I don't know how ST internal oscillator is implemented in silicon, but some MCUs have good internal oscillator.
For example the SAMD21 used on Arduino M0 board works fine with NSH running at 115200 and it even supports USB console, but I didn't test your freezing spray, maybe it could fail too. :-) This article compares crystal oscillator vs MEMS oscillator: https://www.avnet.com/wps/wcm/connect/onesite/9be4733b-3e9a-4880-8887-7d19ecf34a0e/quartz-crystal-vs-mems-oscillator.pdf The crystal oscillators are "crystal clear winner" (pun intended). I agree it is better to pay some cents to include a crystal in the board, but unfortunately the capitalism's pressure forces people to make mistakes. BR, Alan On 8/23/22, James Dougherty <jafr...@gmail.com> wrote: > 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 >> > >> >
