From: Brian Cain <bc...@quicinc.com> Signed-off-by: Brian Cain <brian.c...@oss.qualcomm.com> --- MAINTAINERS | 2 + docs/devel/hexagon-sys.rst | 106 +++++++++++++++++++++++++++++++++ docs/devel/index-internals.rst | 1 + docs/system/hexagon/cdsp.rst | 10 ++++ docs/system/target-hexagon.rst | 100 +++++++++++++++++++++++++++++++ docs/system/targets.rst | 1 + 6 files changed, 220 insertions(+) create mode 100644 docs/devel/hexagon-sys.rst create mode 100644 docs/system/hexagon/cdsp.rst create mode 100644 docs/system/target-hexagon.rst
diff --git a/MAINTAINERS b/MAINTAINERS index 1911949526..804c07bcd5 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -240,6 +240,8 @@ F: disas/hexagon.c F: configs/targets/hexagon-linux-user/default.mak F: docker/dockerfiles/debian-hexagon-cross.docker F: gdb-xml/hexagon*.xml +F: docs/system/target-hexagon.rst +F: docs/devel/hexagon-sys.rst T: git https://github.com/quic/qemu.git hex-next Hexagon idef-parser diff --git a/docs/devel/hexagon-sys.rst b/docs/devel/hexagon-sys.rst new file mode 100644 index 0000000000..3972261a2b --- /dev/null +++ b/docs/devel/hexagon-sys.rst @@ -0,0 +1,106 @@ +.. _Hexagon-System-arch: + +Hexagon System Architecture +=========================== + +The hexagon architecture has some unique elements which are described here. + +Interrupts +---------- +When interrupts arrive at a Hexagon DSP core, they are priority-steered to +be handled by an eligible hardware thread with the lowest priority. + +Memory +------ +Each hardware thread has an ``SSR.ASID`` field that contains its Address +Space Identifier. This value is catenated with a 32-bit virtual address - +the MMU can then resolve this extended virtual address to a physical address. + +TLBs +---- +The format of a TLB entry is shown below. + +.. note:: + The Small Core DSPs have a different TLB format which is not yet + supported. + +.. admonition:: Diagram + + .. code:: text + + 6 5 4 3 + 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |v|g|x|A|A| | | + |a|l|P|1|0| ASID | Virtual Page | + |l|b| | | | | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + 3 2 1 0 + 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | | | | | | | + |x|w|r|u|Cacheab| Physical Page |S| + | | | | | | | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + +* ASID: the address-space identifier +* A1, A0: the behavior of these cache line attributes are not modeled by QEMU. +* xP: the extra-physical bit is the most significant physical address bit. +* S: the S bit and the LSBs of the physical page indicate the page size +* val: this is the 'valid' bit, when set it indicates that page matching + should consider this entry. + +.. list-table:: Page sizes + :widths: 25 25 50 + :header-rows: 1 + + * - S-bit + - Phys page LSBs + - Page size + * - 1 + - N/A + - 4kb + * - 0 + - 0b1 + - 16kb + * - 0 + - 0b10 + - 64kb + * - 0 + - 0b100 + - 256kb + * - 0 + - 0b1000 + - 1MB + * - 0 + - 0b10000 + - 4MB + * - 0 + - 0b100000 + - 16MB + +* glb: if the global bit is set, the ASID is not considered when matching + TLBs. +* Cacheab: the cacheability attributes of TLBs are not modeled, these bits + are ignored. +* RWX: read-, write-, execute-, enable bits. Indicates if user programs + are permitted to read/write/execute the given page. +* U: indicates if user programs can access this page. + +Scheduler +--------- +The Hexagon system architecture has a feature to assist the guest OS +task scheduler. The guest OS can enable this feature by setting +``SCHEDCFG.EN``. The ``BESTWAIT`` register is programmed by the guest OS +to indicate the priority of the highest priority task waiting to run on a +hardware thread. The reschedule interrupt is triggered when any hardware +thread's priority in ``STID.PRIO`` is worse than the ``BESTWAIT``. When +it is triggered, the ``BESTWAIT.PRIO`` value is reset to 0x1ff. + +HVX Coprocessor +--------------- +The Supervisor Status Register field ``SSR.XA`` binds a DSP hardware thread +to one of the eight possible HVX contexts. The guest OS is responsible for +managing this resource. diff --git a/docs/devel/index-internals.rst b/docs/devel/index-internals.rst index bca597c658..27259a552c 100644 --- a/docs/devel/index-internals.rst +++ b/docs/devel/index-internals.rst @@ -14,6 +14,7 @@ Details about QEMU's various subsystems including how to add features to them. block-coroutine-wrapper clocks ebpf_rss + hexagon-sys migration/index multi-process reset diff --git a/docs/system/hexagon/cdsp.rst b/docs/system/hexagon/cdsp.rst new file mode 100644 index 0000000000..f755fbe0a5 --- /dev/null +++ b/docs/system/hexagon/cdsp.rst @@ -0,0 +1,10 @@ +Compute DSP +=========== + +A Hexagon CDSP is designed as a computation offload device for an SoC. The +``V66G_1024`` machine contains: + +* L2VIC interrupt controller +* QTimer timer device + +This machine will support any Hexagon CPU, but will default to ``v66``. diff --git a/docs/system/target-hexagon.rst b/docs/system/target-hexagon.rst new file mode 100644 index 0000000000..e12a93d15d --- /dev/null +++ b/docs/system/target-hexagon.rst @@ -0,0 +1,100 @@ +.. _Hexagon-System-emulator: + +Hexagon System emulator +----------------------- + +Use the ``qemu-system-hexagon`` executable to simulate a 32-bit Hexagon +machine. + +Hexagon Machines +================ + +Hexagon DSPs are suited to various functions and generally appear in a +"DSP subsystem" of a larger system-on-chip (SoC). + +Hexagon DSPs are often included in a subsystem that looks like the diagram +below. Instructions are loaded into DDR before the DSP is brought out of +reset and the first instructions are fetched from DDR via the EVB/reset vector. + +In a real system, a TBU/SMMU would normally arbitrate AXI accesses but +we don't have a need to model that for QEMU. + +Hexagon DSP cores use simultaneous multithreading (SMT) with as many as 8 +hardware threads. + +.. admonition:: Diagram + + .. code:: text + + AHB (local) bus AXI (global) bus + │ │ + │ │ + ┌─────────┐ │ ┌─────────────────┐ │ + │ L2VIC ├──┤ │ │ │ + │ ├──┼───────► ├───────┤ + └─────▲───┘ │ │ Hexagon DSP │ │ + │ │ │ │ │ ┌─────┐ + │ │ │ N threads │ │ │ DDR │ + │ ├───────┤ │ │ │ │ + ┌────┴──┐ │ │ │ ├────────┤ │ + │QTimer ├───┤ │ │ │ │ │ + │ │ │ │ │ │ │ │ + └───────┘ │ │ ┌─────────┐ │ │ │ │ + │ │ ┌─────────┐│ │ │ │ │ + ┌───────┐ │ │ │ HVX xM ││ │ │ │ │ + │QDSP6SS├───┤ │ │ │┘ │ │ │ │ + └───────┘ │ │ └─────────┘ │ │ └─────┘ + │ │ │ │ + ┌───────┐ │ └─────────────────┘ │ + │ CSR ├───┤ + └───────┘ │ ┌──────┐ ┌───────────┐ + │ │ TCM │ │ VTCM │ + │ │ │ │ + └──────┘ │ │ + │ │ + │ │ + │ │ + └───────────┘ + +Components +---------- +Other than l2vic and HVX, the components below are not implemented in QEMU. + +* L2VIC: the L2 vectored interrupt controller. Supports 1024 input + interrupts, edge- or level-triggered. The core ISA has system registers + ``VID``, ``VID1`` which read through to the L2VIC device. +* QTimer: ARMSSE-based programmable timer device. Its interrupts are + wired to the L2VIC. System registers ``TIMER``, ``UTIMER`` read + through to the QTimer device. +* QDSP6SS: DSP subsystem features, accessible to the entire SoC, including + DSP NMI, watchdog, reset, etc. +* CSR: Configuration/Status Registers. +* TCM: DSP-exclusive tightly-coupled memory. This memory can be used for + DSPs when isolated from DDR and in some bootstrapping modes. +* VTCM: DSP-exclusive vector tightly-coupled memory. This memory is accessed + by some HVX instructions. +* HVX: the vector coprocessor supports 64 and 128-byte vector registers. + 64-byte mode is not implemented in QEMU. + + +Bootstrapping +------------- +Hexagon systems do not generally have access to a block device. So, for +QEMU the typical use case involves loading a binary or ELF file into memory +and executing from the indicated start address:: + + $ qemu-system-hexagon -kernel ./prog -append 'arg1 arg2' + +Semihosting +----------- +Hexagon supports a semihosting interface similar to other architectures'. +The ``trap0`` instruction can activate these semihosting calls so that the +guest software can access the host console and filesystem. Semihosting +is not yet implemented in QEMU hexagon. + + +Hexagon Features +================ +.. toctree:: + hexagon/cdsp + diff --git a/docs/system/targets.rst b/docs/system/targets.rst index 224fadae71..e6dcdb9d41 100644 --- a/docs/system/targets.rst +++ b/docs/system/targets.rst @@ -29,3 +29,4 @@ Contents: target-sparc64 target-i386 target-xtensa + target-hexagon -- 2.34.1
