[CPU-3.3] When the CPU Accesses Peripherals and Writes a Single Address Repeatedly, Some Writes May Be Lost

Affected revisions: v0.0

Description

Some ESP32 peripherals are mapped to two internal memory buses (AHB & DPORT). When written via DPORT, consecutive writes to the same address may be lost.

Workarounds

When writing the same register address (i.e., FIFO-like addresses) in sequential instructions, use the equivalent AHB address not the DPORT address. (For other kinds of register writes, using DPORT registers will give better write performance.)

Registers	DPORT Addresses	AHB (Safe) Addresses
UART_FIFO_REG	0x3FF40000	0x60000000
UART1_FIFO_REG	0x3FF50000	0x60010000
UART2_FIFO_REG	0x3FF6E000	0x6002E000
I2S0_FIFO_RD_REG	0x3FF4F004	0x6000F004
I2S1_FIFO_RD_REG	0x3FF6D004	0x6002D004
GPIO_OUT_REG	0x3FF44004	0x60004004
GPIO_OUT_W1TS_REG	0x3FF44008	0x60004008
GPIO_OUT_W1TC_REG	0x3FF4400C	0x6000400C
GPIO_OUT1_REG	0x3FF44010	0x60004010
GPIO_OUT1_W1TS_REG	0x3FF44014	0x60004014
GPIO_OUT1_W1TC_REG	0x3FF44018	0x60004018
GPIO_ENABLE_REG	0x3FF44020	0x60004020
GPIO_ENABLE_W1TS_REG	0x3FF44024	0x60004024
GPIO_ENABLE_W1TC_REG	0x3FF44028	0x60004028
GPIO_ENABLE1_REG	0x3FF4402C	0x6000402C
GPIO_ENABLE1_W1TS_REG	0x3FF44030	0x60004030
GPIO_ENABLE1_W1TC_REG	0x3FF44034	0x60004034

Solution

Fixed in chip revision v1.0.

Note

Software cannot use AHB addresses to read FIFO.