Host Coalescing Control Registers
BCM5718 Programmer’s Guide
Broadcom
®
January 29, 2016 • 5718-PG108-R
Page 418
Send Max Coalesced BD Count Register (offset: 0x3C14)
This register contains the maximum number of send BDs that must be processed by the device before the
device will update the status block due to the transmission of packets. Whenever the device completes the DMA
of transmit packet buffer, it increments an internal send coalesce BD counter. When this internal counter reaches
the value in this register, a status block update will occur. This counter will be reset (i.e. zeroed) whenever a
status block update occurs regardless of the reason for the status block update. This register must be initialized
by host software. A value of 0 in this register disables the send max BD coalescing logic. In this case, status
block updates will occur for receive packets only via the Send Coalescing Ticks mechanism. Of course, status
block updates for other reasons (e.g., receive events) will also include any updates to the send indices. For
simplicity, if a host wanted to get a status block update for every transmitted packet, the host driver could just
set this register to a value of 1. On the other hand, by setting the value in this register to a high number, a
software device driver can reduce the number of status block updates and interrupts that occur due to
transmitting packets. This can increase performance in hosts that are under a high degree of stress and whose
RISCs are saturated due to handling a large number of interrupts from the network controller. However, in lower
traffic environments, there is no guarantee that consecutive packets will be transmitted in a timely manner.
Therefore, for those environments, it is recommended that the Send Coalescing Ticks register are used to make
sure that status block updates due to transmitting packets are not delayed for an infinite amount of time.
IOV + Multiple TXQ:
Send Max Coalesced BD Count Register for TXQ 0 => 0x3C14
Send Max Coalesced BD Count Register for TXQ 1 => 0x3D8C
Send Max Coalesced BD Count Register for TXQ 2 => 0x3DA4
Send Max Coalesced BD Count Register for TXQ 3 => 0x3DBC
Send Max Coalesced BD Count Register for TXQ 4 => 0x3DD4
Send Max Coalesced BD Count Register for TXQ 5 => 0x3DEC
Send Max Coalesced BD Count Register for TXQ 6 => 0x3E04
Send Max Coalesced BD Count Register for TXQ 7 => 0x3E1C
Send Max Coalesced BD Count Register for TXQ 8 => 0x3E34
Send Max Coalesced BD Count Register for TXQ 9 => 0x3E4C
Send Max Coalesced BD Count Register for TXQ 10 => 0x3E64
Send Max Coalesced BD Count Register for TXQ 11 => 0x3E7C
Send Max Coalesced BD Count Register for TXQ 12 => 0x3E94
Send Max Coalesced BD Count Register for TXQ 13 => 0x3EAC
Send Max Coalesced BD Count Register for TXQ 14 => 0x3EC4
Send Max Coalesced BD Count Register for TXQ 15 => 0x3EDC
Send Max Coalesced BD Count Register for TXQ 16 => 0x3EF4