diff options
author | Patrick Rudolph <siro@das-labor.org> | 2017-11-01 16:52:02 +0100 |
---|---|---|
committer | Martin Roth <martinroth@google.com> | 2017-12-09 16:59:16 +0000 |
commit | bf8db8d45b35181c84a163ab669f7a8d39ad5fec (patch) | |
tree | 002cd89138145cdaf7fc164777d240ab3cb4ddf9 /Documentation/Intel/NativeRaminit/Sandybridge_read.md | |
parent | dc27d629219346d0e631a7c54e664ba9301fa011 (diff) | |
download | coreboot-bf8db8d45b35181c84a163ab669f7a8d39ad5fec.tar.xz |
Documentation/Intel: Add NativeRaminit documentation
Add documentation for Intel native raminit on Intel SandyBridge.
Documented so far:
* Register
* Read training
* Frequency selection
* SMBIOS type 17 memory reporting
* Various Kconfig options and features
Change-Id: I3b977460ecb29c9a54e3fab82349982fca9918e7
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/22275
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Diffstat (limited to 'Documentation/Intel/NativeRaminit/Sandybridge_read.md')
-rw-r--r-- | Documentation/Intel/NativeRaminit/Sandybridge_read.md | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/Documentation/Intel/NativeRaminit/Sandybridge_read.md b/Documentation/Intel/NativeRaminit/Sandybridge_read.md new file mode 100644 index 0000000000..d43f9316e4 --- /dev/null +++ b/Documentation/Intel/NativeRaminit/Sandybridge_read.md @@ -0,0 +1,142 @@ +# Read training + +## Introduction + +This chapter explains the read training sequence done on Sandy Bride and +Ivy Bridge memory initialization. + +Read training is done to compensate the skew between DQS and SCK and to find +the smallest supported roundtrip delay. + +Every board does have a vendor depended routing topology, and can be equip +with any combination of DDR3 memory modules, that introduces different +skew between the memory lanes. With DDR3 a "Fly-By" routing topology +has been introduced, that makes the biggest part of DQS-SCK skew. +The memory code measures the actual skew and actives delay gates, +that will "compensate" the skew. + +When in read training the DRAM and the controller are placed in a special mode. +On every read instruction the DRAM outputs a predefined pattern and the memory +controller samples the DQS after a given delay. As the pattern is known, the +actual delay of every lane can be measured. + +The values programmed in read training effect DRAM-to-MC transfers only ! + +## Definitions +| Symbol | Description | Units | Valid region | +|---------|-------------------------------------------------------------------|------------|--------------| +| SCK | DRAM system clock cycle time | s | - | +| tCK | DRAM system clock cycle time | 1/256th ns | - | +| DCK | Data clock cycle time: The time between two SCK clock edges | s | - | +| timA | IO phase: The phase delay of the IO signals | 1/64th DCK | [0-512) | +| SPD | Manufacturer set memory timings located on an EEPROM on every DIMM| bytes | - | +| REFCK | Reference clock, either 100 or 133 | Mhz | 100, 133 | +| MULT | DRAM PLL multiplier | - | [3-12] | +| XMP | Extreme Memory Profiles | - | - | +| DQS | Data Strobe signal used to sample all lane's DQ signals | - | - | + +## Hardware +The hardware does have delay logic blocks that can delay the DQ / DQS of a +lane/rank by one or multiple clock cylces and it does have delay logic blocks +that can delay the signal by a multiple of 1/64th DCK per lane. + +All delay values can be controlled via software by writing registers in the +MCHBAR. + +## IO phase + +The IO phase can be adjusted in [0-512) * 1/64th DCK. Incrementing it by 64 is +the same as Incrementing IO delay by 1. + +## IO delay +Delays the DQ / DQS signal by one or multiple clock cycles. + +### Roundtrip time +The roundtrip time is the time the memory controller waits for data arraving +after a read has been issued. Due to clock-domain crossings, multiple +delay instances and phase interpolators, the signal runtime to DRAM and back +to memory controller defaults to 55 DCKs. The real roundtrip time has to be +measured. + +After a read command has been issued, a counter counts down until zero has been +reached and activates the input buffers. + +The following pictures shows the relationship between those three values. +The picture was generated from 16 IO delay values times 64 timA values. +The highest IO delay was set on the right-hand side, while the last block +on the left-hand side has zero IO delay. + +** roundtrip 55 DCKs ** +![alt text][timA_lane0-3_rt55] + +[timA_lane0-3_rt55]: timA_lane0-3_rt55.png "timA for lane0 - lane3, roundtrip 55" + +** roundtrip 54 DCKs ** +![alt text][timA_lane0-3_rt54] + +[timA_lane0-3_rt54]: timA_lane0-3_rt54.png "timA for lane0 - lane3, roundtrip 54" + + +** roundtrip 53 DCKs ** +![alt text][timA_lane0-3_rt53] + +[timA_lane0-3_rt53]: timA_lane0-3_rt53.png "timA for lane0 - lane3, roundtrip 53" + +As you can see the signal has some jitter as every sample was taken in a +different loop iteration. The result register only contains a single bit per +lane. + +## Algorithm +### Steps +The algorithm finds the roundtrip time, IO delay and IO phase. The IO phase +will be adjusted to match the falling edge of the preamble of each lane. +The roundtrip time is adjusted to an minimal value, that still includes the +preamble. + +### Synchronize to data phase + +The first measurement done in read-leveling samples all DQS values for one +phase [0-64) * 1/64th DCK. It then searches for the middle of the low data +symbol and adjusts timA to the found phase and thus the following measurements +will be aligned to the low data symbol. +The code assumes that the initial roundtrip time causes the measurement to be +in the alternating pattern data phase. + +### Finding the preamble +After adjusting the IO phase to the middle of one data symbol the preamble will +be located. Unlike the data phase, which is an alternating pattern (010101...), +the preamble consists of two high data cycles. + +The code decrements the IO delay/RTT and samples the DQS signal with timA +untouched. As it has been positioned in the middle of the data symbol, it'll +read as either "low" or "high". + +If it's "low" we are still in the data phase. +If it's "high" we have found the preamble. + +The roundtrip time and IO delay will be adjusted until all lanes are aligned. +The resulting IO delay is visible in the picture below. + +** roundtrip time: 49 DCKs, IO delay (at blue point): 6 DCKs ** +![alt text][timA_lane0-3_discover_420x] + +[timA_lane0-3_discover_420x]: timA_lane0-3_discover_420x.png "timA for lane0 - lane3, finding minimum roundtrip time" + +** Note: The sampled data has been shifted by timA. The preamble is now +in phase. ** + +## Fine adjustment + +As timA still points the middle of the data symbol an offset of 32 is added. +It now points the falling edge of the preamble. +The fine adjustment is to reduce errors introduced by jitter. The phase is +adjusted from `timA - 25` to `timA + 25` and the DQS signal is sampled 100 +times. The fine adjustment finds the middle of each rising edge (it's actual +the falling edge of the preamble) to get the final IO phase. You can see the +result in the picture below. + +![alt text][timA_lane0-3_adjust_fine] + +[timA_lane0-3_adjust_fine]: timA_lane0-3_adjust_fine.png "timA for lane0 - lane3, fine adjustment" + +Lanes 0 - 2 will be adjusted by a phase of -10, while lane 3 is already correct. |