ARM Cortex M4/M7 optimized memory operations

Implementation Description:

This assembly code implements optimized versions of the memcmp, memset, and memcpy functions for the ARM architecture, utilizing the ARMv7-M architecture with VFPv2 floating-point support. It's applicable for Cortex M4 and Cortex M7 MCU's. These functions are commonly used for memory comparison, setting, and copying, respectively, and the use of VFP instructions enhances performance.

Functionality and Function Descriptions:

1. memcmp_vfp:

   • Purpose: Compares two blocks of memory.
   • Registers:
     • r0: Pointer to the first memory block.
     • r1: Pointer to the second memory block.
     • r2: Number of bytes to compare.
   • Operation:
     • If r2 (size) is zero, returns 0 indicating the blocks are equal.
     • Compares memory in 4-byte chunks using ldr and subs instructions.
     • Falls back to comparing 1-byte chunks if less than 4 bytes remain.
     • If any mismatch is found, returns -1; otherwise, returns 0.

2. memset_vfp:

   • Purpose: Fills a block of memory with a specified value.
   • Registers:
     • r0: Pointer to the memory block.
     • r1: Value to be set.
     • r2: Number of bytes to set.
   • Operation:
     • If r2 (size) is zero, terminates the function.
     • Prepares the d0 register with the value to be set using bfi and vmov instructions.
     • Sets memory in 32-byte chunks using vstr instructions.
     • Falls back to setting 8-byte, 4-byte, and 1-byte chunks as the size decreases.
     • Returns to the caller using bx lr.

3. memcpy_vfp:

   • Purpose: Copies a block of memory from a source to a destination.
   • Registers:
     • r0: Pointer to the destination memory block.
     • r1: Pointer to the source memory block.
     • r2: Number of bytes to copy.
   • Operation:
     • If r2 (size) is zero, terminates the function.
     • Copies memory in 128-byte chunks using vldr and vstr instructions.
     • Falls back to copying 32-byte, 8-byte, 4-byte, and 1-byte chunks as the size decreases.
     • Returns the address of the destination buffer using mov and bx lr.

Detailed Function Operations:

1. memcmp_vfp:

   • Start: Checks if r2 is zero and jumps to _cmp_good if true. Otherwise, compares memory in 4-byte chunks.
   • 4-Byte Comparison Loop (_cmp4): Loads and compares 4 bytes from each memory block. If they are not equal, jumps to _cmp_err. Otherwise, decrements r2 and repeats until less than 4 bytes remain.
   • 1-Byte Comparison Loop (_cmp1): Loads and compares 1 byte from each memory block. If they are not equal, jumps to _cmp_err. Otherwise, decrements r2 and repeats until no bytes remain.
   • End: If all comparisons are successful, moves 0 into r0 and returns. If any comparison fails, moves -1 into r0 and returns.

2. memset_vfp:

   • Start: Checks if r2 is zero and jumps to stop if true. Prepares the d0 register with the value to be set.
   • 32-Byte Setting Loop (set32): Sets 32 bytes of memory at a time using vstr instructions. Adjusts r0 and r2 accordingly and repeats until less than 32 bytes remain.
   • 8-Byte Setting Loop (set8): Sets 8 bytes of memory at a time using vstr instructions. Adjusts r0 and r2 accordingly and repeats until less than 8 bytes remain.
   • 4-Byte Setting Loop (set4): Sets 4 bytes of memory at a time using str instructions. Adjusts r0 and r2 accordingly and repeats until less than 4 bytes remain.
   • 1-Byte Setting Loop (set1): Sets 1 byte of memory at a time using strb instructions. Adjusts r0 and r2 accordingly and repeats until no bytes remain.
   • End: Restores the original values of d0 and r1 from the stack and returns to the caller using bx lr.

3. memcpy_vfp:

   • Start: Checks if r2 is zero and jumps to stop if true. Pushes the source pointer onto the stack and prepares the d0 register.
   • 128-Byte Copy Loop (copy128): Copies 128 bytes of memory at a time using vldr and vstr instructions. Adjusts r0, r1, and r2 accordingly and repeats until less than 128 bytes remain.
   • 32-Byte Copy Loop (copy32): Copies 32 bytes of memory at a time using ldr and str instructions. Adjusts r0, r1, and r2 accordingly and repeats until less than 32 bytes remain.
   • 8-Byte Copy Loop (copy8): Copies 8 bytes of memory at a time using ldr and str instructions. Adjusts r0, r1, and r2 accordingly and repeats until less than 8 bytes remain.
   • 4-Byte Copy Loop (copy4): Copies 4 bytes of memory at a time using ldr and str instructions. Adjusts r0, r1, and r2 accordingly and repeats until less than 4 bytes remain.
   • 1-Byte Copy Loop (copybytes): Copies 1 byte of memory at a time using ldrb and strb instructions. Adjusts r0, r1, and r2 accordingly and repeats until no bytes remain.
   • End: Restores the original values of d0 and r1 from the stack, moves the address of the destination buffer into r0, and returns to the caller using bx lr.

libmemory_operations_release_imxrt1050.a memory statistics: