mem: Replacing bytesPerCacheLine with DRAM burstLength in SimpleDRAM

This patch gets rid of bytesPerCacheLine parameter and makes the DRAM
configuration separate from cache line size. Instead of
bytesPerCacheLine, we define a parameter for the DRAM called
burst_length. The burst_length parameter shows the length of a DRAM
device burst in bits. Also, lines_per_rowbuffer is replaced with
device_rowbuffer_size to improve code portablity.

This patch adds a burst length in beats for each memory type, an
interface width for each memory type, and the memory controller model
is extended to reason about "system" packets vs "dram" packets and
assemble the responses properly. It means that system packets larger
than a full burst are split into multiple dram packets.

1 files changed, 73 insertions, 28 deletions

diff --git a/src/mem/SimpleDRAM.py b/src/mem/SimpleDRAM.py
index ec76542d8..b066b27de 100644
--- a/src/mem/SimpleDRAM.py
+++ b/src/mem/SimpleDRAM.py
@@ -10,6 +10,9 @@
 # unmodified and in its entirety in all distributions of the software,
 # modified or unmodified, in source code or in binary form.
 #
+# Copyright (c) 2013 Amin Farmahini-Farahani
+# All rights reserved.
+#
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met: redistributions of source code must retain the above copyright
@@ -118,7 +121,12 @@ class SimpleDRAM(AbstractMemory):
     static_backend_latency = Param.Latency("10ns", "Static backend latency")
 
     # the physical organisation of the DRAM
-    lines_per_rowbuffer = Param.Unsigned("Row buffer size in cache lines")
+    device_bus_width = Param.Unsigned("data bus width in bits for each DRAM "\
+                                      "device/chip")
+    burst_length = Param.Unsigned("Burst lenght (BL) in beats")
+    device_rowbuffer_size = Param.MemorySize("Page (row buffer) size per "\
+                                           "device/chip")
+    devices_per_rank = Param.Unsigned("Number of devices/chips per rank")
     ranks_per_channel = Param.Unsigned("Number of ranks per channel")
     banks_per_rank = Param.Unsigned("Number of banks per rank")
     # only used for the address mapping as the controller by
@@ -141,9 +149,9 @@ class SimpleDRAM(AbstractMemory):
     # 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.
+    # This parameter has to account for burst length.
+    # Read/Write requests with data size larger than one full burst are broken
+    # down into multiple requests in the SimpleDRAM controller
     tBURST = Param.Latency("Burst duration (for DDR burst length / 2 cycles)")
 
     # time taken to complete one refresh cycle (N rows in all banks)
@@ -170,15 +178,22 @@ class SimpleDRAM(AbstractMemory):
 
     # tRC  - assumed to be 4 * tRP
 
-    # burst length for an access derived from the cache line size
-
 # A single DDR3 x64 interface (one command and address bus), with
 # default timings based on DDR3-1600 4 Gbit parts in an 8x8
 # configuration, which would amount to 4 Gbyte of memory.
 class DDR3_1600_x64(SimpleDRAM):
-    # Assuming 64 byte cache lines, and a 1kbyte page size per module
+    # 8x8 configuration, 8 devices each with an 8-bit interface
+    device_bus_width = 8
+
+    # DDR3 is a BL8 device
+    burst_length = 8
+
+    # Each device has a page (row buffer) size of 1KB
     # (this depends on the memory density)
-    lines_per_rowbuffer = 128
+    device_rowbuffer_size = '1kB'
+
+    # 8x8 configuration, so 8 devices
+    devices_per_rank = 8
 
     # Use two ranks
     ranks_per_channel = 2
@@ -191,8 +206,8 @@ class DDR3_1600_x64(SimpleDRAM):
     tCL = '13.75ns'
     tRP = '13.75ns'
 
-    # Assuming 64 byte cache lines, across an x64
-    # interface, translates to BL8, 4 clocks @ 800 MHz
+    # 8 beats across an x64 interface translates to 4 clocks @ 800 MHz.
+    # Note this is a BL8 DDR device.
     tBURST = '5ns'
 
