Hi all, I would like to be able to set a baud rate of 460800 for modem that we are testing. With the actual prescaler of 32 and a IPB frequency of 84MHz I got a 5.1% error (437500) vs a 0.9% error (456522) if I could use the prescaler of 4. See MPC5200B user manual page 15-46 for the calculation formula and page 15-12 for the CSR description.
Currently the code for the kernel we are using here, (2.6.29.2) seams not to take a prescaler of 4 into account. Line 249 of mpc52xx_uart.c http://lxr.linux.no/linux+v2.6.29.2/drivers/serial/mpc52xx_uart.c#L249 /* Search for bus-frequency property in this node or a parent */ static unsigned long mpc52xx_getuartclk(void *p) { /* * 5200 UARTs have a / 32 prescaler * but the generic serial code assumes 16 * so return ipb freq / 2 */ return mpc52xx_find_ipb_freq(p) / 2; } How could I make it use the prescaler of 4 without breaking anything that we currently have working ? I doubt that simply doing return mpc52xx_find_ipb_freq(p) / 4 would do the trick ...
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