Raspberry Pi

4B+

BCM2711 ARM Peripherals\
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711/rpi_DATA_2711_1p0_preliminary.pdf\
P. 178 (182) "Separate 32x8 transmit and 32x12 receive FIFO memory"\
HardwareSerialbuffer Default Tx 32x8bit Rx 32x12bit

BCM2835 ARM Peripherals\
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2835/BCM2835-ARM-Peripherals.pdf
P. 201 "Total Data FIFO RAM Depth 4096"
SoftwareSerialbuffer Default 4KB