-----Original Message----- From: u-boot-users-admin@lists.sourceforge.net [mailto:u-boot-users-admin@lists.sourceforge.net]On Behalf Of Benjamin Collar Sent: Friday, September 24, 2004 7:55 AM To: ubootuser Subject: [U-Boot-Users] serial: polling or interrupt based?
Hi folks
I'm trying to set up the serial interface on my happy little board. Reading the CPU's manual (CPU is mpc852T), I'm at this section called SCC Initialization. I'm a bit confused, because the initialization procedure specifically says:
... 10. Write ones to SCCM register to enable interrupts 11. Write CICR to configure the SCC interrupt priority 12. Clear out any interrupts in CIPR 13. Write the CIMR to enable interrupts to the CPIC. ...
However, the u-boot code writes zeros to the SCCM and doesn't touch CIMR. So I guess it's polling based, yes?
Then the question is, do I simply skip steps 10-13? If I wanted to use interrupts instead of polling, what else would I need to change?
On a similar note, the manual for the MPC866, in appendix H which is specific for MPC852T, specifies that there is no BRG1 nor BRG2. The u-boot hard codes wiring BRG1 to the selected SCC. Why? Even more important: I have to obviously change it; is there more than one place I need to change (namely, replace cp_brgc1 with cp_brgc4)?
Thanks Ben
-- Benjamin Collar Siemens AG CT SE 2 Embedded Linux 089-636-53711
Well, either Wolfgang has used up his quota of answers for the week or my email is dropping incomming again :-/. Either way, here is an answer to your question on interrupts...
U-boot runs polled mode so yes, you should skip steps 10-13. U-boot is polling by design (simplicity). Adding interrupt handling to u-boot is unnecessary (in general) and undesirable.
Linux uses interrupts by design (obviously, it is necessary to do multitasking). The good news is, u-boot (polling) will very happily start up linux which then does all the device initialization, etc. to do interrupts. Support for the common peripherals should already exist for your CPU and board in linux.
I have not used the 8xx family so I cannot answer your BRG questions.
gvb
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