gem5/src/mem/SimpleDRAM.py

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# Authors: Andreas Hansson
#          Ani Udipi

from m5.params import *
from AbstractMemory import *

# Enum for memory scheduling algorithms, currently First-Come
# First-Served and a First-Row Hit then First-Come First-Served
class MemSched(Enum): vals = ['fcfs', 'frfcfs']

# Enum for the address mapping, currently corresponding to either
# optimising for sequential accesses hitting in the open row, or
# striping across banks.
class AddrMap(Enum): vals = ['openmap', 'closemap']

# Enum for the page policy, either open or close.
class PageManage(Enum): vals = ['open', 'close']

# SimpleDRAM is a single-channel single-ported DRAM controller model
# that aims to model the most important system-level performance
# effects of a DRAM without getting into too much detail of the DRAM
# itself.
class SimpleDRAM(AbstractMemory):
    type = 'SimpleDRAM'
    cxx_header = "mem/simple_dram.hh"

    # single-ported on the system interface side, instantiate with a
    # bus in front of the controller for multiple ports
    port = SlavePort("Slave port")

    # the basic configuration of the controller architecture
    write_buffer_size = Param.Unsigned(32, "Number of read queue entries")
    read_buffer_size = Param.Unsigned(32, "Number of write queue entries")

    # threshold in percent for when to trigger writes and start
    # emptying the write buffer as it starts to get full
    write_thresh_perc = Param.Percent(70, "Threshold to trigger writes")

    # scheduler, address map and page policy
    mem_sched_policy = Param.MemSched('frfcfs', "Memory scheduling policy")
    addr_mapping = Param.AddrMap('openmap', "Address mapping policy")
    page_policy = Param.PageManage('open', "Page closure management policy")

    # the physical organisation of the DRAM
    lines_per_rowbuffer = Param.Unsigned("Row buffer size in cache lines")
    ranks_per_channel = Param.Unsigned("Number of ranks per channel")
    banks_per_rank = Param.Unsigned("Number of banks per rank")

    # timing behaviour and constraints - all in nanoseconds

    # the amount of time in nanoseconds from issuing an activate command
    # to the data being available in the row buffer for a read/write
    tRCD = Param.Latency("RAS to CAS delay")

    # the time from issuing a read/write command to seeing the actual data
    tCL = Param.Latency("CAS latency")

    # minimum time between a precharge and subsequent activate
    tRP = Param.Latency("Row precharge time")

    # time to complete a burst transfer, typically the burst length
    # divided by two due to the DDR bus, but by making it a parameter
    # it is easier to also evaluate SDR memories like WideIO.
    # This parameter has to account for bus width and burst length.
    # Adjustment also necessary if cache line size is greater than
    # data size read/written by one full burst.
    tBURST = Param.Latency("Burst duration (for DDR burst length / 2 cycles)")

    # time taken to complete one refresh cycle (N rows in all banks)
    tRFC = Param.Latency("Refresh cycle time")

    # refresh command interval, how often a "ref" command needs
    # to be sent. It is 7.8 us for a 64ms refresh requirement
    tREFI = Param.Latency("Refresh command interval")

    # write-to-read turn around penalty, assumed same as read-to-write
    tWTR = Param.Latency("Write to read switching time")

    # time window in which a maximum number of activates are allowed
    # to take place, set to 0 to disable
    tXAW = Param.Latency("X activation window")
    activation_limit = Param.Unsigned("Max number of activates in window")

    # Currently rolled into other params
    ######################################################################

    # the minimum amount of time between a row being activated, and
    # precharged (de-activated)
    # tRAS - assumed to be 3 * tRP

    # tRC  - assumed to be 4 * tRP

    # burst length for an access derived from peerBlockSize

# High-level model of a single DDR3 x64 interface (one command and
# address bus), with default timings based on a DDR3-1600 4 Gbit part,
# which would amount to 4 Gbyte of memory in 8x8 or 8 GByte in 16x4
# configuration.
class SimpleDDR3(SimpleDRAM):
    # Assuming 64 byte cache lines, use a 2kbyte page size, this
    # depends on the memory density
    lines_per_rowbuffer = 32

    # Use two ranks
    ranks_per_channel = 2

    # DDR3 has 8 banks in all configurations
    banks_per_rank = 8

    # DDR3-1600 11-11-11
    tRCD = '13.75ns'
    tCL = '13.75ns'
    tRP = '13.75ns'

    # Assuming 64 byte cache lines, across an x64 (8x8 or 16x4)
    # interface, translates to BL8, 4 clocks @ 800 MHz
    tBURST = '5ns'

    # DDR3, 4 Gb has a tRFC of 240 CK and tCK = 1.25 ns
    tRFC = '300ns'

    # DDR3, <=85C, half for >85C
    tREFI = '7.8us'

    # Greater of 4 CK or 7.5 ns, 4 CK @ 800 MHz = 5 ns
    tWTR = '7.5ns'

    # With a 2kbyte page size, DDR3-1600 lands around 40 ns
    tXAW = '40ns'
    activation_limit = 4


# High-level model of a single LPDDR2-S4 x64 interface (one
# command/address bus), with default timings based on a LPDDR2-1066
# 4Gbit part, which whould amount to 1 GByte of memory in 2x32 or
# 2GByte in 4x16 configuration.
class SimpleLPDDR2_S4(SimpleDRAM):
    # Assuming 64 byte cache lines, use a 2kbyte page size, this
    # depends on the memory density
    lines_per_rowbuffer = 32

    # Use two ranks
    ranks_per_channel = 2

    # LPDDR2-S4 has 8 banks in all configurations
    banks_per_rank = 8

    # Fixed at 15 ns
    tRCD = '15ns'

    # 8 CK read latency, 4 CK write latency @ 533 MHz, 1.876 ns cycle time
    tCL = '15ns'

    # Pre-charge one bank 15 ns and all banks 18 ns
    tRP = '18ns'

    # Assuming 64 byte cache lines, across a x64 interface (2x32 or
    # 4x16), translates to BL8, 4 clocks @ 533 MHz
    tBURST = '7.5ns'

    # LPDDR2-S4, 4 Gb
    tRFC = '130ns'
    tREFI = '3.9us'

    # Irrespective of speed grade, tWTR is 7.5 ns
    tWTR = '7.5ns'

    # Irrespective of size, tFAW is 50 ns
    tXAW = '50ns'
    activation_limit = 4