[修改] 增加freeRTOS

1. 版本FreeRTOSv202212.01，命名为kernel；

kernel/FreeRTOS/Demo/RISC-V-Qemu-virt_GCC/start.S

@@ -0,0 +1,84 @@
+/*
+ * FreeRTOS V202212.01
+ * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ * the Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * https://www.FreeRTOS.org
+ * https://www.github.com/FreeRTOS
+ *
+ */
+
+#include "riscv-virt.h"
+
+	.section .init
+	.globl _start
+	.type _start,@function
+_start:
+	.cfi_startproc
+	.cfi_undefined ra
+.option push
+.option norelax
+	la  gp, __global_pointer$
+.option pop
+
+	// Continue primary hart
+	csrr a0, mhartid
+	li   a1, PRIM_HART
+	bne  a0, a1, secondary
+
+	// Primary hart
+	la sp, _stack_top
+
+	// Load data section
+	la a0, _data_lma
+	la a1, _data
+	la a2, _edata
+	bgeu a1, a2, 2f
+1:
+	LOAD t0, (a0)
+	STOR t0, (a1)
+	addi a0, a0, REGSIZE
+	addi a1, a1, REGSIZE
+	bltu a1, a2, 1b
+2:
+
+	// Clear bss section
+	la a0, _bss
+	la a1, _ebss
+	bgeu a0, a1, 2f
+1:
+	STOR zero, (a0)
+	addi a0, a0, REGSIZE
+	bltu a0, a1, 1b
+2:
+
+	// argc, argv, envp is 0
+	li  a0, 0
+	li  a1, 0
+	li  a2, 0
+	jal main
+1:
+	wfi
+	j 1b
+
+secondary:
+	// TODO: Multicore is not supported
+	wfi
+	j secondary
+	.cfi_endproc