/firmware/start.S
new file mode 100644
index 0000000..c696119
--- /dev/null
+++ b/rtl/gfx/firmware/start.S
@@ -0,0 +1,64 @@
+.section .text.init.enter
+.global _start
+
+_start:
+	li    t0, 0x4a7a7b0c
+	beq   a0, t0, _magic_ok
+	ret
+
+_magic_ok:
+	lui  t0, %hi(__img_start)
+	addi t0, t0, %lo(__img_start)
+	la   t1, __img_start
+	la   t2, _early_copy_end
+	sub  t2, t2, t1
+
+_early_copy_loop:
+	lw   t3, 0(t1)
+	sw   t3, 0(t0)
+	addi t0, t0, 4
+	addi t1, t1, 4
+	addi t2, t2, -4
+	bgtz  t2, _early_copy_loop
+
+	lui  t2, %hi(_running_on_ram)
+	addi t2, t2, %lo(_running_on_ram)
+	jr   t2
+
+_running_on_ram:
+	la   t2, __img_end
+	sub  t2, t2, t0
+
+_full_copy_loop:
+	lw   t3, 0(t1)
+	lw   t4, 4(t1)
+	lw   t5, 8(t1)
+	lw   t6, 12(t1)
+	sw   t3, 0(t0)
+	sw   t4, 4(t0)
+	sw   t5, 8(t0)
+	sw   t6, 12(t0)
+	addi t0, t0, 16
+	addi t1, t1, 16
+	addi t2, t2, -16
+	bgtz t2, _full_copy_loop
+
+.balign 4
+_early_copy_end:
+	la   t0, __bss_start
+	la   t2, __bss_end
+	sub  t2, t2, t0
+
+_clear_bss_loop:
+	sw   zero, 0(t0)
+	sw   zero, 4(t0)
+	sw   zero, 8(t0)
+	sw   zero, 12(t0)
+	addi t0, t0, 16
+	addi t2, t2, -16
+	bgtz t2, _clear_bss_loop
+
+_start_done:
+	la   sp, __stack
+	call main
+	j    .
-- 
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