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Dual Port RAM on MPC8xx
- From: Will Wagner <will_wagner at carallon dot com>
- To: ecos-discuss at sources dot redhat dot com
- Date: Wed, 20 Apr 2005 11:38:17 +0100
- Subject: [ECOS] Dual Port RAM on MPC8xx
I'm trying to understand how the allocation of DPRAM is done in the
function _mpc8xx_allocBd in cpm.c.
Can someone explain why nextBD is initialised as:
static short *nextBd = (short *)(CYGHWR_HAL_VSR_TABLE + 0x1F0);
Presumably this is so that redboot and an application can cooperate when
using the DPRAM? Why is this address chosen and when is it's contents
ever initialised?
Presumably it may not have been initialised as in _mpc8xx_allocBd there
is this code:
if ((bd < QUICC_BD_BASE) || (bd > QUICC_BD_END)) {
// Most likely not set up - make a guess :-(
bd = *nextBd = QUICC_BD_BASE+0x400;
}
I guess this is starting 0x400 into the DPRAM so that an apllication
doesn't reuse any DPRAM used by redboot? Is this correct? I can find
where redboot ever initialises this memory so I can't see how it works.
Any help in understanding this is much appreciated.
Will Wagner
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