Hexagon
Hexagon (QDSP6) is a DSP based 32-bit multithreaded CPU architecture developed by Qualcomm. According to 2012 estimation, Qualcomm shipped 1.2 billion DSP cores inside its SoCs (average 2.3 DSP core per SoC) in 2011 year, and 1.5 billion cores were planned for 2012, making the QDSP most shipped architecture of DSP (CEVA had around 1 billion of DSP cores shipped in 2011 with 90% of IP-licenseable DSP market). The Hexagon architecture is designed to deliver performance with low power over a variety of applications. It has features such as hardware assisted multithreading, privilege levels, VLIW, SIMD, and instructions geared toward efficient signal processing. The CPU is capable of in-order dispatching up to 4 instructions (the packet) to 4 Execution Units every clock. Hardware multithreading is implemented as barrel temporal multithreading – threads are switched in round-robin fashion each cycle, so 600 MHz physical core is presented as three logical 200 MHz cores before V5. Hexagon V5 switched to dynamic multithreading (DMT) with thread switch on L2 misses, interrupt waiting or on special instructions. The port of Linux for Hexagon runs under a hypervisor layer (“Hexagon Virtual Machine”) and was merged with the 3.2 release of the kernel. The original hypervisor is closed-source, and in April 2013 a minimal open-source hypervisor implementation for QDSP6 V2 and V3, the “Hexagon MiniVM” was released by Qualcomm under a BSD-style license. Support for Hexagon was added in 3.1 release of LLVM by Tony Linthicum. There is also a non-FSF maintained branch of GCC and binutils. Hexagon DSPs are included in Snapdragon SoC since 2006. In Snapdragon S4 (MSM8960 and newer) there are three QDSP cores, two in the Modem subsystem and one Hexagon core in the Multimedia subsystem. Modem cores are programmed by Qualcomm only, and only Multimedia core is allowed to be programmed by user. They are also used in some femtocell processors of Qualcomm, including FSM9832.
