Limiting over sampling to improve transmission schedulability in a mixed NoC/AFDX architecture

Abstract

Current avionics architecture are based on an avionics full duplex switched Ethernet network (AFDX) that interconnects end systems. Avionics functions exchange data through Virtual Links (VLs), which are static flows with bounded bandwidth. The jitter for each VL at AFDX entrance has to be less than 500μs. This constraint is met, thanks to end system scheduling. The interconnection of many-cores by an AFDX backbone is envisioned for future avionics architecture. The principle is to distribute avionics functions on these many-cores. Many-cores are based on simple cores interconnected by a Network-on-Chip (NoC). The allocation of functions on the available cores as well as the transmission of flows on the NoC has to be performed in such a way that the jitter for each VL at AFDX entrance is still less than 500μs. A first solution has been proposed, where a single task in each many-core manages the transmission of the VLs. This task executes a scheduling table. The access to the Ethernet interface is then only allowed to one VL leading to a significant reduction of the jitter. By oversampling the VL transmissions in a minimum period, the waiting delays are also reduced. But this solution limits the number of VLs. In this paper, we propose to improve the transmission scheduling by relaxing constraint on the over sampling. A new scheduling table is constructed using an Integer Linear Program. This solution increases the number of VLs transmitted by the many-core and still reduces the waiting delays for the transmission of the VLs.