docs: Add reference for Thumb2 inline assembler.

Thanks to Peter Hinch for contributing this.

1 files changed, 23 insertions, 0 deletions

diff --git a/docs/reference/asm_thumb2_ldr.rst b/docs/reference/asm_thumb2_ldr.rst
new file mode 100644
index 0000000000..16b7729592
--- /dev/null
+++ b/docs/reference/asm_thumb2_ldr.rst
@@ -0,0 +1,23 @@
+Load register from memory
+=========================
+
+Document conventions
+--------------------
+
+Notation: ``Rt, Rn`` denote ARM registers R0-R7 except where stated. ``immN`` represents an immediate
+value having a width of N bits hence ``imm5`` is constrained to the range 0-31. ``[Rn + immN]`` is the contents
+of the memory address obtained by adding Rn and the offset ``immN``. Offsets are measured in
+bytes. These instructions affect the condition flags.
+
+Register Load
+-------------
+
+* ldr(Rt, [Rn, imm7]) ``Rt = [Rn + imm7]`` Load a 32 bit word
+* ldrb(Rt, [Rn, imm5]) ``Rt = [Rn + imm5]`` Load a byte
+* ldrh(Rt, [Rn, imm6]) ``Rt = [Rn + imm6]`` Load a 16 bit half word
+
+Where a byte or half word is loaded, it is zero-extended to 32 bits.
+
+The specified immediate offsets are measured in bytes. Hence in the case of ``ldr`` the 7 bit value
+enables 32 bit word aligned values to be accessed with a maximum offset of 31 words. In the case of ``ldrh`` the
+6 bit value enables 16 bit half-word aligned values to be accessed with a maximum offset of 31 half-words.