IEEE Std 1212:2001 pdf free download

IEEE Std 1212:2001 pdf free download.IEEE Standard for a Control and Status Registers (CSR) Architecture for Microcomputer Buses.
NOTE—A swap command is not explicitly defined, since a mask_swap operation that specifies an arg value of all ones provides equivalent functionality.
Buses compliant with this standard shall define an encoding for the lock functions specified by Table 2 and sufficient to acconimodate 16 values: the specification of other lock functions numbered 1016 and higher is a bus-dependent option.
Some of the lock operations perform arithmetic operations: their operands are unsigned integers. Correct implementation of these operations requires knowledge of the relative significance of the bytes within the addressed data: these are denoted by the suffixes _big and _liuk. For operations suffixed with _big, the byte with the smallest offset within the addressed region is deemed the most significant while for operations suffixed with _link it is the least significant. Correct implementation of arithmetic operations also requires the applicable bus standard to specify an invariant mapping from bytes transferred over the bus to bytes in the node’s address space. The mapping is independent of the relative arithmetic significance of the bytes. The recommended mapping is for the first byte transferred over the bus to correspond to a zero byte offset within the addressed region and subseqLlent bytes to correspond 10 incrementing ofiscis ssithin the region.
When a lock transaction addresses a location that has one or more reserved bits or fields, the results are not necessarily obvious. Unless otherwise specified by the applicable bus standard, the behavior of a particular lock function shall be determined by applying rules for reserved fields in order, as follows:
a) The addressed location’s old value shall be obtained as if via a read request and shall be returned in the lock response: reserved fields are read as zeros:
b) An intermediate value shall be calculated according to the C code in Table 2 (this is not explicitly shown but is the right-hand part of each of the assignment statements in the table): and
C) The intermediate value shall be stored in the addressed location as if via a write request: reserved fields shall be ignored and remain zero in the location. The contents of the location after this operation are the net value.