decode-dimms出力を復号化する方法

実際のRAMタイミングを知りたいです。スティックのクロックは2400MHzですが、このCPUのメモリクロックは2133MHzに制限されています。以下で確認できます。

$ sudo dmidecode
... 
Handle 0x0004, DMI type 17, 40 bytes
Memory Device
        Array Handle: 0x0003
        Error Information Handle: Not Provided
        Total Width: 64 bits
        Data Width: 64 bits
        Size: 8192 MB
        Form Factor: SODIMM
        Set: None
        Locator: ChannelA-DIMM0
        Bank Locator: BANK 0
        Type: DDR4
        Type Detail: Synchronous Unbuffered (Unregistered)
        Speed: 2133 MT/s
        Manufacturer: Samsung
        Asset Tag: None
        Part Number: M471A1K43BB1-CRC    
        Rank: 1
        Configured Memory Speed: 2133 MT/s
...

現在のメモリタイミングを確認してください。

$ decode-dimms
# decode-dimms version $Revision$

Memory Serial Presence Detect Decoder
By Philip Edelbrock, Christian Zuckschwerdt, Burkart Lingner,
Jean Delvare, Trent Piepho and others


Decoding EEPROM: /sys/bus/i2c/drivers/ee1004/0-0050
Guessing DIMM is in                              bank 1

---=== SPD EEPROM Information ===---
EEPROM CRC of bytes 0-125                        OK (0xFE3E)
# of bytes written to SDRAM EEPROM               384
Total number of bytes in EEPROM                  512
Fundamental Memory type                          DDR4 SDRAM
SPD Revision                                     1.1
Module Type                                      SO-DIMM
EEPROM CRC of bytes 128-253                      OK (0x55EF)

---=== Memory Characteristics ===---
Maximum module speed                             2400 MHz (PC4-19200)
Size                                             8192 MB
Banks x Rows x Columns x Bits                    16 x 16 x 10 x 64
SDRAM Device Width                               8 bits
Ranks                                            1
AA-RCD-RP-RAS (cycles)                           17-17-17-39
Supported CAS Latencies                          18T, 17T, 16T, 15T, 14T, 13T, 12T, 11T, 10T

---=== Timings at Standard Speeds ===---
AA-RCD-RP-RAS (cycles) as DDR4-2400              17-17-17-39
AA-RCD-RP-RAS (cycles) as DDR4-2133              15-15-15-35
AA-RCD-RP-RAS (cycles) as DDR4-1866              13-13-13-30
AA-RCD-RP-RAS (cycles) as DDR4-1600              11-11-11-26

---=== Timing Parameters ===---
Minimum Cycle Time (tCKmin)                      0.833 ns
Maximum Cycle Time (tCKmax)                      1.600 ns
Minimum CAS Latency Time (tAA)                   13.750 ns
Minimum RAS to CAS Delay (tRCD)                  13.750 ns
Minimum Row Precharge Delay (tRP)                13.750 ns
Minimum Active to Precharge Delay (tRAS)         32.000 ns
Minimum Active to Auto-Refresh Delay (tRC)       45.750 ns
Minimum Recovery Delay (tRFC1)                   350.000 ns
Minimum Recovery Delay (tRFC2)                   260.000 ns
Minimum Recovery Delay (tRFC4)                   160.000 ns
Minimum Four Activate Window Delay (tFAW)        21.000 ns
Minimum Row Active to Row Active Delay (tRRD_S)  3.300 ns
Minimum Row Active to Row Active Delay (tRRD_L)  4.900 ns
Minimum CAS to CAS Delay (tCCD_L)                5.000 ns
Minimum Write Recovery Time (tWR)                15.000 ns
Minimum Write to Read Time (tWTR_S)              2.500 ns
Minimum Write to Read Time (tWTR_L)              7.500 ns

どういう意味ですか？時計は2133を指しています。わかりました。さて、今は何時ですか？ 17-17-17-39？ 13-13-13-32？これらのどれも「標準タイミング」に従わないAA-RCD-RP-RAS (cycles) as DDR4-2133 15-15-15-35。なぜそんなことですか？