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[docs][libcpu][arm][cortex-a] update comment for start_gcc.S #11089

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97 changes: 58 additions & 39 deletions libcpu/arm/cortex-a/start_gcc.S
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Original file line number Diff line number Diff line change
Expand Up @@ -27,13 +27,24 @@
.equ I_Bit, 0x80 /* when I bit is set, IRQ is disabled */
.equ F_Bit, 0x40 /* when F bit is set, FIQ is disabled */

/*Load the physical address of a symbol into a register.
Through pv_off calculates the offset of the physical address */
/**
* @brief get the physical address of the symbol
*
* @param reg register to store the physical address
* @param symbol symbol name
* @param _pvoff the offset between the physical address and the virtual address
*/
.macro get_phy, reg, symbol, _pvoff
ldr \reg, =\symbol
add \reg, \_pvoff
.endm
/*Calculate the offset between the physical address and the virtual address of the "_reset".*/

/**
* @brief calculate the offset between the physical address and the virtual address of the "_reset"
*
* @param tmp register which will be used to store the virtual address of the "_reset"
* @param out register which will be used to store the pv_off (paddr - vaddr)
*/
.macro get_pvoff, tmp, out
ldr \tmp, =_reset
adr \out, _reset
Expand Down Expand Up @@ -68,20 +79,20 @@ init_cpu_stack_early:

#ifdef RT_USING_FPU
mov r4, #0xfffffff
mcr p15, 0, r4, c1, c0, 2
mcr p15, 0, r4, c1, c0, 2 /* CPACR */
#endif

mov pc, lr

init_kernel_bss:

/* enable I cache + branch prediction */
mrc p15, 0, r0, c1, c0, 0
orr r0, r0, #(1<<12)
orr r0, r0, #(1<<11)
mrc p15, 0, r0, c1, c0, 0 /* SCTLR */
orr r0, r0, #(1<<12) /* I=1 */
orr r0, r0, #(1<<11) /* Z=1 */
mcr p15, 0, r0, c1, c0, 0

mov r0,#0 /* get a zero */
mov r0,#0
get_phy r1, __bss_start, pv_off
get_phy r2, __bss_end, pv_off

Expand Down Expand Up @@ -123,7 +134,7 @@ continue_exit:
#endif
#ifdef SOC_BCM283x
/* Suspend the other cpu cores */
mrc p15, 0, r0, c0, c0, 5
mrc p15, 0, r0, c0, c0, 5 /* MPIDR */
ands r0, #3
bne _halt

Expand Down Expand Up @@ -162,17 +173,18 @@ continue_exit:

#endif

/* invalid tlb before enable mmu */
mrc p15, 0, r0, c1, c0, 0
bic r0, #1
/* disable MMU */
mrc p15, 0, r0, c1, c0, 0 /* SCTLR */
bic r0, #1 /* M=0 */
mcr p15, 0, r0, c1, c0, 0
dsb
isb

/* invalidate TLB, I-cache and branch predictor */
mov r0, #0
mcr p15, 0, r0, c8, c7, 0
mcr p15, 0, r0, c7, c5, 0 /* iciallu */
mcr p15, 0, r0, c7, c5, 6 /* bpiall */
mcr p15, 0, r0, c8, c7, 0 /* ITLBIALL */
mcr p15, 0, r0, c7, c5, 0 /* ICIALLU */
mcr p15, 0, r0, c7, c5, 6 /* BPIALL */
dsb
isb

Expand Down Expand Up @@ -218,13 +230,14 @@ enable_mmu_page_table_early:
get_phy r0, init_mtbl, pv_off
mcr p15, #0, r0, c2, c0, #0
dmb

ldr r0,=#0x55555555
mcr p15, #0, r0, c3, c0, #0

/* set all domains with client mode */
ldr r0,=#0x55555555 /* client */
mcr p15, #0, r0, c3, c0, #0 /* DACR */

