Hi,
my "custom" bd_info structure (passed from my custom bootloader) looks as
following:
typedef struct bd_info {
unsigned long bi_memstart; /* start of DRAM memory */
unsigned long bi_memsize; /* size of DRAM memory in bytes */
unsigned long bi_flashstart; /* start of FLASH memory */
unsigned long bi_flashsize; /* size of FLASH memory */
unsigned long bi_flashoffset; /* reserved area for startup monitor
*/
unsigned long bi_sramstart; /* start of SRAM memory */
unsigned long bi_sramsize; /* size of SRAM memory */
unsigned long bi_immr_base; /* base of IMMR register */
unsigned long bi_bootflags; /* boot / reboot flag (for LynxOS)
*/
unsigned long bi_ip_addr; /* IP Address */
unsigned char bi_enetaddr[6]; /* Ethernet adress */
unsigned short bi_ethspeed; /* Ethernet speed in Mbps */
unsigned long bi_intfreq; /* Internal Freq, in MHz */
unsigned long bi_busfreq; /* Bus Freq, in MHz */
unsigned long bi_baudrate; /* Console Baudrate */
unsigned char bi_run_bank; /* Running Bank */
} bd_t;
My embed_config(bd_t **bdp) function (in
arch/ppc/boot/simple/embed_config.c)
does the following (using above structure) :
bd->bi_baudrate = 38400; /* changed from 115200 for debug - Alex */
bd->bi_memstart = 0;
bd->bi_memsize = (32 * 1024 * 1024);
bd->bi_intfreq = 50000000;
bd->bi_busfreq = 50000000;
Then we have, as Hans noted to me, the cpm_setbrg() function
(in arch/ppc/8xx_io/commproc.c):
/* Set a baud rate generator. This needs lots of work. There are
* four BRGs, any of which can be wired to any channel.
* The internal baud rate clock is the system clock divided by 16.
* This assumes the baudrate is 16x oversampled by the uart.
*/
#define BRG_INT_CLK (((bd_t *)__res)->bi_intfreq)
#define BRG_UART_CLK (BRG_INT_CLK/16)
#define BRG_UART_CLK_DIV16 (BRG_UART_CLK/16)
void
cpm_setbrg(uint brg, uint rate)
{
volatile uint *bp;
/* This is good enough to get SMCs running.....
*/
bp = (uint *)&cpmp->cp_brgc1;
bp += brg;
/* The BRG has a 12-bit counter. For really slow baud rates (or
* really fast processors), we may have to further divide by 16.
*/
if (((BRG_UART_CLK / rate) - 1) < 4096)
*bp = (((BRG_UART_CLK / rate) - 1) << 1) | CPM_BRG_EN;
else
*bp = (((BRG_UART_CLK_DIV16 / rate) - 1) << 1) |
CPM_BRG_EN | CPM_BRG_DIV16;
}
So what could go wrong here in terms of setting the baudrate for the serial
uart
(which "presumably" causes printing 3 good characters and then garbage
during kernel booting) ?
