Table 17-3. Cycle definitions of decorated store: logical XOR
Pipeline Stage Cycle
x x+1 x+2
BME AHB_ap Forward addr to memory;
Decode decoration; Convert
master_wt to slave_rd;
Capture address, attributes
Recirculate captured addr +
attr to memory as slave_wt
<next>
BME AHB_dp
<previous>
Perform memory read; Form
(rdata ^ wdata) and capture
destination data in register
Perform write sending
registered data to memory
17.4.1.4 Decorated Store Bit Field Insert (BFI)
This command inserts a bit field contained in the write data operand, defined by LSB
position (b) and the bit field width (w+1), into the memory "container" defined by the
access size associated with the store instruction using an atomic read-modify-write
sequence.
The data size is specified by the write operation and can be byte (8-bit), halfword (16-bit)
or word (32-bit). Note for the word sized operation, the maximum bit field width is 16
bits. The core performs the required write data lane replication on byte and halfword
transfers.
The BFI operation can be used to insert a single bit into a peripheral. For this case, the w
field is simply set to 0, indicating a bit field width of 1.
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
iobfib 0 1 0 1 - - b b b - w w w mem_addr
iobfih
0 1 0 1 - b b b b w w w w mem_addr 0
iobfiw
0 1 0 1 b b b b b w w w w mem_addr 0 0
Figure 17-6. Decorated address store: bit field insert
where addr[28] = 1 signals a BFI operation, addr[27:23] is "b", the LSB identifier,
addr[22:19] is "w", the bit field width minus 1 identifier, and addr[18:0] specifies the
address offset into the peripheral space based at 0x4000_0000. The "-" indicates an
address bit "don't care". Note, unlike the other decorated store operations, BFI uses
addr[19] as the least significant bit in the "w" specifier and not as an address bit.
The decorated BFI write operation is defined in the following pseudo-code as:
iobfi<sz>(accessAddress, wdata) // decorated bit field insert
tmp = mem[accessAddress & 0xE007FFFF, size] // memory read
mask = ((1 << (w+1)) - 1) << b // generate bit mask
Chapter 17 Bit Manipulation Engine (BME)
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 279
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