Hi David, Wow. That is precisely what is wrong, you can get yourself a little TRIM and make one of the boards work, but then you would have to hand tune them +/- 1% for every baud rate and worse, temperatures. So better to pay the 71 cents and put the 8M crystal on the board. For testing I used cold spray and different baud rates to see that it is much worse, probably more like 2% on the megabaud rates. APB1 can't go over 36Mhz or the backplane hangs. PS, the other app note is on 8Mhz HSI and link is here https://www.st.com/resource/en/application_note/an2868-stm32f10xxx-internal-rc-oscillator-hsi-calibration-stmicroelectronics.pdf
Anyhow, the summary is one may use the HSI for bringup and get NSH on /dev/ttyS0 as /dev/console but for real comms and especially megabaud you need external resonator or crystal and HSE enabled as per default in stmf103-minimum Thank you. -James On Mon, Aug 22, 2022 at 11:55 PM David Sidrane <david.sidr...@nscdg.com> wrote: > HSI is not a good choice if there are external interfaces. It can vary too > much part to part and over temperature to meet the 2% across the system > boundary. They claim 1% @25c but that is 1/2 the budget to begin with, > > > https://www.st.com/resource/en/application_note/dm00425536-how-to-optimize-stm32-mcus-internal-rc-oscillator-accuracy-stmicroelectronics.pdf > > > > > On Tue, Aug 23, 2022 at 2:10 AM James Dougherty <jafr...@gmail.com> wrote: > > > Anyone ever use the HSI on STM32F103, how about RET6? I know the code is > > set up for HSE. I got it working, at least UART1. > > But now, the other usart devices ... Wondering if anyone has ever run > into > > UART baud rate mismatches on using HSI? I have a few > > radios that work great with an existing driver and a diff design, but not > > joy on the F103RET6. I am using internal PLL, x8 (64Mhz) > > and 32Mhz (APB1, APB2) if anyone has any debug pointers that would be > > great. Its weird, the UART1 uses APB2, and others > > use APB1. I know I need the external crystal but I got these boards and > no > > clock stuffed... (sigh) > > > > thanks! > > -james > > >
