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CH554 software development kit for SDCC Linux build


This is a port of the CH554 SDK, from Keil C51 to SDCC.

The CH55x family of microcontrollers is notable because it has both an extremely low cost, USB device and host peripherals, and a preloaded USB bootloader.

Other Info

Contains tranlated comments for esier understanding how the ch55x range operate and extra examples included.

If you want a gentler introduction to CH55x programming, this Arduino port might be worth a look:

WCH has released official english translations of their datasheets for the parts:

Getting Started

Get the toolchain: Windows

You'll need a recent version of SDCC, as well as mingw for make, and likely also git-bash for the bash shell. Additionally, you'll need WCHISPTOOL to upload code to the chips.

TODO: How to set up the enviroment to find these bits automatically

Once the tools are installed, add the following lines to the end of your .bashrc file:

# SDCC compiler tools
export PATH=$PATH:/c/Program\ Files/SDCC/bin

# Mingw tools (for Make)
export PATH=$PATH:/c/Qt/Qt5.10.0/Tools/mingw530_32/bin

alias make=mingw32-make.exe

TODO: Use standalone mingw tools instead of the ones from Qt

Note: LibreCH551 works with the CH554, and can be used in place of the vendor-provided WCHISPTOOL on Windows. A big advantage of the open tools is that they can be automated, rather than manually clicking on things in the vendor tool. Please see the respective project pages for up-to-date installation instructions, as you'll likely need to bind the VID/PID pair for your specific WCH chip to the LibUSB using Zadig. Another tool is ch552tool.

Get the toolchain: Linux

For Debian-based systems, this should work:

sudo apt-install build-essential sdcc

There are multiple open source tools for loading firmware onto the CH55x chip:

These tools are reported to work with CH554 as well as CH552/CH551.

Get the toolchain: macOs

You'll need xcode (for make), as well as SDCC. ISP Tool will be same as Linux's.

Build the examples

Then clone this repository, and build the examples:

git clone
cd ch554_sdcc/examples

If everything is set up correctly, all of the examples should now be built.

On Windows: Use the 'WCHISPTool' to flash an image onto the target device. On Linux/Mac (or Windows after you have installed and configured LibreCH551), you can run 'make flash' to load the example onto your board.

Port a file from Keil C51 syntax to SDCC

The syntax for the two compilers are slightly incompatible. Notable issues from the SDK are:

  • SFR and SBIT defines are different
  • Absolute addressing format is different
  • SDCC doesn't automatically track absolute-addressed variables
  • SDCC can use standard types like 'uint8_t', the C51 examples used non-standard defines like 'UINT8'
  • SDCC is little endian, while C51 appears to be big endian

This project includes a simplistic python script that can automatically translate some simple grammer changes. It can be used like this:

python tools/ [source] [destination]

With any luck it should do 90% of the translation work for you.

Create a new example

Create a new directory in the examples folder, with the name of the new example:

cd examples/
mkdir fastblink
cd fastblink

Add a Makefile that referes to the master template makefile:

vi Makefile

With these contents:

TARGET = fastblink


include ../Makefile.include

Change the definition of target to match the new example name.

Next, add a barebones main file:

vi main.c

With these contents:

// Blink an LED connected to pin 1.7

#include <ch554.h>
#include <debug.h>

#define LED_PIN 7

void main() {

	// Configure pin 1.6 as GPIO output
	P1_DIR_PU &= 0x0C;
	P1_MOD_OC = P1_MOD_OC & ~(1<<LED_PIN);
	P1_DIR_PU = P1_DIR_PU |     (1<<LED_PIN);

	while (1) {
		LED = !LED;

And compile:


Oops! There is a problem:

$ make
sdcc -c -V -mmcs51 --model-small --xram-size 0x0400 --xram-loc 0x0000 --code-size 0x37FF -I../../include -DFREQ_SYS=12000000 main.c
+ /usr/bin/sdcpp -nostdinc -Wall -I../../include -DFREQ_SYS=12000000 -obj-ext=.rel -D__SDCC_MODEL_SMALL -D__SDCC_FLOAT_REENT -D__SDCC=3_5_0 -DSDCC=350 -D__SDCC_REVISION=9253 -D__SDCC_mcs51 -D__STDC_NO_COMPLEX__ -D__STDC_NO_THREADS__ -D__STDC_NO_ATOMICS__ -D__STDC_NO_VLA__ -isystem /usr/bin/../share/sdcc/include/mcs51 -isystem /usr/share/sdcc/include/mcs51 -isystem /usr/bin/../share/sdcc/include -isystem /usr/share/sdcc/include  main.c 
+ /usr/bin/sdas8051 -plosgffw main.rel main.asm
sdcc main.rel -V -mmcs51 --model-small --xram-size 0x0400 --xram-loc 0x0000 --code-size 0x37FF -I../../include -DFREQ_SYS=12000000 -o blink.ihx
+ /usr/bin/sdld -nf

