CV1800B Max Baud Rate

paul.effect · January 11, 2025, 2:05pm

Can anybody confirm the maximum baud rate of the UART peripheral of the CV1800B? The 64MB model.

Im still waiting on the board to be delivered and I’d very much like to prototype as much as possible before it gets here.

Thanks guys!

hatomist · January 14, 2025, 11:07pm

yo, I’ve successfully ran it at 1mbit baud on the DuoS from FreeRTOS side, but it requires some manual registry configuration to use a suitable clock source / dividers
Should also work for linux if driver is modified to use new clock dividers.

Stock max supported is likely 115200

github.com

zeroth-robotics/buildroot/blob/76050d75fb8ac5bc53cf8215d5b6b20f17e5a3a1/build/boards/cv181x/cv1813h_milkv_duos_emmc/u-boot/cvi_board_init.c#L57-L65


      
          	// UART dividers & uart0 fix
              // per 8.9.27 of sg2000_trm_en.pdf v1.01; setting UART* clock source to
              // disppll (1.188GHz) and dividing by 15 (to 79.2MHz)
              volatile uint32_t *reg_div_clk_cam0_200 = (volatile uint32_t *)0x030020a8;
              *reg_div_clk_cam0_200 = 0xF0109;
          
              // fix uboot logs, TODO: fix uboot dts and move clock init to appropriate place to avoid this bs
              volatile uint32_t *uart0_dll = (volatile uint32_t *)0x04140020;
              *uart0_dll = 43;

github.com

zeroth-robotics/buildroot/blob/76050d75fb8ac5bc53cf8215d5b6b20f17e5a3a1/freertos/cvitek/task/comm/src/riscv64/comm_main.c#L171-L197


      
          	// Initialize UART2
          	int baudrate = 1000000;
          	int uart_clock = 187500000;
          
          	// https://github.com/milkv-duo/duo-pinmux/blob/main/duos/func.h
          	// FMUX_GPIO_REG_IOCTRL_VIVO_CLK - B22, UART2_RX
          	// { "B227", "UART2_RX"}, => pin B22, func = 7
          	// FMUX_GPIO_REG_IOCTRL_VIVO_D6 - B15, UART2_TX
          	// { "B156", "UART2_TX"}, => pin B15, func = 6
          /*
          	[root@milkv-duo]~# devmem 0x03001160 32
          	0x00000007
          	[root@milkv-duo]~# devmem 0x03001144 32
          	0x00000006
          	[root@milkv-duo]~# devmem 0x03001C2C 32
          	0x00000048
          	[root@milkv-duo]~# devmem 0x03001C10 32
          	0x00000048
          */

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paul.effect · January 15, 2025, 7:52pm

I need to communicate at 1.5 - 2 Mbauds with a specific device (RS485, UART interface, can’t change this part) and Id really like, if possible, to not use a MCU just for SPI to UART ping - pong.

From what I read in the datasheet, the baud rate is calculated using the formula:

I suppose the “16” is the oversampling done by the peripheral, a reasonable assumption (I hope).

There’s also this:

It stands to reason 1500/N is a PLL output, where N can go from 8 up to… some value.

Now, I crunched the numbers and, in theory, I could reach 1875000 Bauds.

SCLK 150 Mhz: 10 N - 5 DLL >> 1875000 Bauds
SCLK 060 Mhz: 25 N - 2 DLL >> 1875000 Bauds
SCLK 030 Mhz: 50 N - 1 DLL >> 1875000 Bauds

I’m not even set on having the peripheral managed by the OS. If anything, I’d actually prefer the real time domain.

Thank you for your input, it was really helpful!