GR740-UM-DS, Nov 2017, Version 1.7
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GR740
13.4
AMBA ports
The AMBA ports are Cobham Gaisler’s GRSPW2 controller with the SpaceWire codec removed.
Thus, the same drivers that are provided for the GRSPW2 can also be used for an AMBA port of the
router. Only one additional driver is needed, which handles the setup of the registers within the con-
figuration port.
13.4.1 Overview
The router’s AMBA ports are configured by register accesses through an APB interface. Data is trans-
ferred through one to four DMA channels using an AHB master interface.
13.4.2 Operation
The main sub-blocks of the router AHB interfaces are the DMA engines, the RMAP target and the
AMBA interface. A block diagram of the internal structure can be found in Figure 13.
The AMBA interface is divided into the AHB master interface and the APB interface. The DMA
engines have FIFO interfaces to the router switch matrix. These FIFOs are used to transfer N-Chars
between the AMBA bus and the other ports in the router.
The RMAP target handles incoming packets, which are determined to be RMAP commands instead of
the receiver DMA engine. The RMAP command is decoded and if it is valid the operation is per-
formed on the AHB bus. If a reply was requested, it is automatically transmitted back to the source by
the RMAP transmitter.
The AMBA ports are controlled by writing to a set of user registers through the APB interface and a
set of signals. The different sub-modules are discussed in further detail in later sections.
13.4.2.1 Protocol support
The AMBA port only accepts packets with a valid destination address in the first received byte. Pack-
ets with address mismatch will be silently discarded (except in promiscuous mode which is covered in
section 13.4.4.10).
The second byte is sometimes interpreted as a protocol ID as described hereafter. The RMAP protocol
(ID=0x1) is the only protocol handled separately in hardware while other packets are stored to a DMA
channel. If the RMAP target is enabled, all RMAP commands will be processed, executed and
answered automatically in hardware. Otherwise, RMAP commands are stored to a DMA channel in
the same way as other packets. RMAP replies are always stored to a DMA channel. More information
on the RMAP protocol support is found in section 13.4.6 (note that this RMAP target is different from
Figure 13.
Block diagram of the Router DMA port
TRANSMITTER
FSM
SEND
RMAP
FSM
TRANSMITTER
DMA ENGINE
RECEIVER
DMA ENGINE
TRANSMITTER
RMAP
RECEIVER
N-CHAR
FIFO
RECEIVER
AHB FIFO
RECEIVER DATA
PARALLELIZATION
AHB
MASTER INTERFACE
REGISTERS
APB
INTERFACE
FROM ROUTER
SWITCH MATRIX
TO ROUTER
SWITCH MATRIX