open the QSPI for Seeed XIAO BLE and add example code of it

how to compile the libmbed.a for QSPI:
1 git clone https://github.com/Seeed-Studio/ArduinoCore-mbed.git
2 git clone https://github.com/arduino/mbed-os.git
3 cd mbed-os/
4 git apply /path/of/ArduinoCore-mbed/patch/0091-add-support-for-Seeed-XIAO-BLE.patch
5 git apply /path/of/ArduinoCore-mbed/patch/0092-open-the-QSPI-for-Seeed-XIAO-BLE.patch
6 cd ArduinoCore-mbed/
7 ./mbed-os-to-arduino -r /absolute/path/of/mbed-os/ SEEED_XIAO_NRF52840_SENSE:SEEED_XIAO_NRF52840_SENSE

libraries/Spi_Flash/example/flash_write_read/flash_write_read.ino

@@ -0,0 +1,63 @@
+/*
+  Spi Flash write read demo
+  This demo is based on Seeed XIAO BLE.
+  The spi flash chip is P25Q16H(https://www.puyasemi.com/uploadfiles/2018/08/20180807152503253.pdf)
+*/
+
+#include "QSPIFBlockDevice.h"
+
+using namespace mbed;
+
+QSPIFBlockDevice root(QSPI_FLASH1_IO0, QSPI_FLASH1_IO1, QSPI_FLASH1_IO2, QSPI_FLASH1_IO3, QSPI_FLASH1_SCK, QSPI_FLASH1_CSN, QSPIF_POLARITY_MODE_1, MBED_CONF_QSPIF_QSPI_FREQ);
+
+void setup() {
+
+  Serial.begin(115200);
+  while (!Serial);
+
+  Serial.println("init the spi flash...");
+  int ret = root.init();
+  if(ret) {
+    Serial.print("init error. err code=");
+    Serial.println(ret);
+  }
+
+  Serial.print("QSPIF BD size:");
+  Serial.println(root.size());
+  Serial.print("QSPIF read size:");
+  Serial.println(root.get_read_size());
+  Serial.print("QSPIF program size:");
+  Serial.println(root.get_program_size());
+  uint64_t sector_size_at_address_0 = root.get_erase_size(0);
+  Serial.print("QSPIF erase size:");
+  Serial.println(sector_size_at_address_0);
+
+  // Init the buffer for write and read
+  char *write_buffer = (char *) malloc(sector_size_at_address_0);
+  char *read_buffer = (char *) malloc(sector_size_at_address_0);
+  memset(write_buffer, 0x00, sector_size_at_address_0);
+  memset(read_buffer, 0x00, sector_size_at_address_0);
+
+  // Write the data to the spi flash
+  sprintf(write_buffer, "Hello World!\n");
+  Serial.println("writing data to spi flash...");
+  root.erase(0, sector_size_at_address_0);
+  root.program(write_buffer, 0, sector_size_at_address_0);
+
+  // Read back what was stored
+  Serial.println("Reading data from spi flash...");
+  root.read(read_buffer, 0, sector_size_at_address_0);
+  Serial.println(read_buffer);
+
+  if(!memcmp(write_buffer, read_buffer, sector_size_at_address_0)){
+    Serial.println("spi flash read write success");
+  } else {
+    Serial.println("spi flash read write failed");
+  }
+
+  root.deinit();
+}
+
+void loop() {
+
+}

patches/0092-open-the-QSPI-for-Seeed-XIAO-BLE.patch

@@ -0,0 +1,70 @@
+From 61180bcbb9bf8f9b139cff3a1fe625890e49fe2f Mon Sep 17 00:00:00 2001
+From: bbear <953308023@qq.com>
+Date: Wed, 26 Jan 2022 08:50:29 +0000
+Subject: [PATCH] open the QSPI for Seeed XIAO BLE
+
+---
+ storage/blockdevice/COMPONENT_QSPIF/mbed_lib.json |  3 ++-
+ .../TARGET_SEEED_XIAO_NRF52840_SENSE/PinNames.h   | 15 +++++++++++++++
+ targets/targets.json                              |  4 ----
+ 3 files changed, 17 insertions(+), 5 deletions(-)
+
+diff --git a/storage/blockdevice/COMPONENT_QSPIF/mbed_lib.json b/storage/blockdevice/COMPONENT_QSPIF/mbed_lib.json
+index ca461079..24c86d6e 100644
+--- a/storage/blockdevice/COMPONENT_QSPIF/mbed_lib.json
++++ b/storage/blockdevice/COMPONENT_QSPIF/mbed_lib.json
+@@ -37,7 +37,8 @@
+         "MCU_NRF52840": {
+             "QSPI_FREQ": "32000000",
+             "QSPI_MIN_READ_SIZE": "4",
+-            "QSPI_MIN_PROG_SIZE": "4"
++            "QSPI_MIN_PROG_SIZE": "4",
++            "qspif.direct-reset": true
+         }, 
+         "MCU_PSOC6": {
+             "QSPI_FREQ": "50000000"
+diff --git a/targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/TARGET_SEEED_XIAO_NRF52840_SENSE/PinNames.h b/targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/TARGET_SEEED_XIAO_NRF52840_SENSE/PinNames.h
+index e2b1cbad..3fc2080d 100644
+--- a/targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/TARGET_SEEED_XIAO_NRF52840_SENSE/PinNames.h
++++ b/targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/TARGET_SEEED_XIAO_NRF52840_SENSE/PinNames.h
+@@ -179,6 +179,21 @@ typedef enum {
+     I2C_SDA0 = p4,
+     I2C_SCL0 = p5,
+
++    /**** QSPI pins ****/
++    QSPI1_IO0 = P0_20,
++    QSPI1_IO1 = P0_24,
++    QSPI1_IO2 = P0_22,
++    QSPI1_IO3 = P0_23,
++    QSPI1_SCK = P0_21,
++    QSPI1_CSN = P0_25,
++
++    QSPI_FLASH1_IO0 = P0_20,
++    QSPI_FLASH1_IO1 = P0_24,
++    QSPI_FLASH1_IO2 = P0_22,
++    QSPI_FLASH1_IO3 = P0_23,
++    QSPI_FLASH1_SCK = P0_21,
++    QSPI_FLASH1_CSN = P0_25,
++
+ #ifndef ARDUINO_ARCH_MBED
+     // Digital Pins
+     D0  = P0_2,
+diff --git a/targets/targets.json b/targets/targets.json
+index fff0bf72..725509ba 100644
+--- a/targets/targets.json
++++ b/targets/targets.json
+@@ -6447,11 +6447,7 @@
+         "features_add": [
+             "STORAGE"
+         ],
+-        "components_remove": [
+-            "QSPIF"
+-        ],
+         "device_has_remove": [
+-            "QSPI",
+             "ITM"
+         ],
+         "macros_add": [
+-- 
+2.20.1
+