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//! i.MX RT target support.
//!
//! Defines a `cortex-m-rt` pre-init function that disables watchdogs and initializes TCM.
//! It then copies instructions, read-only data, and the vector table to their intended location.
//! This only happens if LMAs and VMAs differ.
//!
//! There's a few behaviors worth mentioning:
//!
//! - The implementation never clears the INIT_xTCM_EN bits in GPR16 if the xTCM is unused.
//! The first reason is because we can't do this on the 1170 chips; the bits are reserved and
//! should always be set (guessing its for the CM4, which always uses TCM). The second reason
//! is that it doesn't seem necessary; we'll let xTCM initialize out of non-POR reset. From what
//! I could gather, this would be the case if we set fuse values to specify an all-OCRAM config,
//! and nothing says we need to flip these bits if the _fuses_ don't allocate xTCM. (Maybe this
//! automagically happens? Not sure.)
//! - We're not changing CM7_xTCMSZ to reflect the xTCM sizes. Again, the setting isn't available
//! on the 1170 chips. It's also OK to keep the POR value, since it represents the maximum-possible
//! TCM size. This means that users have finer control over xTCM memory sizes, but invalid xTCM accesses
//! won't cause a bus fault. See 3.1.3.2. in AN12077 for more discussion.
//!
//! Other notes:
//!
//! It's important that something sets the stack pointer. On the 10xx, the boot ROM sets the stack
//! pointer. But on the 11xx, the boot ROM doesn't set the stack pointer. See the link below for
//! more information. This implementation relies on the cortex-m-rt 0.7.2 "set-sp" feature to always
//! set the stack pointer, no matter the target chip.
//!
//! <https://community.nxp.com/t5/i-MX-RT/RT1176-ROM-code-does-not-set-stack-pointer-correctly/td-p/1388830>
use core::{arch::global_asm, ffi::c_void};
pub use cortex_m_rt::*;
global_asm! {r#"
.cfi_sections .debug_frame
.section .__pre_init,"ax"
.global __pre_init
.type __pre_init,%function
.thumb_func
.cfi_startproc
__pre_init:
ldr r0, =__imxrt_family @ Need to know which chip family we're initializing.
ldr r1, =1170
cmp r0, r1 @ Is this an 1170?
# Disable RTWODOG3.
ite eq
ldreq r2, =0x40038000 @ RTWDOG base address for 11xx chips...
ldrne r2, =0x400BC000 @ RTWDOG base address for 10xx chips...
ldr r3, =0xD928C520 @ RTWDOG magic number
str r3, [r2, #4] @ RTWDOG[CNT] = 0xD928C520.
ldr r3, [r2] @ r3 = RTWDOG[CS]
bic r3, r3, #1<<7 @ r3 = r3 & !(1 << 7), clears enable.
str r3, [r2] @ RTWDOG[CS] = r3
# Prepare FlexRAM regions.
ldr r0, =0x400AC000 @ IMXRT_IOMUXC_GPR base address for 10xx chips, overwritten if actually 11xx...
ldr r1, =__flexram_config @ Value for GPR17 (and GPR18 for 11xx)
itttt eq @ Need a few extra operations to handle 1170 split banks.
ldreq r0, =0x400E4000 @ IMXRT_IOMUXC_GPR base address for 11xx chips, overwrite 10xx address...
lsreq r2, r1, #16 @ r2 = ((unsigned)r1 >> 16)
streq r2, [r0, #72] @ *(IMXRT_IOMUXC_GPR + 18) = r2
ubfxeq r1, r1, #0, #16 @ r1 = ((unsigned)r1 >> 0) & 0xFFFF, overwrite r1 with lower halfword.
str r1, [r0, #68] @ *(IMXRT_IOMUXC_GPR + 17) = r1
ldr r1, [r0, #64] @ r1 = *(IMXRT_IOMUXC_GPR + 16)
orr r1, r1, #1<<2 @ r1 |= 1 << 2
str r1, [r0, #64] @ *(IMXRT_IOMUXC_GPR + 16) = r1
# Conditionally copy text.
ldr r0, =__stext
ldr r2, =__sitext
cmp r2, r0
beq 42f
ldr r1, =__etext
43:
cmp r1, r0
beq 42f
ldm r2!, {{r3}}
stm r0!, {{r3}}
b 43b
42:
# Conditionally copy the vector table.
ldr r0, =__svector_table
ldr r2, =__sivector_table
cmp r2, r0
beq 52f
ldr r1, =__evector_table
53:
cmp r1, r0
beq 52f
ldm r2!, {{r3}}
stm r0!, {{r3}}
b 53b
52:
# Conditionally copy read-only data.
ldr r0, =__srodata
ldr r2, =__sirodata
cmp r2, r0
beq 62f
ldr r1, =__erodata
63:
cmp r1, r0
beq 62f
ldm r2!, {{r3}}
stm r0!, {{r3}}
b 63b
62:
# All done; back to the reset handler.
bx lr
.cfi_endproc
.size __pre_init, . - __pre_init
"#
}
/// Returns a pointer to the end of the heap.
///
/// The returned pointer is guaranteed to be 4-byte aligned.
#[inline]
pub fn heap_end() -> *mut u32 {
extern "C" {
static mut __eheap: c_void;
}
unsafe { core::ptr::addr_of_mut!(__eheap) as _ }
}
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