Digi NS9215 Terms and abbreviations, Mnemonics for these instructions are, For reads, For writes

Terms and abbreviations

WO R K I N G W I T H T H E C P U

System control processor (CP15) registers

31	28	27 26		25	24 23		21	20 19		16 15		12	11 10		9	8	7	5	4	3	0
Cond		1	1	1	0	Opcode		L	CRn		Rd		1	1	1	1	Opcode		1		CRm
							_1											_2

Figure 1: CP15 MRC and MCR bit pattern

The mnemonics for these instructions are:

MCR{cond} p15,opcode_1,Rd,CRn,CRm,opcode_2

MRC{cond} p15,opcode_1,Rd,CRn,CRm,opcode_2

If you try to read from a write-only register or write to a read-only register, you will have UNPREDICTABLE results. In all instructions that access CP15:

The opcode_1 field SHOULD BE ZERO, except when the values specified are used to select the operations you want. Using other values results in unpredictable behavior.

The opcode_2 and CRm fields SHOULD BE ZERO, except when the values specified are used to select the behavior you want. Using other values results in unpredictable behavior.

This table lists the terms and abbreviations used in the CP15 registers and explanations.

Term	Abbreviation	Description
		For reads:
UNPREDICTABLE	UNP
		The data returned when reading from this location is
		unpredictable, and can have any value.
		For writes:
		Writing to this location causes unpredictable
		behavior, or an unpredictable change in device
		configuration.
UNDEFINED	UND	An instruction that accesses CP15 in the manner
		indicated takes the UNDEFINED instruction
		exception.
SHOULD BE ZERO	SBZ	When writing to this field, all bits of the field
		SHOULD BE ZERO.
SHOULD BE ONE	SBO	When writing to this location, all bits in this field
		SHOULD BE ONE.
SHOULD BE ZERO or	SBZP	When writing to this location, all bits of this field
PRESERVED		SHOULD BE ZERO or PRESERVED by writing the
		same value that has been read previously from the
		same field.

84Hardware Reference NS9215