/* disable ttbr1 */
mov r0, #(1 << 5) /* PD1=1 */
mcr p15, 0, r0, c2, c0, 2 /* ttbcr */
mov r0, #(1 << 5) /* PD1=1 */
mcr p15, 0, r0, c2, c0, 2 /* TTBCR */


/* init stack for cpu mod */
Expand Down Expand Up @@ -253,16 +266,17 @@ enable_mmu_page_table_early:
sub sp, r1, cpu_id, asl #ARM_CPU_STACK_SIZE_OFFSET


/* invalid tlb before enable mmu */
/* invalidate TLB, I-cache and branch predictor */
mov r0, #0
mcr p15, 0, r0, c8, c7, 0
mcr p15, 0, r0, c7, c5, 0 /* iciallu */
mcr p15, 0, r0, c7, c5, 6 /* bpiall */

mrc p15, 0, r0, c1, c0, 0
bic r0, r0, #0x7 /* clear bit1~3 */
orr r0, #((1 << 12) | (1 << 11)) /* instruction cache, branch prediction */
orr r0, #((1 << 2) | (1 << 0)) /* data cache, mmu enable */
mcr p15, 0, r0, c8, c7, 0 /* ITLBIALL */
mcr p15, 0, r0, c7, c5, 0 /* ICIALLU */
mcr p15, 0, r0, c7, c5, 6 /* BPIALL */

/* enable I cache + branch prediction, enable MMU */
mrc p15, 0, r0, c1, c0, 0 /* SCTLR */
bic r0, r0, #0x7 /* C=0, A=0, M=0 */
orr r0, #((1 << 12) | (1 << 11)) /* I=1, Z=1 */
orr r0, #((1 << 2) | (1 << 0)) /* C=1, M=1 */
mcr p15, 0, r0, c1, c0, 0
dsb
isb
Expand All @@ -278,13 +292,13 @@ master_core_startup :

.global rt_hw_mmu_tbl_get
rt_hw_mmu_tbl_get:
mrc p15, 0, r0, c2, c0, 0 /* ttbr0 */
bic r0, #0x18
mrc p15, 0, r0, c2, c0, 0 /* TTBR0 */
bic r0, #0x18 /* RGN=0 */
mov pc, lr

.weak rt_hw_cpu_id_early
rt_hw_cpu_id_early:
mrc p15, 0, r0, c0, c0, 5
mrc p15, 0, r0, c0, c0, 5 /* MPIDR */
and r0, r0, #0xf
mov pc, lr

Expand Down Expand Up @@ -635,15 +649,20 @@ START_POINT_END(_thread_start)
init_mtbl:
.space (4*4096) /* The L1 translation table therefore contains 4096 32-bit (word-sized) entries. */

/*
* void rt_hw_mmu_switch(rt_uint32_t* mmutable_p);
* r0 --> mmutable_p (mmu table address)
*/
.global rt_hw_mmu_switch
rt_hw_mmu_switch:
orr r0, #0x18
mcr p15, 0, r0, c2, c0, 0 // ttbr0
//invalid tlb
orr r0, #0x18 /* RGN=0b11 (Outer WB-WA) */
mcr p15, 0, r0, c2, c0, 0 /* TTBR0 */

/* invalidate TLB, I-cache and branch predictor */
mov r0, #0
mcr p15, 0, r0, c8, c7, 0
mcr p15, 0, r0, c7, c5, 0 //iciallu
mcr p15, 0, r0, c7, c5, 6 //bpiall
mcr p15, 0, r0, c8, c7, 0 /* ITLBIALL */
mcr p15, 0, r0, c7, c5, 0 /* ICIALLU */
mcr p15, 0, r0, c7, c5, 6 /* BPIALL */

dsb
isb
Expand All @@ -653,7 +672,7 @@ rt_hw_mmu_switch:
.global rt_hw_set_process_id
rt_hw_set_process_id:
LSL r0, r0, #8
MCR p15, 0, r0, c13, c0, 1
MCR p15, 0, r0, c13, c0, 1 /* CONTEXTIDR */
mov pc, lr


Expand Down