- /*
- *********************************************************************************************************
- * INITIALIZE A TASK'S STACK
- *
- * Description: This function is called by either OSTaskCreate() or OSTaskCreateExt() to initialize the
- * stack frame of the task being created. This function is highly processor specific.
- *
- * Arguments : task is a pointer to the task code
- *
- * p_arg is a pointer to a user supplied data area that will be passed to the task
- * when the task first executes.
- *
- * ptos is a pointer to the top of stack. It is assumed that 'ptos' points to
- * a 'free' entry on the task stack. If OS_STK_GROWTH is set to 1 then
- * 'ptos' will contain the HIGHEST valid address of the stack. Similarly, if
- * OS_STK_GROWTH is set to 0, the 'ptos' will contains the LOWEST valid address
- * of the stack.
- *
- * opt specifies options that can be used to alter the behavior of OSTaskStkInit().
- * (see uCOS_II.H for OS_TASK_OPT_xxx).
- *
- * Returns : Always returns the location of the new top-of-stack once the processor registers have
- * been placed on the stack in the proper order.
- *
- * Note(s) : (1) Interrupts are enabled when task starts executing.
- *
- * (2) All tasks run in Thread mode, using process stack.
- *
- * (3) There are two different stack frames depending on whether the Floating-Point(FP)
- * co-processor is enabled or not.
- *
- * (a) The stack frame shown in the diagram is used when the FP co-processor is not present and
- * OS_TASK_OPT_SAVE_FP is disabled. In this case, the FP registers and FP Status Control
- * register are not saved in the stack frame.
- *
- * (b) If the FP co-processor is present but the OS_TASK_OPT_SAVE_FP is not set, then the stack
- * frame is saved as shown in diagram (a). Moreover, if OS_TASK_OPT_SAVE_FP is set, then the
- * FP registers and FP Status Control register are saved in the stack frame.
- *
- * (1) When enabling the FP co-processor, make sure to clear bits ASPEN and LSPEN in the
- * Floating-Point Context Control Register (FPCCR).
- *
* +------------+ +------------+
* | | | |
* +------------+ +------------+
* | xPSR | | xPSR |
* +------------+ +------------+
* |Return Addr| |Return Addr |
* +------------+ +------------+
* | LR(R14) | | LR(R14) |
* +------------+ +------------+
* | R12 | | R12 |
* +------------+ +------------+
* | R3 | | R3 |
* +------------+ +------------+
* | R2 | | R0 |
* +------------+ +------------+
* | R1 | | R1 |
* +------------+ +------------+
* | R0 | | R0 |
* +------------+ +------------+
* | R11 | | R11 |
* +------------+ +------------+
* | R10 | | R10 |
* +------------+ +------------+
* | R9 | | R9 |
* +------------+ +------------+
* | R8 | | R8 |
* +------------+ +------------+
* | R7 | | R7 |
* +------------+ +------------+
* | R6 | | R6 |
* +------------+ +------------+
* | R5 | | R5 |
* +------------+ +------------+
* | R4 | | R4 |
* +------------+ +------------+
* (a) | FPSCR |
* +------------+
* | S31 |
* +------------+
* .
* .
* .
* +------------+
* | S1 |
+------------+
* | S0 |
* +------------+
* (b)
*
- * (4) The SP must be 8-byte aligned in conforming to the Procedure Call Standard for the ARM architecture
- *
- * (a) Section 2.1 of the ABI for the ARM Architecture Advisory Note. SP must be 8-byte aligned
- * on entry to AAPCS-Conforming functions states :
- *
- * The Procedure Call Standard for the ARM Architecture [AAPCS] requires primitive
- * data types to be naturally aligned according to their sizes (for size = 1, 2, 4, 8 bytes).
- * Doing otherwise creates more problems than it solves.
- *
- * In return for preserving the natural alignment of data, conforming code is permitted
- * to rely on that alignment. To support aligning data allocated on the stack, the stack
- * pointer (SP) is required to be 8-byte aligned on entry to a conforming function. In
- * practice this requirement is met if:
- *
- * (1) At each call site, the current size of the calling function抯 stack frame is a multiple of 8 bytes.
- * This places an obligation on compilers and assembly language programmers.
- *
- * (2) SP is a multiple of 8 when control first enters a program.
- * This places an obligation on authors of low level OS, RTOS, and runtime library
- * code to align SP at all points at which control first enters
- * a body of (AAPCS-conforming) code.
- *
- * In turn, this requires the value of SP to be aligned to 0 modulo 8:
- *
- * (3) By exception handlers, before calling AAPCS-conforming code.
- *
- * (4) By OS/RTOS/run-time system code, before giving control to an application.
- *
- * (b) Section 2.3.1 corrective steps from the the SP must be 8-byte aligned on entry
- * to AAPCS-conforming functions advisory note also states.
- *
- * " This requirement extends to operating systems and run-time code for all architecture versions
- * prior to ARMV7 and to the A, R and M architecture profiles thereafter. Special considerations
- * associated with ARMV7M are discussed in ?.3.3"
- *
- * (1) Even if the SP 8-byte aligment is not a requirement for the ARMv7M profile, the stack is aligned
- * to 8-byte boundaries to support legacy execution enviroments.
