BCM2835 LoSSI Clock Output
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
- Issue type
- Bug
- Clarity
- Clearly specified
- Activity status
- Stale
- Tech stack
- c, linux
- Domain
- embedded-iot, operating-systems
Research direction
Start in bcm2835_spi_transfer_one() and reproduce the LoSSI transfer with SPI_MODE_3, SPI_3WIRE, and BCM2835_SPI_CS_LEN enabled. Compare the controller's measured output with the BCM2835 ARM Peripherals specification. Done means a one-byte transfer produces 9 clock cycles rather than 10 on the Raspberry Pi CM3+ setup.
Written by the indexing model from the issue text.
Description
Describe the bug
I know the Linux Kernel does not natively support LoSSI (this is something I am working on).
However the BCM2835 SPI Driver in LoSSI Mode outputs 10 clock cycles instead of 9 clock cycles as indicated by the BCM2835 ARM Peripherals spec.
To reproduce
Add code to enable LoSSI in function bcm2835_spi_transfer_one() and send one byte of data.
cs |= BCM2835_SPI_CS_LEN;
Note: SPI Mode is set to SPI_MODE_3 and SPI_3WIRE
Expected behaviour
Expect 9 clock cycles
Actual behaviour
Measured 10 clock cycles
System
Raspberry Pi CM3+ w/ IO Board
Kernel Version: v5.3.7-yocto-standard
Firmware Date: Aug 22 2019 14:00:42
Firmware Version: 0e6daa5106dd4164474616408e0dc24f997ffcf3 (clean) (release) (start_x)
- Dominant language
- C
- Stars
- 13.2k
- Forks
- 5.5k
- Avg merge
- 2d 21h
- Merged PRs (30d)
- 21
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