[#5789] Linux console does not work when SCLK is 27MHz

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[#5789] Linux console does not work when SCLK is 27MHz

Submitted By: Jie Zhang

Open Date

2009-12-23 22:56:18     Close Date

2009-12-24 03:35:07

Priority:

Medium     Assignee:

Sonic Zhang

Status:

Closed     Fixed In Release:

N/A

Found In Release:

snaps     Release:

Category:

N/A     Board:

STAMP

Processor:

BF533     Silicon Revision:

0.3

Is this bug repeatable?:

Yes     Resolution:

Rejected

Uboot version or rev.:

Latest trunk     Toolchain version or rev.:

Latest trunk

App binary format:

N/A     

Summary: Linux console does not work when SCLK is 27MHz

Details:

 

When setting SCLK to 27MHz in Linux kernel, Linux console prints not readable characters in minicom. If SCLK is 31MHz, everything is OK.

 

Follow-ups

 

--- Sonic Zhang                                              2009-12-23 23:49:35

Not a bug. The baudrate generated by blacfin is not exactly equal to standard

one. The errors depends on SCLK and the baudrate you expected.

 

SCLK = 27000000

BAUDRATE = 57600

Divisor = (SCLK + BAUDRATE*8)/(BAUDRATE*16) = (27145309 + 57600*8)/(57600*16) =

29

BAURATE = SCLK/(Divisor*16) = 27145309/(29*16) = 58520

errors = 58520 - 57600 = 980

 

SCLK = 31000000

BAUDRATE = 57600

Divisor = (SCLK + BAUDRATE*8)/(BAUDRATE*16) = (31166836 + 57600*8)/(57600*16) =

34

BAURATE = SCLK/(Divisor*16) = 31166836/(34*16) = 57291

errors = 57291 - 57600 = -309

 

In addition the crystal oscillator on blackfin board may have different errors

with that on your UART receiver board.

 

If it is larger than the tolerance of the UART receiver, characters received

are unreadable.

 

--- Jie Zhang                                                2009-12-24 03:35:09

Thanks!

 

 

 

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