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complete config_machineinit() with "seems ok" early initialization code:
- disable watchdog
- configure main oscillator and PLL through PMC
- enable USART0 (presume in programmed I/O mode for now)

this all is untested (and even stupid), first thing to do is to check
if we really will run at 96 MHz after PMC reprogramming...

/*
 * $Id: config.c,v 1.5 2007/11/13 22:40:33 nbrk Exp $
 */
#include <sys/types.h>
#include <sys/device.h>

/* devices' regs that we will touch in config_machineinit() */ 
#include <arch/sam7s64/dev/sapmcreg.h>
#include <arch/sam7s64/dev/sawdtreg.h>
#include <arch/sam7s64/dev/sapioreg.h>
#include <arch/sam7s64/dev/sausartreg.h>

/*
 * Configuration file for platform (AT91SAM7S64).
 */

/* device drivers */
extern struct driver root_dr;
extern struct driver cpu_dr;
extern struct driver saapbus_dr;


extern void(*putchar)(char);
void 	sauart_early_putc(char ch);

/* amount of physical memory, in Bytes */
uint32_t physmem = 16384 /* 16KB :) */;

/*
 * Where to attach each device.
 */
struct attachinfo config_attachinfo[] = {
	/* child,   parent, pminor, loc, 	intrno, flags */
	{ "cpu" , 	"root", 	0, 0, 			0,	0 },
	{ "saapbus","root", 	0, 0, 			0,	0 },
	{ NULL, 	NULL, 		0, 0, 			0,  0 }
};


/*
 * Link device names with their drivers.
 */
struct driverinfo config_driverinfo[] = {
/* name, driverp, ninstances (should be -1) */
	{ "root", &root_dr, -1 },
	{ "cpu" , &cpu_dr, -1 },
	{ "saapbus" , &saapbus_dr, -1 },
	{ NULL, NULL, 0 }
};


/*
 * Machine early-stage initialization hooks.
 */

void
config_machineinit(void)
{
	/*
	 * Initialize critical devices at startup.
	 */

	/* XXX kill all magic here */

	/* disable watchdog */
	*(uint32_t)(SAWDT_BASE + SAWDT_WDT_MR) |= 0x00001000 /* WDDIS */;

	/* "Start up time = 8 * OSCOUNT / SLCK" (slow clock cycles) */
	(uint32_t)(SAPMC_BASE + SAPMC_CKGR_MOR) = 0x00000701;
	/* wait main osc. to stabilize.. */
	while (! *(uint32_t)(SAPMC_BASE + SAPMC_PMC_SR) & 0x00000001 )
		;

	/* set PLL */
	*(uint32_t)(SAPMC_BASE + SAPMC_CKGR_PLLR) = 0x00040805;
	/* wait.. */
	while(! *(uint32_t)(SAPMC_BASE + SAPMC_PMC_SR) & 0x00000004)
		;
	while(! *(uint32_t)(SAPMC_BASE + SAPMC_PMC_SR) & 0x00000008 /* MCKRDY */)
		;

	/* select Master Clock and Processor Clock; select (PLL clock / 2) */
	*(uint32_t)(SAPMC_BASE + SAPMC_PMC_MCKR) = 0x00000003 /* PLL in CSS */ | 0x00000004 /* presc. = 2 */;
	/* wait.. */
	while(! *(uint32_t)(SAPMC_BASE + SAPMC_PMC_SR) & 0x00000008)
		;

	/*
	 * Initialize USART0.
	 */
	/* disable PIO from controlling RXD0/TXD0 pins (USART0 at Periph. A) */
	*(uint32_t)(SAPIO_BASE + SAPIO_PIO_PDR) = 0x00000030 /* PIN5 | PIN6 */
	/* select this pins in Peripheral A */
	*(uint32_t)(SAPIO_BASE + SAPIO_PIO_ASR) = 0x00000030 /* now, RXD0 | TXD0 */

	/* enable clock to USART0 */
	*(uint32_t)(SAPMC_BASE + SAPMC_PMC_PCER) = 0x00000006 /* 6 is ID of USART0 */

	/* set baud rate */
	*(uint32_t)(SAUSART_0_BASE + SAUSART_US_BRGR) = 313 /* XXX (48000000 / 9600 * 16) */

	/* select usart mode */
	*(uint32_t)(SAUSART_0_BASE + SAUSART_US_MR) = 0x000008c0 /* XXX eleminate magic */

	/* TODO enable DMA transfers for TX/RX in PDC */

	/* enable transmitter/receiver */
	*(uint32_t)(SAUSART_0_BASE + SAUSART_US_CR) = 0x00000050 /* TXEN | RXEN */

	/* TODO redefine putchar */
	//putchar = sausart_0_putchar;
}