NXP Semiconductors KL25 Series - Page 281

17.4.2 BME Decorated Loads
The functions supported by the BME's decorated loads include two single-bit load-and-
{set, clear} operators plus unsigned bit field extracts. For the two load-and-{set, clear}
operations, BME converts a single decorated AHB load transaction into a 2-cycle atomic
read-modify-write sequence, where the combined read-modify operations are performed
in the first AHB data phase, and then the write is performed in the second AHB data
phase as the original read data is returned to the processor core. For an unsigned bit field
extract, the decorated load transaction is stalled for one cycle in the BME as the data field
is extracted, then aligned and returned to the processor in the 2nd AHB data phase. This
is the only decorated transaction that is not an atomic read-modify-write, as it is a simple
data read.
A generic timing diagram of a decorated load showing a load-and-set 1-bit operation is
shown as follows.
x x+1 x+2 x+3
next
4c.v_wxyz
next
next
400v_wxyz 400v_wxyz
next
next
4c.v_wxyz
rdata + 1bit
rdata + 1bit
next
rdata
orig_1bit
CYCLE RULER
hclk
BME AHB Input Bus
mx_haddr
mx_hattr
mx_hwrite
mx_hwdata
mx_hrdata
mx_hready
BME AHB Output Bus
sx_haddr
sx_hattr
sx_hwrite
sx_hwdata
sx_hrdata
sx_hready
BME States + Datapath
control_state_dp1
control_state_dp2
reg_addr_data_dp
Figure 17-7. Decorated load: load-and-set 1-bit field insert timing diagram
Decorated load-and-{set, clear} 1-bit operations follow the execution template shown in
the above figure: a 2-cycle read-modify-write operation:
Chapter 17 Bit Manipulation Engine (BME)
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 281