• Cycle x+1, 1st AHB data phase: A bit mask is generated based on the starting bit
position and the field width; the mask is AND'ed with the memory read data to
isolate the bit field; the resulting data is captured in a data register; the input bus
cycle is stalled
• Cycle x+2, 2nd AHB data phase: Registered data is logically right-aligned for proper
alignment and driven onto the input read data bus
NOTE
Any wait states inserted by the slave device are simply passed
through the BME back to the master input bus, stalling the
AHB transaction cycle for cycle.
42.3.2.1 Decorated load: load-and-clear 1 bit (LAC1)
This command loads a 1-bit field defined by the LSB position (b) into the core's general
purpose destination register (Rt) and zeroes the bit in the memory space after performing
an atomic read-modify-write sequence.
The extracted 1-bit data field from the memory address is right-justified and zero-filled in
the operand returned to the core.
The data size is specified by the read operation and can be byte (8-bit), halfword (16-bit)
or word (32-bit).
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
0 *
*
0 1 0
-
-
b b b
-
mem_addr
0 *
*
0 1 0
-
b b b b
-
mem_addr
0
0 *
*
0 1 0 b b b b b
-
mem_addr
0 0
iolaclb
iolaclh
iolaclw
Figure 42-9. Decorated load address: load-and-clear 1 bit
See
, where addr[30:29] = 10 for peripheral, addr[28:26] = 010 specifies the
load-and-clear 1 bit operation, addr[25:21] is "b", the bit identifier, and mem_addr[19:0]
specifies the address offset into the space based at 0x4000_0000 for peripheral. The "-"
indicates an address bit "don't care".
The decorated load-and-clear 1-bit read operation is defined in the following pseudo-code
as:
rdata = iolac1<sz>(accessAddress) // decorated load-and-clear 1
tmp = mem[accessAddress & 0xE00FFFFF, size] // memory read
mask = 1 << b // generate bit mask
rdata = (tmp & mask) >> b // read data returned to core
tmp = tmp & ~mask // modify
mem[accessAddress & 0xE00FFFFF, size] = tmp // memory write
Functional description
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
844
Freescale Semiconductor, Inc.
