Document the multifunction CH341 chip driver, in GPIO and I2C mode. Signed-off-by: frank zago <frank@xxxxxxxx> --- Documentation/misc-devices/ch341.rst | 109 +++++++++++++++++++++++++++ Documentation/misc-devices/index.rst | 1 + 2 files changed, 110 insertions(+) create mode 100644 Documentation/misc-devices/ch341.rst diff --git a/Documentation/misc-devices/ch341.rst b/Documentation/misc-devices/ch341.rst new file mode 100644 index 000000000000..65ba293bdc2d --- /dev/null +++ b/Documentation/misc-devices/ch341.rst @@ -0,0 +1,109 @@ +.. SPDX-License-Identifier: GPL-2.0-or-later + +=========================================================== +WinChipHead (沁恒) CH341 linux driver for I2C and GPIO mode +=========================================================== + +The CH341 is declined in several flavors, and may support one or more +of UART, SPI, I2C and GPIO, but not always simultaneously: + + - CH341 A/B/F: UART, Printer, SPI, I2C and GPIO + - CH341 C/T: UART and I2C + - CH341 H: SPI + +They work in 3 different modes, with only one being presented +depending on the USB PID: + + - 0x5523: UART mode, covered by the USB `ch341` serial driver + - 0x5512: SPI/I2C/GPIO mode, covered by the ch341 MFD drivers + - 0x5584: Parallel printer mode, covered by the USB `usblp` driver + +Mode selection is done at the hardware level by tying some +pins. Breakout boards with one of the CH341 chip usually have one or +more jumpers to select which mode they work on. At least one model +(CJMCU-341) appears to need bridging some solder pads to select a +different default. Breakout boards also don't usually offer an option +to configure the chip into printer mode; for that case, connect the +SCL and SDA lines directly together. + +The various CH341 appear to be indistinguishable from the +software. For instance the ch341 MFD driver will present a GPIO +interface for the CH341T although physical pins are not present, and +the device will accept GPIO commands. + +The ch341 MFD driver has been tested with a CH341A, CH341B and +CH341T. + +Some breakout boards work in 3.3V and 5V depending on some jumpers. + +The black chip programmer with a ZIF socket will power the CH341 at +3.3V if a jumper is set, but will only output 5V to the chips to be +programmed, which is not always desirable. A hardware hack to use 3.3V +everywhere, involving some soldering, is available at +https://eevblog.com/forum/repair/ch341a-serial-memory-programmer-power-supply-fix/ + +Some sample code for the CH341 is available at the manufacturer +website, at http://wch-ic.com/products/CH341.html + +The repository at https://github.com/boseji/CH341-Store contains a lot +of information on these chips, including datasheets. + +This driver is based on the pre-existing work at +https://github.com/gschorcht/i2c-ch341-usb + + +I2C Caveats +----------- + +The ch341 doesn't work with a Wii nunchuk, possibly because the +pull-up value is too low (1500 ohms). + +i2c AT24 eeproms can be read but not programmed properly because the +at24 linux driver tries to write a byte at a time, and doesn't wait at +all (or enough) between writes. Data corruption on writes does occur. + + +The GPIOs +--------- + +16 GPIOs are available on the CH341 A/B/F. The first 6 are input/output, +and the last 10 are input only. + +Pinout and their names as they appear on some breakout boards:: + + CH341A/B/F GPIO Names Mode + pin line + + 15 0 D0, CS0 input/output + 16 1 D1, CS1 input/output + 17 2 D2, CS2 input/output + 18 3 D3, SCK, DCK input/output + 19 4 D4, DOUT2, CS3 input/output + 20 5 D5, MOSI, DOUT, SDO input/output + 21 6 D6, DIN2 input + 22 7 D7, MISO, DIN input + 5 8 ERR input + 6 9 PEMP input + 7 10 INT input + 8 11 SLCT (SELECT) input + 26 12 RST# (?) input + 27 13 WT (WAIT) input + 4 14 DS (Data Select?) input + 3 15 AS (Address Select?) input + + +GPIO interrupt +~~~~~~~~~~~~~~ + +The INT pin, corresponding to GPIO 10 is an input pin that can trigger +an interrupt on a rising edge. Only that pin is able to generate an +interrupt, and only on a rising edge. Trying to monitor events on +another GPIO, or that GPIO on something other than a rising edge, will +be rejected. + + +SPI +--- + +This driver doesn't offer an SPI interface (yet) due to the +impossibility of declaring an SPI device like I2C does. diff --git a/Documentation/misc-devices/index.rst b/Documentation/misc-devices/index.rst index 756be15a49a4..e85531a4f354 100644 --- a/Documentation/misc-devices/index.rst +++ b/Documentation/misc-devices/index.rst @@ -19,6 +19,7 @@ fit into other categories. bh1770glc eeprom c2port + ch341 dw-xdata-pcie ibmvmc ics932s401 -- 2.32.0
