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MicroBlaze Processor Reference Guide
UG081 (v14.7)
Chapter 3:
MicroBlaze Signal Interface Description
FSL Transactions
FSL BUS Write Operation
A write to the FSL bus is performed by MicroBlaze using one of the put or putd instructions. A write
operation transfers the register contents to an output FSL bus. The transfer is completed in a single
clock cycle for blocking mode writes to the FSL (put and cput instructions) as long as the FSL FIFO
does not become full. If the FSL FIFO is full, the processor stalls until the FSL full flag is lowered.
The non-blocking instructions (with prefix n), always complete in a single clock cycle even if the
FSL was full. If the FSL was full, the write is inhibited and the carry bit is set in the MSR.
FSL BUS Read Operation
A read from the FSL bus is performed by MicroBlaze using one of the get or getd instructions. A
read operations transfers the contents of an input FSL to a general purpose register. The transfer is
typically completed in 2 clock cycles for blocking mode reads from the FSL as long as data exists in
the FSL FIFO. If the FSL FIFO is empty, the processor stalls at this instruction until the FSL exists
flag is set. In the non-blocking mode (instructions with prefix n), the transfer is completed in one or
two clock cycles irrespective of whether or not the FSL was empty. In the case the FSL was empty,
the transfer of data does not take place and the carry bit is set in the MSR.
Direct FSL Connections
A direct FSL connection can be used to avoid the need for the FSL bus. This can be useful in case
no buffering is needed between the two connected IP cores, since the FSL bus FIFO is not included
with a direct connection. No buffering reduces the communication latency and required
implementation resources.
Each of the MicroBlaze FSL interfaces can either use a direct FSL connection or an FSL bus.
A MicroBlaze DWFSL interface is the initiator on a direct FSL connection, which can only be
connected to a DWFSL target. The DWFSL initiator and target have exactly the same signal names,
identical to the MFSL signals, depicted in
. MicroBlaze uses the DWFSL interface to
write data to the target with one of the put or putd instructions.
A MicroBlaze DRFSL interface is the target on a direct FSL connection, which can only be
connected to a DRFSL initiator. The DRFSL initiator and target have exactly the same signal names,
identical to the SFSL signals, depicted in
. MicroBlaze uses the DRFSL interface to read
data from the initiator with one of the get or getd instructions.
The Xilinx CacheLink (XCL) interface is implemented with direct FSL connections.
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