RP2040, i2c : wrong clock frequency #56230
Description
Describe the bug
SCL clock frequency generated do not correspond to DT clock-frequency definition:
&i2c1 {
status = "okay";
pinctrl-0 = < &i2c1_default >;
pinctrl-names = "default";
clock-frequency = <I2C_BITRATE_STANDARD>;
...
I2C_BITRATE_STANDARD is suppose to be 100kHz, but i measured 124kHz :
Which make a huge difference.
I investigate first using i2c logs and i found that hcnt and lcnt are wrong:
[00:00:00.005,000] <dbg> i2c_dw: i2c_dw_isr: I2C: interrupt received
[00:00:00.005,000] <dbg> i2c_dw: i2c_dw_setup: I2C: host configured as Master Device
[00:00:00.005,000] <dbg> i2c_dw: i2c_dw_setup: I2C: speed set to STANDARD
[00:00:00.005,000] <dbg> i2c_dw: i2c_dw_setup: I2C: lcnt = 500
[00:00:00.005,000] <dbg> i2c_dw: i2c_dw_setup: I2C: hcnt = 400
[00:00:00.005,000] <dbg> i2c_dw: i2c_dw_isr: I2C: interrupt received
Here is how lcnt and hcnt are defined :
#define I2C_STD_HCNT (CONFIG_I2C_DW_CLOCK_SPEED * 4)
#define I2C_STD_LCNT (CONFIG_I2C_DW_CLOCK_SPEED * 5)
Which is by default :
config I2C_DW_CLOCK_SPEED
default 100
The clock-frequency defined in device tree is not used by the driver.
Target: RP2040
To Reproduce
Can be reproduce with any program that use RP2040 as i2c controller and measure i2c frequency.
Expected behavior
clock-frequency property is used to compute SCL frequency.
Impact
Wrong scl signal frequency.
Environment (please complete the following information):
- OS: Ubuntu 22
- Toolchain Zephyr SDK
- Commit sha : 07c6af3
Additional context
Link of the conversation with @yonsch in discord for infos.