CGEM(4)

NAME
cgem - Cadence GEM Gigabit Ethernet driver

SYNOPSIS
To compile this driver into the kernel, place the following lines in your kernel configuration file:

device ether
device miibus
device cgem

DESCRIPTION
The cgem driver provides support for the Cadence GEM (Gigabit Ethernet MAC). The Cadence GEM is used in some SoC (System on a Chip) devices such as the Xilinx Zynq-7000, the Xilinx Zynq UltraScale+, and the SiFive HiFive Unleashed.

The cgem driver supports the following media types:

autoselect
    Enable autoselection of the media type and options. The user can manually override the autoselected mode using ifconfig(8) or by adding media options to rc.conf(5).

10baseT/UTP
    Set 10Mbps operation. The ifconfig(8) mediaopt option can also be used to select either full-duplex or half-duplex modes.

100baseTX
    Set 100Mbps (Fast Ethernet) operation. The ifconfig(8) mediaopt option can also be used to select either full-duplex or half-duplex modes.

1000baseT
    Set 1000Mbps (Gigabit Ethernet) operation over twisted pair. The GEM supports 1000Mbps in full-duplex mode only.

The cgem driver supports the following media options:

full-duplex
    Force full-duplex operation.

half-duplex
    Force half-duplex operation.

The driver provides support for TCP/UDP/IP checksum offloading (although disabled by default). The device and driver also support 1536-byte frames for VLANs (vlanmtu).

SYSCTL VARIABLES
The following variables are available as both sysctl(8) variables and loader(8) tunables:

dev.cgem.%d.rxbufs
    The number of receive buffers allocated to the hardware. The default value is 256. The maximum value is 511. If this number is increased while the interface is UP, it will not take effect until the next packet is received. If this number is decreased while the interface is UP, buffers will not be immediately removed from the receive buffer ring but the number of buffers will decrease as packets are received until it reaches the new value.

dev.cgem.%d.rxhangwar
    This tunable enables a work-around to recover from receive hangs. The default value is 1. Set to 0 to disable the work-around.

The following read-only variables are available as sysctl(8) variables:

dev.cgem.%d._rxoverruns
    This variable counts the number of receive packet buffer overrun interrupts.

dev.cgem.%d._rxnobufs
    This variable counts the number of interrupts due to the GEM buffer ring going empty.

dev.cgem.%d._rxdmamapfails
    This variable is the number of times bus_dmamap_load_mbuf_sg(9) failed in the receive path.

dev.cgem.%d._txfull
    The number of times the GEM's transmit ring was full.

dev.cgem.%d._txdmamapfails
    This variable is the number of times bus_dmamap_load_mbuf_sg(9) failed in the transmit path.

dev.cgem.%d._txdefrags
    This variable is the number of times the driver needed to call m_defrag(9) because a packet queued for transmit had too many DMA segments.

dev.cgem.%d._txdefragfails
    This variable is the number of times m_defrag(9) failed.

dev.cgem.%d.stats.*
    The following variables are useful MAC counters supplied by the hardware:

dev.cgem.%d.stats.tx_bytes
    A 64-bit counter of the number of bytes transmitted in frames without error.

dev.cgem.%d.stats.tx_frames
    Counter of frames transmitted without error excluding pause frames.

dev.cgem.%d.stats.tx_frames_bcast
    Counter of broadcast frames transmitted without error excluding pause frames.

dev.cgem.%d.stats.tx_frames_multi
    Counter of multicast frames transmitted without error excluding pause frames.

dev.cgem.%d.stats.tx_frames_pause
    Counter of pause frames transmitted without error.

dev.cgem.%d.stats.tx_frames_64b
    Counter of 64 byte frames transmitted without error.

dev.cgem.%d.stats.tx_frames_65to127b
    Counter of 65 to 127 byte frames transmitted without error.

dev.cgem.%d.stats.tx_frames_128to255b
    Counter of 128 to 255 byte frames transmitted without error.

dev.cgem.%d.stats.tx_frames_256to511b
    Counter of 256 to 511 byte frames transmitted without error.

dev.cgem.%d.stats.tx_frames_512to1023b
    Counter of 512 to 1023 byte frames transmitted without error.

dev.cgem.%d.stats.tx_frames_1024to1536b
    Counter of 1024 to 1536 byte frames transmitted without error.

dev.cgem.%d.stats.tx_under_runs
    Counter of frames not transmitted due to a transmit underrun.

dev.cgem.%d.stats.tx_single_collisn
    Counter of frames experiencing a single collision before being successfully transmitted.

dev.cgem.%d.stats.tx_multi_collisn
    Counter of frames experiencing between 2 and 15 collisions before being successfully transmitted.

dev.cgem.%d.stats.tx_excsv_collisn
    Counter of frames that failed to transmit because they experienced 16 collisions.

dev.cgem.%d.stats.tx_late_collisn
    Counter of frames that experienced a late collision.

