6.1 About the bridge components

Bridge components provide low-power management and external gating on boundaries between clock and power domains along the AXI5 data bus. They also have configurable registering options to ease timing on long AXI5 paths.

The following figure shows the interfaces of a bridge component.

Figure 6-1 Bridge component interfaces
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The following table lists the SIE-300 bridge components.

Table 6-1 Supported bridge components

Bridge component Upstream to downstream clock ratio
Access Control Gate (ACG) One-to-one
Sync-Down Bridge (SDB) N-to-one
Sync-Up Bridge (SUB) One-to-N

Each bridge component consists of an upstream side and a downstream side. To allow communication across clock and power domains, each side of the bridge has one intra-bridge Q-Channel interface and one intra-bridge AXI interface. The eg_on_i signal provides the upstream side with information about the state of external gating on the downstream side. The intra-bridge uses a standard Q-Channel LPI interface.

Each half of a bridge component supports the following features:

Configuration interface

The cfg_gate_resp controls how the upstream side of the bridge component responds, when the bridge is closed by external gating or downstream power quiescence:

  • Responds with an AXI slave error (SLVERR).
  • The bridge component sets the relevant AXI ready signals LOW, which stalls any AXI transactions, until the bridge is able to forward the transfers to the downstream side.

The cfg_ext_gt_err_resp signal controls how the bridge component responds to AXI transactions, when the upstream external gating is in quiescence. However, if the cfg_gate_resp is set to error, then the bridge returns an error response. Therefore, when the upstream external gating is in quiescence, the bridge:

  • Responds with an AXI slave error (SLVERR), when cfg_gate_resp or cfg_ext_gt_err_resp are HIGH.
  • Stalls the transaction until the external gating request is released, that is, ext_gt_qreqn_s goes HIGH. This response behavior requires that cfg_gate_resp and cfg_ext_gt_err_resp are LOW.
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