1 files changed, 73 insertions, 0 deletions
diff --git a/src/host/imxrt-boot-header.x b/src/host/imxrt-boot-header.x
new file mode 100644
index 0000000..67355a2
--- /dev/null
+++ b/src/host/imxrt-boot-header.x
@@ -0,0 +1,73 @@
+/* This extra file is injected into imxrt-memory.x depending on the
+ * runtime configuration.
+ */
+
+/* If you're ever playing with the boot ROM copy, this is your image size.
+ *
+ * Note that it depends on the section layout! Need to represent contiguous
+ * sections starting from the boot header.
+ */
+__image_size = SIZEOF(.boot) + SIZEOF(.vector_table) + SIZEOF(.text) + SIZEOF(.rodata);
+
+/* END TODO */
+EXTERN(FLEXSPI_CONFIGURATION_BLOCK);
+
+/* # Sections */
+SECTIONS
+{
+  /* Boot header for serial NOR FlexSPI XIP.
+   *
+   * It's 'XIP' in that it starts executing instructions
+   * from flash immediately out of reset. The runtime then
+   * manually copies instructions (data, etc.), and we jump
+   * to that. After that jump, we're no longer XIP.
+   *
+   * The i.MX RT boot ROM also supports a way to copy the
+   * application image by changing the boot data configuration.
+   * Specifically, point the 'start of image' to somewhere other
+   * than the start of flash, and specify how many bytes to copy.
+   * The boot ROM copies the image, then jumps to the vector table.
+   * There's a catch: the boot ROM copies the first 8K from the
+   * start of flash too. This represents the entire boot header,
+   * including the FCB, IVT, and boot data. (NXP docs say that the
+   * initial load region is 4K; my testing shows that it's 8K, and
+   * this aligns with observations of others.) If you ever want to
+   * try this, make sure you're specifing the VMA and LMA of the
+   * boot head section to represent this 8K relocation.
+   */
+  .boot ORIGIN(FLASH):
+  {
+    . += __fcb_offset;          /* Changes based on the chip */
+    KEEP(*(.fcb));
+    . = ORIGIN(FLASH) + 0x1000;
+    /* ------------------
+     * Image vector table
+     * ------------------
+     *
+     * Not to be confused with the ARM vector table. This tells the boot ROM
+     * where to find the boot data and (eventual) first vector table.
+     * The IVT needs to reside right here.
+     */
+    __ivt = .;
+    LONG(0x402000D1);           /* Header, magic number */
+    LONG(__sivector_table);     /* Address of the vectors table */
+    LONG(0x00000000);           /* RESERVED */
+    LONG(0x00000000);           /* Device Configuration Data (unused) */
+    LONG(__boot_data);          /* Address to boot data */
+    LONG(__ivt);                /* Self reference */
+    LONG(0x00000000);           /* Command Sequence File (unused) */
+    LONG(0x00000000);           /* RESERVED */
+    /* ---------
+      * Boot data
+      * ---------
+      */
+    __boot_data = .;
+    LONG(ORIGIN(FLASH));        /* Start of image */
+    LONG(__image_size);         /* Length of image */
+    LONG(0x00000000);           /* Plugin flag (unused) */
+    LONG(0xDEADBEEF);           /* Dummy to align boot data to 16 bytes */
+    *(.Reset);                  /* Jam the imxrt-rt reset handler into flash. */
+    *(.__pre_init);             /* Also jam the pre-init function, since we need it to run before instructions are placed. */
+    . = ORIGIN(FLASH) + 0x2000;   /* Reserve the remaining 8K as a convenience for a non-XIP boot. */
+  } > FLASH
+}