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-- PowerPC 405 APU FCM "timestamp"

-- record a time (counter value) of User Defined Instruction execution

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-- idea by Pavel Pisa 

-- written by Marek Peca  07/2008

-- KRT FEL CVUT http://dce.felk.cvut.cz/

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The core is a fabric coprocessor module (FCM) for the PowerPC 405 CPU

providing code execution timestamp. It allows to measure precisely CPU

code execution times. A user-defined instruction (UDI) is provided by

the timestamp FCM, which records current time (32bit free running

counter) into the block RAM, which can be read later from the RAM,

mapped into ordinary CPU address space.

User code may execute a new instruction introduced by the FCM, udi0fcm,

with an optional argument (register), bearing so called tag. The current

counter time (ie. in CPU clocks) is stored at that specific instant into

the RAM, together with the tag. The tag can carry any value loadable to

a CPU register, eg. instruction pointer or an arbitrary number. Stored

values can be later dumped by a CPU from the RAM, and delays between

particular time stamps may be thus computed. The instruction execution

lasts 2 CPU cycles.

For more info and block diagram, see frescor_fpga.pdf, Sec. 3.1.

VHDL code of the timestamp FCM has been synthesized by Xilinx ISE 9.2i

and glued by Xilinx EDK 9.2i into Virtex-4 FPGA hardware containing

PowerPC 405 CPU. The FCM has been tested either running without an

operating system (using gcc 4.3.2 and proprietary Xilinx headers), as

well as under Linux 2.6.27-rc4, incorporating Xilinx PowerPC specific

patches and the attached patch (linux-2.6-fcm_udi_enable.diff), enabling

use of UDIs in user space.

File description:

system.mhs.example

        example glue between timestamp and PPC (for EDK)

pcores/timestamp/data/timestamp.mpd

        peripheral description for timestamp core (for EDK)

pcores/timestamp/hdl/vhdl/timestamp.vhdl

        the actual timestamp core (using proprietary Xilinx 16Kb BRAM)

tstamp_linux/linux-2.6-fcm_udi_enable.diff

        Linux kernel patch to enable udi0fcm instruction

tstamp_linux/tstamp_lnx.c

        Linux userspace example code (gcc & Linux glibc)

tstamp_sysless/testapp_tstamp.c

        operating system-less example code (gcc & Xilinx libs)

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Greetings by Marek