STM32H7 readme update

Author: jeromecoutant

targets/TARGET_STM/TARGET_STM32H7/README.md

@@ -4,22 +4,20 @@
 
 [GitHub STM32CubeH7 FW](https://github.com/STMicroelectronics/STM32CubeH7)
 
+# Single core STM32
 
-# NUCLEO_H743ZI / NUCLEO_H743ZI2
-
-Note that NUCLEO_H743ZI is deprecated. Please update your board to NUCLEO_H743ZI2:
-- new MCU chip revision
-- new ST Link version
+## STM32H743xx
 
 STM32H743ZI devices are based on the high-performance Arm Cortex-M7 32-bit RISC core operating at up to 480 MHz.
 
 [st.com STM32H743ZI MCU page](https://www.st.com/en/microcontrollers-microprocessors/stm32h743zi.html)
 
+### NUCLEO_H743ZI2
+
 [st.com NUCLEO page](https://www.st.com/en/evaluation-tools/nucleo-h743zi.html)
 
 [mbed.com Target page](https://os.mbed.com/platforms/ST-Nucleo-H743ZI2/)
 
-
 - Total FLASH is 2 MB (0x200000)
     - 2x8 sectors of 128 KB
     - Flash memory bank 1 @ 0x0800 0000
@@ -33,10 +31,53 @@ STM32H743ZI devices are based on the high-performance Arm Cortex-M7 32-bit RISC
     - SRAM3 :      32 KB  (0x8000) @0x3004 0000
     - SRAM4 :      64 KB (0x10000) @0x3800 0000
 
+### NUCLEO_H743ZI
+
+Note that NUCLEO_H743ZI is deprecated. Please update your board to NUCLEO_H743ZI2:
+- new MCU chip revision
+- new ST Link version
+
+**How to use NUCLEO_H743ZI with mbed-os-6:**
+
+PeripheralPins.c and PinNames.h are available in mbed-os repo,
+so you just have to create a custom_targets.json file with:
 
-# DISCO_H747I
+```
+{
+    "NUCLEO_H743ZI": {
+        "inherits": [
+            "MCU_STM32H743xI"
+        ],
+        "config": {
+            "d11_configuration": {
+                "help": "Value: PB_5 for the default board configuration, PA_7 in case of solder bridge update (SB33 on/ SB35 off)",
+                "value": "PB_5",
+                "macro_name": "STM32_D11_SPI_ETHERNET_PIN"
+            },
+            "hse_value": {
+                "value": "8000000",
+                "macro_name": "HSE_VALUE"
+            }
+        },
+        "device_has_add": [
+            "EMAC"
+        ],
+        "overrides": {
+            "network-default-interface-type": "ETHERNET"
+        },
+        "supported_form_factors": [
+            "ARDUINO"
+        ],
+        "device_name": "STM32H743ZI"
+    }
+}
+```
 
-## Overview
+# Dual core STM32
+
+## STM32H747xx
+
+### DISCO_H747I
 
 The STM32H7x7 lines combine the performance of the Cortex-M7 (with double-precision floating point unit) running up to 480 MHz and the Cortex-M4 core (with single-precision floating point unit).
 
@@ -58,6 +99,45 @@ The STM32H7x7 lines combine the performance of the Cortex-M7 (with double-precis
     - SRAM3 :  32 KB  (0x8000) @0x3004 0000 - shared
     - SRAM4 :  64 KB (0x10000) @0x3800 0000 - shared
 
+
+**WARNING**: Ethernet connector is not enabled by default on this board
+
+More information in the wiki page : [Ethernet HW Patch](https://os.mbed.com/teams/ST/wiki/DISCO_H747I-modifications-for-Ethernet)
+
+
+## STM32H745xx
+
+
+[st.com STM32H745 MCU page](https://www.st.com/en/microcontrollers-microprocessors/stm32h745-755.html)
+
+**How to create a custom board with STM32H745xI MCU:**
+
+After creating your local PeripheralPins.c and PinNames.h files in TARGET_BOARD_H745xI directory,
+
+create a custom_targets.json file with:
+
+```
+{
+    "BOARD_H745xI_CM4": {
+        "inherits": [
+            "MCU_STM32H745xI_CM4"
+        ],
+        "extra_labels_add": [
+            "BOARD_H745xI"
+        ]
+    },
+    "BOARD_H745xI_CM7": {
+        "inherits": [
+            "MCU_STM32H745xI_CM7"
+        ],
+        "extra_labels_add": [
+            "BOARD_H745xI"
+        ]
+    }
+}
+```
+
+
 ## Dual mode configuration
 
 Configuration can be checked/changed with STM32CubeProgrammer software in the Option bytes (OB) panel.
@@ -151,10 +231,3 @@ export PATH=$FLASHPATH:$PATH
 STM32_Programmer_CLI -c port=SWD mode=UR -w BUILD/DISCO_H747I_CM4/ARM/mbed-os.bin 0x8100000
 ```
 
-## Ethernet limitation
-
-**WARNING**: Ethernet connector is not enabled by default
-
-More information in the wiki page : [Ethernet HW Patch](https://os.mbed.com/teams/ST/wiki/DISCO_H747I-modifications-for-Ethernet)
-
-