I am using PPC 405GP rev E, 200MHz cpu clock. The desired baudrate of UART is 9600.
According to the manual, developer needs to decide a devisor udiv to get the serial clock, i.e. serial clock = cpu clock / udiv
An UART baudrate divisior bdiv is defined as bdiv = serial clock / (desired baudrate * 16)
I checked the u-boot source code and got a couple of questions:
1. a CFG_BASE_BAUD is defined upfront in u-boot. What is this? Is CFG_BASE_BAUD = serial clock / 16? If so the serial clock is fixed, instead of programmable, is that right? But the manual says the serial clock is programmable through setting the value of udiv. So udiv and the serial clock, which should be set first? In another word, should udiv be decided by user and then cpu calculate the serial clock according to udiv, or should user put a fixed serial clock to let cpu calculate udiv?
2. With two parameters, i.e. cpu clock = 200MHz and UART baudrate = 9600, can program decide all divisors such as udiv and bdiv? I found a table in a vxworks boot rom source, which tells developers when clock = 200M, UART baudrate = 9600, the udiv should be set as 14. How this number comes from? Or is it just a suggested number?
Thanks!
Frank
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