The namespace PoC.misc.gearbox offers gearbox implementations with different
interfaces.
A gearbox is a bus interface converter, that resizes an input stream of
INPUT_BITS to an output stream of OUTPUT_BITS, while maintaining a constant
transfer rate. There are two kinds of gearboxes: down-scaling and up-scaling.
Gearboxes with common clock (cc) interface ... TODO
Gearbox use case:
- TODO
Gearboxes with full transfer rate preservation use a dependent clock (dc)
interface. For example a 32:8 gearbox_down_dc with an input frequency of 75 MHz
requires an output frequency of 300 MHz, because the scaling factor is 4. The
clocks MUST be multiples of each other and have a FIXED phase difference.
Gearbox use case:
- A SATA 3,0 Gbps controller uses an embedded multi-gigabit transceiver (MGT) in an FPGA to transmit and receive 300 MBps. The MGT interface is configured as a byte interface at 300 MHz. The link layer protocol works on 32 bit words. A gearbox_up_dc is used to pack 4 bytes into one 32 bit SATA word at a frequency of 75 MHz.
FIFO use case:
- GigabitEthernet (1GbE) uses a byte interface at 125 MHz. After processing MAC,
IP and UDP packets an overhead of 10 % is expected. Due to the application a
max link utilisation of 80% is excepted resulting in an effective datarate of
1 byte at 100 MHz. A
fifo_ic_gotis used to convert between the clock domains.