Methods and apparatus for upgrading programmable control logic without disturbing network traffic flowing through functional elements controlled by the control logic

摘要

A network device includes latches disposed between control outputs of control logic such as a field-programmable gate array (FPGA) and control inputs of functional elements through which network traffic flows. The control logic generates a latch enable signal that controls the operation of the latches. The latch enable signal is in a latching state to maintain the latches open during normal operation. During an upgrade, the control outputs may take on incorrect or indeterminate values, due to entering a high-impedance state. Therefore, during the upgrade the latches are closed, maintaining the pre-upgrade values on the inputs of the functional elements and preventing the control logic outputs from affecting operation of the device. After re-programming is complete and the control outputs are in a determinate state, the latches are re-opened. A pullup/pulldown circuit is used to maintain the latch enable signal in a latching state during the upgrade.