?ASlink-Warning-Undefined Global '_CfgFsys' referenced by module 'main'

?ASlink-Warning-Undefined Global '_mDelaymS' referenced by module 'main'
+ /usr/bin/sdld -nf returned errorcode 512
../Makefile.include:38: recipe for target 'blink.ihx' failed
make: *** [blink.ihx] Error 1

Right, we forgot to add the debug.c source file to the Makefile. Update the Makefile so that it looks like this:

TARGET = fastblink

        main.c \

include ../Makefile.include

And re-run make. Everything should be fine:

$ make
sdcc -c -V -mmcs51 --model-small --xram-size 0x0400 --xram-loc 0x0000 --code-size 0x37FF -I../../include -DFREQ_SYS=12000000 ../../include/debug.c
+ /usr/bin/sdcpp -nostdinc -Wall -I../../include -DFREQ_SYS=12000000 -obj-ext=.rel -D__SDCC_MODEL_SMALL -D__SDCC_FLOAT_REENT -D__SDCC=3_5_0 -DSDCC=350 -D__SDCC_REVISION=9253 -D__SDCC_mcs51 -D__STDC_NO_COMPLEX__ -D__STDC_NO_THREADS__ -D__STDC_NO_ATOMICS__ -D__STDC_NO_VLA__ -isystem /usr/bin/../share/sdcc/include/mcs51 -isystem /usr/share/sdcc/include/mcs51 -isystem /usr/bin/../share/sdcc/include -isystem /usr/share/sdcc/include  ../../include/debug.c 
../../include/debug.c:225: warning 158: overflow in implicit constant conversion
+ /usr/bin/sdas8051 -plosgffw debug.rel debug.asm
sdcc main.rel debug.rel -V -mmcs51 --model-small --xram-size 0x0400 --xram-loc 0x0000 --code-size 0x37FF -I../../include -DFREQ_SYS=12000000 -o fastblink.ihx
+ /usr/bin/sdld -nf
packihx fastblink.ihx > fastblink.hex
packihx: read 31 lines, wrote 48: OK.

The .hex file can now be loaded onto the target using WCHISPTOOL.

Build configuration variables

The build configuration is specified in the master Makefile.include file, however some variables can be overridden by the local Makefile:

Makefile variable Description
TARGET Example name, used to name the .hex file
C_FILES List of c files to include in the example build
FREQ_SYS System clock frequency. Default is 12000000 (12MHz). See 'include/debug.c' for a list of accepted values
XRAM_SIZE Size of the non-reserved XRAM. Update to reserve a portion of the XRAM for absolute variables, such as for the USB DMA pointer
XRAM_LOC Starting position of the non-reserved XRAM. Update to reserve a portion of the XRAM for absolute variables, such as for the USB DMA pointer
STDIO_UART Set to '0' to use UART0 for STDIO, or '1' to use UART1 for STDIO (not finished)


Here is a list of the different peripheral drivers and examples that need to be ported

Peripheral Description Status
ADC Analog-to-digital converter in progress
DataFlash DataFlash (EEPROM) peripheral not started
GPIO I/O peripheral example not started
UART0/stdlib stdio example using UART0 in progress
UART1/stdlib stdio example using UART1 in progress
Watchdog Watchdog timer configuration not started
IAP Jump from user program to the bootloader complete
PWM Pulse Width modulation peripheral complete
SPI Serial Peripheral Interface not started
Timer 8051-style Timers 0 and 1 not started
Timer2 Extended Timer 2 not started
TouchKey Capacitive touch peripheral in progress
Chip ID Read the built-in chip ID not started
Type-C USB C power negotiation peripheral not started
USB\Device USB device peripheral: HID (?) profile not started
S_CDC USB device peripheral: CDC profile complete
U_DISK USB device peripheral: USB mass storage device profile not started
Compound_Dev USB device peripheral: compound device example (?) not started
USB\Host USB host peripheral: hub (?) example not started
USB\U_DISK USB host peripheral: read/write USB mass storage device not started


Contributions are welcome! Please see



CH554 software development kit for SDCC






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