doc: add man-page for cmp command

Provide a man-page for the cmp command.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

doc/usage/cmd/cmp.rst

@@ -0,0 +1,105 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+cmp command
+===========
+
+Synopsis
+--------
+
+::
+
+    cmp [.b, .w, .l, .q] addr1 addr2 count
+
+Description
+-----------
+
+The cmp command is used to compare two memory areas. By default it works on
+four byte tuples. By appending .b, .w, .l, .q the size of the tuples is
+controlled:
+
+cmp.b
+    compare 1 byte tuples
+
+cmp.w
+    compare 2 byte tuples
+
+cmp.l
+    compare 4 byte tuples
+
+cmp.q
+    compare 8 byte tuples
+
+The parameters are used as follows:
+
+addr1
+    Address of the first memory area.
+
+addr2
+    Address of the second memory area.
+
+count
+    Number of bytes to compare (as hexadecimal number).
+
+Example
+-------
+
+In the example below the strings "Hello world\n" and "Hello World\n" are written
+to memory and then compared.
+
+::
+
+    => mm.b 0x1000000
+    01000000: 00 ? 48
+    01000001: 00 ? 65
+    01000002: 00 ? 6c
+    01000003: 00 ? 6c
+    01000004: 00 ? 6f
+    01000005: 00 ? 20
+    01000006: 00 ? 77
+    01000007: 00 ? 6f
+    01000008: 00 ? 72
+    01000009: 00 ? 6c
+    0100000a: 00 ? 64
+    0100000b: 00 ? 0d
+    0100000c: 00 ? => <INTERRUPT>
+    => mm.b 0x101000
+    00101000: 00 ? 48
+    00101001: 00 ? 65
+    00101002: 00 ? 6c
+    00101003: 00 ? 6c
+    00101004: 00 ? 6f
+    00101005: 00 ? 20
+    00101006: 00 ? 57
+    00101007: 00 ? 6f
+    00101008: 00 ? 72
+    00101009: 00 ? 6c
+    0010100a: 00 ? 64
+    0010100b: 00 ? 0d
+    0010100c: 00 ? => <INTERRUPT>
+    => cmp 0x1000000 0x101000 0xc
+    word at 0x01000004 (0x6f77206f) != word at 0x00101004 (0x6f57206f)
+    Total of 1 word(s) were the same
+    => cmp.b 0x1000000 0x101000 0xc
+    byte at 0x01000006 (0x77) != byte at 0x00101006 (0x57)
+    Total of 6 byte(s) were the same
+    => cmp.w 0x1000000 0x101000 0xc
+    halfword at 0x01000006 (0x6f77) != halfword at 0x00101006 (0x6f57)
+    Total of 3 halfword(s) were the same
+    => cmp.l 0x1000000 0x101000 0xc
+    word at 0x01000004 (0x6f77206f) != word at 0x00101004 (0x6f57206f)
+    Total of 1 word(s) were the same
+    => cmp.q 0x1000000 0x101000 0xc
+    double word at 0x01000000 (0x6f77206f6c6c6548) != double word at 0x00101000 (0x6f57206f6c6c6548)
+    Total of 0 double word(s) were the same
+
+Configuration
+-------------
+
+The cmp command is only available if CONFIG_CMD_MEMORY=y. The cmp.q command is
+only available if additionally CONFIG_MEM_SUPPORT_64BIT_DATA=y.
+
+Return value
+------------
+
+The return value $? is true (0) if the compared memory areas are equal.
+The reutrn value is false (1) if the compared memory areas differ.

doc/usage/index.rst

@@ -35,6 +35,7 @@ Shell commands
    cmd/cat
    cmd/cbsysinfo
    cmd/cls
+   cmd/cmp
    cmd/conitrace
    cmd/cyclic
    cmd/dm