SPRZ450B February 2018 – September 2024 DRA74P , DRA75P , DRA76P , DRA77P
RGMII Clocks Should Be Enabled at Boot Time
Medium
The RGMII 1000 Mbps Transmit timing is based on the output clock (rgmiin_txc) being driven relative to the rising edge of an internal clock and the output control/data (rgmiin_txctl/txd) being driven relative to the falling edge of an internal clock source. If the internal clock source is allowed to be static low (i.e., disabled) for an extended period of time then when the clock is actually enabled the timing delta between the rising edge and falling edge can change over the lifetime of the device. This can result in the device switching characteristics degrading over time, and eventually failing to meet the Data Manual Delay Time/Skew specs.
To maintain RGMII 1000 Mbps IO Timings, SW should minimize the duration that the Ethernet internal clock source is disabled. Note that the device reset state for the Ethernet clock is "disabled".
Other RGMII modes (10 Mbps, 100Mbps) are not affected.
If the SoC Ethernet interface(s) are used in RGMII mode at 1000 Mbps, SW should minimize the time the Ethernet internal clock source is disabled to a maximum of 200 hours in a device life cycle. This is done by enabling the clock as early as possible in IPL (QNX) or SPL/u-boot (Linux/Android) by setting the register CM_GMAC_CLKSTCTRL[1:0]CLKTRCTRL = 0x2:SW_WKUP.
In addition to programming SW_WKUP(0x2) on CM_GMAC_CLKSTCTRL, SW should also program modulemode field as ENABLED(0x2) on CM_GMAC_GMAC_CLKCTRL register.
If the application does not require Ethernet functionality ever, the developer can choose to place the GMAC module in a power disabled state CM_GMAC_GMAC_CLKCTRL.MODULEMODE = 0x0 (disabled) and CM_GMAC_CLKSTCTRL.CLKTRCTRL = 0x1 (SW_SLEEP) during the boot operation.
SR 1.0
AM574x: 1.0
DRA75xP, DRA74xP, DRA77xP, DRA76xP: 1.0
TDA2Px: 1.0
AM576x: 1.0