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FatFs library for Raspberry Pi Pico

Scene

Overview

FatFs library on Raspberry Pi Pico. This library supports:

Supported Board

  • Raspberry Pi Pico and Raspberry Pi Pico W

Ciruit Diagram

Circuit Diagram

Pin Assignment

microSD card

Pico Pin # Pin Name Function microSD connector microSD SPI board
4 GP2 SPI0_SCK CLK (5) CLK
5 GP3 SPI0_TX CMD (3) MOSI
6 GP4 SPI0_RX DAT0 (7) MISO
7 GP5 SPI0_CSn CD/DAT3 (2) CS
8 GND GND VSS (6) GND
36 3V3(OUT) 3.3V VDD (4) 3V3

Caution

  • Wire length between Pico and SD card is very sensitive. Short wiring as possible is desired, otherwise errors such as Mount error, Preallocation error and Write fail will occur.

Serial (CP2102 module)

Pico Pin # Pin Name Function CP2102 module
1 GP0 UART0_TX RXD
2 GP1 UART0_RX TXD
3 GND GND GND

How to build

  • See "Getting started with Raspberry Pi Pico"
  • Put "pico-sdk", "pico-examples" and "pico-extras" on the same level with this project folder.
  • Set environmental variables for PICO_SDK_PATH, PICO_EXTRAS_PATH and PICO_EXAMPLES_PATH
  • Confirmed with Pico SDK 2.0.0
> git clone -b 2.0.0 https://github.com/raspberrypi/pico-sdk.git
> cd pico-sdk
> git submodule update -i
> cd ..
> git clone -b sdk-2.0.0 https://github.com/raspberrypi/pico-examples.git
>
> git clone -b sdk-2.0.0 https://github.com/raspberrypi/pico-extras.git
> 
> git clone -b main https://github.com/elehobica/pico_fatfs.git

Windows

  • Build is confirmed with Developer Command Prompt for VS 2022 and Visual Studio Code on Windows environment
  • Confirmed with cmake-3.27.2-windows-x86_64 and gcc-arm-none-eabi-10.3-2021.10-win32
  • Lanuch "Developer Command Prompt for VS 2022"
> cd pico_fatfs/test
> mkdir build && cd build
> cmake -G "NMake Makefiles" ..
> nmake
  • Put "pico_fatfs_test.uf2" on RPI-RP2 drive

Linux

$ cd pico_fatfs/test
$ mkdir build && cd build
$ cmake ..
$ make -j4
  • Download "pico_fatfs_test.uf2" on RPI-RP2 drive

Configuration

Configure clock and pin settings by pico_fatfs_set_config() with pico_fatfs_spi_config_t

  pico_fatfs_spi_config_t config = {
      spi0,                   // spi_inst
      CLK_SLOW_DEFAULT,       // clk_slow
      CLK_FAST_DEFAULT,       // clk_fast
      PIN_SPI0_MISO_DEFAULT,  // pin_miso
      PIN_SPI0_CS_DEFAULT,    // pin_cs
      PIN_SPI0_SCK_DEFAULT,   // pin_sck
      PIN_SPI0_MOSI_DEFAULT,  // pin_mosi
      true                    // pullup
  };
  pico_fatfs_set_config(&config);

Clock confguration

  • By default, clk_slow is set to 100 * KHZ and clk_fast is set to 50 * MHZ.
  • The actual SPI clock frequency is set to clk_peri / N = 125.0 MHz / N, which is determined by spi_set_baudrate() in 'pico-sdk/src/rp2_common/hardware_spi/spi.c'.
  • Thus, to choose actually slower clock as clk_fast, smaller value than 31.25 MHz should be configured.

Pin assignment

  • Choose spi0 or spi1 and designate corresponding pin assignment for pin_miso, pin_cs, pin_sck and pin_mosi.
  • Pin selection must follow pin assignment rule defined by spi0 or spi1. See comments PIN_SPIx_XXX_DEFAULT in tf_card.h.

Pullup option

  • set true for MISO, MOSI to use internal pullup. (recommended)
  • set false for MISO, MOSI when external pullup resistors attached. external pullup

Other customization for pin configuration

By default, void pico_fatfs_init_spi() in tf_card.c runs for IO buffer initialization. User can override it by the re-definition to get more detail IO buffer configuration. However, the customizations such as slew rate and/or drive strength rarely improve the timing problem of SPI interface, therefore, physical approach such as shorter wiring would be recommended.

in C++ code (e.g. main.cpp)

extern "C" {
void pico_fatfs_init_spi(void)
{
  ...
}
}

or in C code (e.g. main.c)

void pico_fatfs_init_spi(void)
{
  ...
}

Function customization

User can also override following functions as they are defined with weak attribute.

Benchmark Result (CLK_FAST = 50 MHz)

  • Memorex microSD 2GB
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is FAT16
Card size:    2.00 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
79.8977, 215736, 2447, 6404
78.9926, 210883, 2460, 6457

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
827.0769, 2173, 500, 618
827.2137, 2171, 500, 618
  • SanDisk microSDHC 16GB (C4)
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is FAT32
Card size:   15.92 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
247.8279, 31470, 1621, 2063
232.7164, 56411, 1596, 2197

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
792.8449, 3412, 621, 644
792.9706, 3411, 633, 644
  • Sansung microSDHC EVO Plus 32GB (UHS-I U1)
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is FAT32
Card size:   32.00 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
447.7192, 6896, 1007, 1142
446.4797, 7589, 1024, 1145

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
974.9766, 1050, 403, 524
974.4066, 1049, 402, 524
  • SanDisk microSDXC Ultra A1 64GB (UHS-I U1)
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is EXFAT
Card size:   63.83 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
457.3436, 39688, 890, 1118
459.7830, 19127, 896, 1112

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
1226.3135, 426, 398, 416
1226.0127, 425, 408, 416
  • SanDisk microSDXC Ultra A1 128GB (UHS-I C10 U1)
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is EXFAT
Card size:  127.83 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
446.6393, 37701, 951, 1145
444.8114, 36075, 960, 1150

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
1310.1887, 416, 381, 389
1310.1887, 414, 381, 389
  • SanDisk microSDXC Ultra A1 512GB (UHS-I U1)
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is EXFAT
Card size:  511.80 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
430.6728, 5316, 952, 1187
430.5244, 25833, 953, 1188

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
1304.3778, 408, 366, 391
1304.7181, 408, 378, 391
  • SanDisk microSDXC Ultra A2 1TB (UHS-I U3 V30)
=====================
== pico_fatfs_test ==
=====================
mount ok
Type is EXFAT
Card size: 1023.74 GB (GB = 1E9 bytes)

FILE_SIZE_MB = 5
BUF_SIZE = 512 bytes
Starting write test, please wait.

write speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
417.6842, 32387, 989, 1224
414.7391, 19074, 986, 1233

Starting read test, please wait.

read speed and latency
speed,max,min,avg
KB/Sec,usec,usec,usec
1288.9095, 412, 368, 396
1289.2418, 412, 381, 396

Application Example