1 files changed, 147 insertions, 0 deletions
diff --git a/src/target.rs b/src/target.rs
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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.
+
+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
+
+    # Set the stack pointer.
+    #
+    # This is particularly important for the 11xx. Its boot ROM
+    # doesn't take this step before it calls into our reset
+    # handler. The 10xx boot ROM handles this differently.
+    # Also noted in
+    # https://community.nxp.com/t5/i-MX-RT/RT1176-ROM-code-does-not-set-stack-pointer-correctly/td-p/1388830
+    #
+    # If this feature is published in a future cortex-m-rt version,
+    # we could remove this. See below for VTOR, too.
+    #
+    # Shouldn't matter where we perform this within this function.
+    # We're assuming that the caller isn't using the stack.
+    ldr r0, =__sstack
+    msr msp, r0
+
+    # 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:
+
+    # Set VTOR. If this feature is published in a future cortex-m-rt version,
+    # we could remove this.
+    ldr r0, =0xE000ED08
+    ldr r1, =__svector_table
+    str r1, [r0]
+    dsb
+    isb
+
+    # 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 _ }
+}