On Monday, September 19, 2011 21:07:48 Graeme Russ wrote:
a) Use a particular serial driver directly - perfect if you have only one serial port (or don't care about the others)
yes. this is what we have today with !SERIAL_MULTI. every serial driver implements serial_{init,puts,putc,tstc,getc,setbrg,set_baud}. this code works for exactly one device and is extremely thin. in the case of Blackfin UARTs, serial_putc() does two things: wait for the hardware FIFO to free up, and then writes the char to the hardware registers. serial_tstc() is a bit test of a single hardware status register read. you really can't get any simpler than this.
b) Use the SERIAL_MULTI 'management layer' and 'register' each relavent serial port on the board. The board will need to define a (probably hard-coded) a default to handle I/O until the environment can be read and the hardware initialised to actually make the serial ports operational.
atm, SERIAL_MULTI provides support for "early" output by means of the default_serial_console() function. but even this requires going through the .data section in order to lookup the func pointer to the device pointers. which means i dont think it works for the ports which do relocation on the fly. but i dont know as i havent worked at that level with the relevant arches before.
So in theory, we should be able to register an arbitrary number of serial ports, each with potentially different hardware and therefore different drivers.
this works today
The board (or SoC) init function should be able to simply call serial_register() for each serial port with a name and info into how to talk to the hardware (hardware type, base address etc).
this is doable today, but the standard is to add all devices to common/serial.c:serial_initialize()
The SERIAL_MULTI framework should then simply manage the list of serial devices and redirect I/O based on environment settings
which is what it does
one limitation of the current serial/stdio framework is that the serial multi core can only have one active device at a time. the stdio core can have one per channel: stdin, stderr, stdout. so this reminds me of the other goal: merge serial framework into stdio framework. -mike