- *
- * (c) Section 5.2.1.2 from the Procedure Call Standard for the ARM
- * architecture states : "The stack must also conform to the following
- * constraint at a public interface:
- *
- * (1) SP mod 8 = 0. The stack must be double-word aligned"
- *
- * (d) From the ARM Technical Support Knowledge Base. 8 Byte stack aligment.
- *
- * "8 byte stack alignment is a requirement of the ARM Architecture Procedure
- * Call Standard [AAPCS]. This specifies that functions must maintain an 8 byte
- * aligned stack address (e.g. 0x00, 0x08, 0x10, 0x18, 0x20) on all external
- * interfaces. In practice this requirement is met if:
- *
- * (1) At each external interface, the current stack pointer
- * is a multiple of 8 bytes.
- *
- * (2) Your OS maintains 8 byte stack alignment on its external interfaces
- * e.g. on task switches"
- *
- **********************************************************************************************************
- */
-
- OS_STK *OSTaskStkInit (void (*task)(void *p_arg), void *p_arg, OS_STK *ptos, INT16U opt)
- {
- OS_STK *p_stk;
-
-
- p_stk = ptos + 1u; /* Load stack pointer */
- /* Align the stack to 8-bytes. */
- p_stk = (OS_STK *)((OS_STK)(p_stk) & 0xFFFFFFF8u);
- /* Registers stacked as if auto-saved on exception */
- *(--p_stk) = (OS_STK)0x01000000uL; /* xPSR */
- *(--p_stk) = (OS_STK)task; /* Entry Point */
- *(--p_stk) = (OS_STK)OS_TaskReturn; /* R14 (LR) */
- *(--p_stk) = (OS_STK)0x12121212uL; /* R12 */
- *(--p_stk) = (OS_STK)0x03030303uL; /* R3 */
- *(--p_stk) = (OS_STK)0x02020202uL; /* R2 */
- *(--p_stk) = (OS_STK)0x01010101uL; /* R1 */
- *(--p_stk) = (OS_STK)p_arg; /* R0 : argument */
-
- /* Remaining registers saved on process stack */
- *(--p_stk) = (OS_STK)0x11111111uL; /* R11 */
- *(--p_stk) = (OS_STK)0x10101010uL; /* R10 */
- *(--p_stk) = (OS_STK)0x09090909uL; /* R9 */
- *(--p_stk) = (OS_STK)0x08080808uL; /* R8 */
- *(--p_stk) = (OS_STK)0x07070707uL; /* R7 */
- *(--p_stk) = (OS_STK)0x06060606uL; /* R6 */
- *(--p_stk) = (OS_STK)0x05050505uL; /* R5 */
- *(--p_stk) = (OS_STK)0x04040404uL; /* R4 */
-
- #if (OS_CPU_ARM_FP_EN > 0u)
- if ((opt & OS_TASK_OPT_SAVE_FP) != (INT16U)0) {
- *--p_stk = (OS_STK)0x02000000u; /* FPSCR */
- /* Initialize S0-S31 floating point registers */
- *--p_stk = (OS_STK)0x41F80000u; /* S31 */
- *--p_stk = (OS_STK)0x41F00000u; /* S30 */
- *--p_stk = (OS_STK)0x41E80000u; /* S29 */
- *--p_stk = (OS_STK)0x41E00000u; /* S28 */
- *--p_stk = (OS_STK)0x41D80000u; /* S27 */
- *--p_stk = (OS_STK)0x41D00000u; /* S26 */
- *--p_stk = (OS_STK)0x41C80000u; /* S25 */
- *--p_stk = (OS_STK)0x41C00000u; /* S24 */
- *--p_stk = (OS_STK)0x41B80000u; /* S23 */
- *--p_stk = (OS_STK)0x41B00000u; /* S22 */
- *--p_stk = (OS_STK)0x41A80000u; /* S21 */
- *--p_stk = (OS_STK)0x41A00000u; /* S20 */
- *--p_stk = (OS_STK)0x41980000u; /* S19 */
- *--p_stk = (OS_STK)0x41900000u; /* S18 */
- *--p_stk = (OS_STK)0x41880000u; /* S17 */
- *--p_stk = (OS_STK)0x41800000u; /* S16 */
- *--p_stk = (OS_STK)0x41700000u; /* S15 */
- *--p_stk = (OS_STK)0x41600000u; /* S14 */
- *--p_stk = (OS_STK)0x41500000u; /* S13 */
- *--p_stk = (OS_STK)0x41400000u; /* S12 */
- *--p_stk = (OS_STK)0x41300000u; /* S11 */
- *--p_stk = (OS_STK)0x41200000u; /* S10 */
- *--p_stk = (OS_STK)0x41100000u; /* S9 */
- *--p_stk = (OS_STK)0x41000000u; /* S8 */
- *--p_stk = (OS_STK)0x40E00000u; /* S7 */
- *--p_stk = (OS_STK)0x40C00000u; /* S6 */
- *--p_stk = (OS_STK)0x40A00000u; /* S5 */
- *--p_stk = (OS_STK)0x40800000u; /* S4 */
- *--p_stk = (OS_STK)0x40400000u; /* S3 */
- *--p_stk = (OS_STK)0x40000000u; /* S2 */
- *--p_stk = (OS_STK)0x3F800000u; /* S1 */
- *--p_stk = (OS_STK)0x00000000u; /* S0 */
- }
- #endif
-
- return (p_stk);
- }
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