CH341A USB to SPI and GPIO Linux kernel driver
CH341A USB to SPI and GPIO Linux part driver
The driver can be utilized with CH341A USB to UART/I2C/SPI connector sheets to interface SPI captives to a Linux have. It utilizes either the quick SPI equipment interface which is, notwithstanding, restricted to SPI mode 0 or a sluggish SPI bit banging execution.
Moreover, CH341A information sticks that are not utilized for the SPI point of interaction can be arranged as GPIO pins. The driver can create programming hinders for all information pins. One info pin can be associated with the CH341A intrude on pin to create equipment interferes. Nonetheless, since USB is an offbeat correspondence framework, ensuring accurate timings for GPIOs and interrupts is absurd.
Constraints of the SPI interface
The SPI equipment interface execution is restricted to
SPI mode 0 (CPOL=0, CPHA=0)
fixed clock recurrence of around 1.4 MHz,
low dynamic CS signal,
single piece moves,
8 pieces for each word, and
3 slaves at most extreme.
In view of the extremely restricted documentation and applications that are practically all in Chinese, it is difficult to sort out whether these boundaries can be changed through control orders. Subsequently you need to live with this arrangement for what it’s worth to utilize the equipment execution :- (
The piece banging execution permits the accompanying SPI modes
SPI mode 1 (CPOL=0, CPHA=1)
SPI mode 2 (CPOL=0, CPHA=1)
SPI mode 3 (CPOL=0, CPHA=1)
as well as high dynamic CS signals. It is exceptionally sluggish. Just a SCK clock recurrence of around 400 kHz can be reached, so one byte takes around 14 us. Nonetheless, every byte of a message must be sent as a different USB message to the connector in light of its bitwise execution and the extremely restricted USB endpoint support sizes. This outcomes into a deferral of around 6.5 ms between every byte. Moreover, dealing with the CS signal before the exchange and after the exchange creates an unexpected setback of around 20 ms. Consequently, it takes about
20 ms + n * 0.014 ms + (n-1) * 6.5 ms
to move a message of n bytes.
The two executions permit the transmission with MSB first (SPI_MSB_FIRST) and LSB first (SPI_LSB_FIRST).
SPI setup
The driver uses following CH341A pins for the SPI interface.
| Pin | Name | Direction | Function SPI (CH341A) |
|---|---|---|---|
| 18 | D3 | output | SCK (DCK) |
| 20 | D5 | output | MOSI (DOUT) |
| 22 | D7 | input | MISO (DIN) |
| 15 | D0 | output | CS0 |
| 16 | D1 | output | CS1 |
| 17 | D2 | output | CS2 |
GPIO configuration
Five of the data pins can be configured as GPIO pins if they are not used for the SPI interface or as chip select signals:
| Pin | Name | SPI Function (default) | Configurable as (CH341 default in bold face) |
|---|---|---|---|
| 15 | D0 | CS0 | Input, Output, CS |
| 16 | D1 | CS1 | Input, Output, CS |
| 17 | D2 | CS2 | Input, Output, CS |
| 19 | D4 | OUT2 | Input, Output |
| 21 | D6 | IN2 | Input |
Please note:
- Direction of pins that are configured as input or output can be changed during runtime.
- Pin 21 (D6/IN2) can only be configured as input. It’s direction can’t be changed during runtime.
- At least one of the CS data pins D0…D2 has to be configured as CS signal.
- One of the inputs can be configured to generate hardware interrupts for rising edges of signals. For that purpose, the pin has to be connected with the CH341A INT pin 7.
Installation of the driver
Prerequisites
To compile the driver, you must have installed current kernel header files.
Even though it is not mandatory, it is highly recommended to use DKMS (dynamic kernel module support) for the installation of the driver. DKMS allows to manage kernel modules whose sources reside outside the kernel source tree. Such modules are then automatically rebuilt when a new kernel version is installed.
To use DKMS, it has to be installed before, e.g., with command
