On 23/06/20 22:07, Eric Blake wrote: >> >> uint64_t baud = ((value & UART_CTRL_NCO) >> 16); >> baud *= 1000; >> - baud /= 2 ^ 20; >> + baud >>= 20; > > Dividing by 1M instead of 22 seems much more logical, indeed :)
Based on the spec, the "* 1000" is the clock, in other words this is a fixed point value relative to the clock: f_baud = NCO * f_clock / 2^20 The example in the spec (https://docs.opentitan.org/hw/ip/uart/doc/) has f_clock = 50 MHz, while here it's only 1 kHz. And the register is only 16 bit, so the above would only allow a baud rate up to 62 (65535 * 1000 / 2^20). Should the clock be a property of the device instead? Thanks, Paolo > It's odd that we are scaling up by 1000, down by 1024*1024, then > >> s->char_tx_time = (NANOSECONDS_PER_SECOND / baud) * 10;