     # DDR3, 4 Gbit has a tRFC of 240 CK and tCK = 1.25 ns
@@ -213,9 +228,18 @@ class DDR3_1600_x64(SimpleDRAM):
 # default timings based on a LPDDR2-1066 4 Gbit part in a 1x32
 # configuration.
 class LPDDR2_S4_1066_x32(SimpleDRAM):
-    # Assuming 64 byte cache lines, use a 1kbyte page size, this
-    # depends on the memory density
-    lines_per_rowbuffer = 16
+    # 1x32 configuration, 1 device with a 32-bit interface
+    device_bus_width = 32
+
+    # LPDDR2_S4 is a BL4 and BL8 device
+    burst_length = 8
+
+    # Each device has a page (row buffer) size of 1KB
+    # (this depends on the memory density)
+    device_rowbuffer_size = '1kB'
+
+    # 1x32 configuration, so 1 device
+    devices_per_rank = 1
 
     # Use a single rank
     ranks_per_channel = 1
@@ -232,10 +256,11 @@ class LPDDR2_S4_1066_x32(SimpleDRAM):
     # Pre-charge one bank 15 ns (all banks 18 ns)
     tRP = '15ns'
 
-    # Assuming 64 byte cache lines, across a x32 DDR interface
-    # translates to two BL8, 8 clocks @ 533 MHz. Note that this is a
-    # simplification
-    tBURST = '15ns'
+    # 8 beats across an x32 DDR interface translates to 4 clocks @ 533 MHz.
+    # Note this is a BL8 DDR device.
+    # Requests larger than 32 bytes are broken down into multiple requests
+    # in the SimpleDRAM controller
+    tBURST = '7.5ns'
 
     # LPDDR2-S4, 4 Gbit
     tRFC = '130ns'
@@ -251,9 +276,18 @@ class LPDDR2_S4_1066_x32(SimpleDRAM):
 # A single WideIO x128 interface (one command and address bus), with
 # default timings based on an estimated WIO-200 8 Gbit part.
 class WideIO_200_x128(SimpleDRAM):
-    # Assuming 64 byte cache lines, use a 4kbyte page size, this
-    # depends on the memory density
-    lines_per_rowbuffer = 64
+    # 1x128 configuration, 1 device with a 128-bit interface
+    device_bus_width = 128
+
+    # This is a BL4 device
+    burst_length = 4
+
+    # Each device has a page (row buffer) size of 4KB
+    # (this depends on the memory density)
+    device_rowbuffer_size = '4kB'
+
+    # 1x128 configuration, so 1 device
+    devices_per_rank = 1
 
     # Use one rank for a one-high die stack
     ranks_per_channel = 1
@@ -266,8 +300,8 @@ class WideIO_200_x128(SimpleDRAM):
     tCL = '18ns'
     tRP = '18ns'
 
-    # Assuming 64 byte cache lines, across an x128 SDR interface,
-    # translates to BL4, 4 clocks @ 200 MHz
+    # 4 beats across an x128 SDR interface translates to 4 clocks @ 200 MHz.
+    # Note this is a BL4 SDR device.
     tBURST = '20ns'
 
     # WIO 8 Gb
@@ -287,9 +321,18 @@ class WideIO_200_x128(SimpleDRAM):
 # default timings based on a LPDDR3-1600 4 Gbit part in a 1x32
 # configuration
 class LPDDR3_1600_x32(SimpleDRAM):
-    # 4 Gbit and 8 Gbit devices use a 1 kByte page size, so ssuming 64
-    # byte cache lines, that is 16 lines
-    lines_per_rowbuffer = 16
+    # 1x32 configuration, 1 device with a 32-bit interface
+    device_bus_width = 32
+
+    # LPDDR3 is a BL8 device
+    burst_length = 8
+
+    # Each device has a page (row buffer) size of 1KB
+    # (this depends on the memory density)
+    device_rowbuffer_size = '1kB'
+
+    # 1x32 configuration, so 1 device
+    devices_per_rank = 1
 
     # Use a single rank
     ranks_per_channel = 1
@@ -306,9 +349,11 @@ class LPDDR3_1600_x32(SimpleDRAM):
     # Pre-charge one bank 15 ns (all banks 18 ns)
     tRP = '15ns'
 
-    # Assuming 64 byte cache lines, across a x32 DDR interface
-    # translates to two bursts of BL8, 8 clocks @ 800 MHz
-    tBURST = '10ns'
+    # 8 beats across a x32 DDR interface translates to 4 clocks @ 800 MHz.
+    # Note this is a BL8 DDR device.
+    # Requests larger than 32 bytes are broken down into multiple requests
+    # in the SimpleDRAM controller
+    tBURST = '5ns'
 
     # LPDDR3, 4 Gb
     tRFC = '130ns'