建立工程，成功创建两个虚拟串口

source/rt_thread/libcpu/arm/arm926/context_gcc.S

@@ -0,0 +1,79 @@
+;/*
+; * Copyright (c) 2006-2018, RT-Thread Development Team
+; *
+; * SPDX-License-Identifier: Apache-2.0
+; *
+; * Change Logs:
+; * Date           Author       Notes
+; * 2011-08-14     weety    copy from mini2440
+; */
+
+#define NOINT   0xC0
+
+.text
+;/*
+; * rt_base_t rt_hw_interrupt_disable();
+; */
+    .globl rt_hw_interrupt_disable
+rt_hw_interrupt_disable:
+    MRS     R0, CPSR
+    ORR     R1, R0, #NOINT
+    MSR     CPSR_c, R1
+    BX      LR
+
+/*
+ * void rt_hw_interrupt_enable(rt_base_t level);
+ */
+    .globl rt_hw_interrupt_enable
+rt_hw_interrupt_enable:
+    MSR     CPSR, R0
+    BX      LR
+
+/*
+ * void rt_hw_context_switch(rt_uint32 from, rt_uint32 to);
+ * r0 --> from
+ * r1 --> to
+ */
+    .globl rt_hw_context_switch
+rt_hw_context_switch:
+    STMFD   SP!, {LR}           @; push pc (lr should be pushed in place of pc)
+    STMFD   SP!, {R0-R12, LR}       @; push lr & register file
+    MRS     R4, CPSR
+    STMFD   SP!, {R4}               @; push cpsr
+    STR     SP, [R0]                @; store sp in preempted tasks tcb
+    LDR     SP, [R1]                @; get new task stack pointer
+    LDMFD   SP!, {R4}               @; pop new task spsr
+    MSR     SPSR_cxsf, R4
+    LDMFD   SP!, {R0-R12, LR, PC}^  @; pop new task r0-r12, lr & pc
+
+/*
+ * void rt_hw_context_switch_to(rt_uint32 to);
+ * r0 --> to
+ */
+    .globl rt_hw_context_switch_to
+rt_hw_context_switch_to:
+    LDR     SP, [R0]                @; get new task stack pointer
+    LDMFD   SP!, {R4}               @; pop new task cpsr
+    MSR     SPSR_cxsf, R4
+    LDMFD   SP!, {R0-R12, LR, PC}^  @; pop new task r0-r12, lr & pc
+
+/*
+ * void rt_hw_context_switch_interrupt(rt_uint32 from, rt_uint32 to);
+ */
+    .globl rt_thread_switch_interrupt_flag
+    .globl rt_interrupt_from_thread
+    .globl rt_interrupt_to_thread
+    .globl rt_hw_context_switch_interrupt
+rt_hw_context_switch_interrupt:
+    LDR     R2, =rt_thread_switch_interrupt_flag
+    LDR     R3, [R2]
+    CMP     R3, #1
+    BEQ     _reswitch
+    MOV     R3, #1                          @; set flag to 1
+    STR     R3, [R2]
+    LDR     R2, =rt_interrupt_from_thread   @; set rt_interrupt_from_thread
+    STR     R0, [R2]
+_reswitch:
+    LDR     R2, =rt_interrupt_to_thread     @; set rt_interrupt_to_thread
+    STR     R1, [R2]
+    BX      LR