From 78f2de9e2390ec4eb4a8304b2051fd897e206eff Mon Sep 17 00:00:00 2001
From: aiminick <aiminick@openfans.org>
Date: Sun, 7 Nov 2021 19:24:34 +0800
Subject: [PATCH] Create pi4_cpu_stepping.md

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 docs/notes/pi4_cpu_stepping.md | 35 ++++++++++++++++++++++++++++++++++
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 create mode 100644 docs/notes/pi4_cpu_stepping.md

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+# BCM2711 SoC Version about stepping
+
+## 2711ZPKFSB06B0T & 2711ZPKFSB06C0T
+
+The new stepping is "**C0T**" than "**B0T**".
+
+Run the command to check:
+
+```
+od -An -tx1 /proc/device-tree/emmc2bus/dma-ranges
+```
+
+It will show different output depending on the stepping:
+
+#### B0
+
+````
+pi@raspberrypi:~$ od -An -tx1 /proc/device-tree/emmc2bus/dma-ranges
+ 00 00 00 00 c0 00 00 00 00 00 00 00 00 00 00 00
+ 40 00 00 00
+````
+
+#### C0
+
+```
+pi@raspberrypi:~$ od -An -tx1 /proc/device-tree/emmc2bus/dma-ranges
+ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
+ fc 00 00 00
+ ```
+ 
+In the case of the BCM2711, it looks like the two main fixes are related to RAM addressing:
+
+- 1.The EMMC2 bus can only directly address the first 1GB.
+- 2.The PCIe interface can only directly address the first 3GB.
+