dev.cgem.%d.stats.tx_deferred_frames
    Counter of frames experiencing deferral due to carrier sense being active on their first attempt at transmission.

dev.cgem.%d.stats.tx_carrier_sense_errs
    Counter of frames transmitted where carrier sense was not seen during transmission or where carrier sense was deasserted after being asserted in a transmit frame without collision.

dev.cgem.%d.stats.rx_bytes
    A 64-bit counter of bytes received without error excluding pause frames.

dev.cgem.%d.stats.rx_frames
    Counter of frames received without error excluding pause frames.

dev.cgem.%d.stats.rx_frames_bcast
    Counter of broadcast frames receive without error excluding pause frames.

dev.cgem.%d.stats.rx_frames_multi
    Counter of multicast frames receive without error excluding pause frames.

dev.cgem.%d.stats.rx_frames_pause
    Counter of pause frames recevied without error.

dev.cgem.%d.stats.rx_frames_64b
    Counter of 64-byte frames received without error.

dev.cgem.%d.stats.rx_frames_65to127b
    Counter of 65 to 127 byte frames received without error.

dev.cgem.%d.stats.rx_frames_128to255b
    Counter of 128 to 255 byte frames received without error.

dev.cgem.%d.stats.rx_frames_256to511b
    Counter of 256 to 511 byte frames received without error.

dev.cgem.%d.stats.rx_frames_512to1023b
    Counter of 512 to 1023 byte frames received without error.

dev.cgem.%d.stats.rx_frames_1024to1536b
    Counter of 1024 to 1536 byte frames received without error.

dev.cgem.%d.stats.rx_frames_undersize
    Counter of frames received less than 64 bytes in length that do not also have either a CRC error or an alignment error.

dev.cgem.%d.stats.rx_frames_oversize
    Counter of frames received exceeding 1536 bytes and do not also have either a CRC error or an alignment error.

dev.cgem.%d.stats.rx_frames_jabber
    Counter of frames received exceeding 1536 bytes and also have either a CRC error, an alignment error, or a receive symbol error.

dev.cgem.%d.stats.rx_frames_fcs_errs
    Counter of frames received with a bad CRC and are between 64 and 1536 bytes.

dev.cgem.%d.stats.rx_frames_length_errs
    Counter of frames received that are shorter than that extracted from the length field.

dev.cgem.%d.stats.rx_symbol_errs
    Counter of receive symbol errors.

dev.cgem.%d.stats.rx_align_errs
    Counter of received frames that are not an integral number of bytes.

dev.cgem.%d.stats.rx_resource_errs
    Counter of frames successfully receive by the MAC but could not be copied to memory because no receive buffer was available.

dev.cgem.%d.stats.rx_overrun_errs
    Counter of frames that are address recognized but were not copied to memory due to a receive overrun.

dev.cgem.%d.stats.rx_frames_ip_hdr_csum_errs
    Counter of frames discarded due to an incorrect IP header checksum when checksum offloading is enabled.

dev.cgem.%d.stats.rx_frames_tcp_csum_errs
    Counter of frames discarded due to an incorrect TCP checksum when checksum offloading is enabled.

dev.cgem.%d.stats.rx_frames_udp_csum_errs
    Counter of frames discarded due to an incorrect UDP checksum when checksum offloading is enabled.

SEE ALSO
miibus(4), ifconfig(8) Zynq-7000 SoC Technical Reference Manual (Xilinx doc UG585), http://www.xilinx.com/support/documentation/user_guides/ug585-Zynq-7000-TRM.pdf.

HISTORY
The cgem device driver first appeared in FreeBSD 10.0.

AUTHORS
The cgem driver and this manual page was written by Thomas Skibo <thomasskibo@yahoo.com>.

BUGS
The GEM can perform TCP/UDP/IP checksum offloading. However, when transmit checksum offloading is enabled, the GEM generates and replaces checksums for all packets it transmits. In a system that is forwarding packets, the device could potentially correct the checksum of packet that was corrupted in transit. For this reason, checksum offloading is disabled by default but can be enabled using ifconfig(8).

When receive checksum offloading is enabled, the device will discard packets with bad TCP/UDP/IP checksums. The bad packets will not be counted in any netstat(1) statistics. There are sysctl(8) variables that count packets discarded by the hardware (see below).

The GEM used in the Zynq-7000 has a bug such that the receiver can potentially freeze up under a high load. The issue is described in sec. 16.7 "Known Issues" of the Zynq-7000 SoC Technical Reference Manual (Xilinx UG585 v1.7). The cgem driver implements the work-around suggested in the manual. It is believed that the bug does not exist in the Zynq UltraScale+ and SiFive SoCs so the work-around is disabled in those instances and enabled in all others. The work-around can be disabled by setting the dev.cgem.%d.rxhangwar sysctl(8) variable to 0.