STM32U5 OSPI BusFault in memory mapped mode on unaligned writes
Good day,
I'm experiencing an unexplained bus fault when the MCU writes to unaligned (not aligned to 32-bit) addresses in the OSPI memory region. I've written a minimal implementation that shows where the issue occurs. See below.
I'm using the STM32U585 with two IS66WVS4M8BLL quad SPI modules. The OctoSPI peripheral is configured in Dual-Quad Mode. See the image for the settings as configured in STM32CubeMX. I use memory mapped mode. I've enabled DQS for writes as per 2.6.1 of the errata. I've tried different MPU cache configurations for this area: no MPU, MPU_DEVICE_nGnRnE, and (MPU_WRITE_THROUGH | MPU_NON_TRANSIENT | MPU_W_ALLOCATE | MPU_R_ALLOCATE).
Here's the minimal implementation. Note that 8-bit writes work if the previous write was aligned. See comments surrounded by ***, focussing on Test 2.
// Test 1: Unaligned 8-bit access
// *** This first test works without issues ***
volatile uint32_t sramByteLoopIndex;
volatile __IO uint8_t *mem_addr_byte;
volatile uint8_t sramTestValByte;
// Writing Sequence (8-bit, unaligned pattern)
mem_addr_byte = (uint8_t *)(OCTOSPI1_BASE);
for (sramByteLoopIndex = 0; sramByteLoopIndex < OSPI_MEM_SIZE_BYTES;
sramByteLoopIndex++)
{
sramTestValByte = (uint8_t)(sramByteLoopIndex &
0xFF); // Use lower 8 bits of index as pattern
*mem_addr_byte = sramTestValByte;
mem_addr_byte += 1;
}
// Reading Sequence (8-bit, unaligned check)
mem_addr_byte = (uint8_t *)(OCTOSPI1_BASE);
for (sramByteLoopIndex = 0; sramByteLoopIndex < OSPI_MEM_SIZE_BYTES;
sramByteLoopIndex++)
{
sramTestValByte = (uint8_t)(sramByteLoopIndex & 0xFF);
assert_param(*mem_addr_byte == sramTestValByte);
mem_addr_byte += 1;
}
// Test 2: Unaligned Copy within SRAM
// *** Here things are not well ***
volatile __IO uint8_t *src_addr_byte;
volatile __IO uint8_t *dst_addr_byte;
volatile uint8_t test_pattern_byte;
const uint32_t copy_size_bytes = 512; // Size of data to copy
// Ensure source and destination are unaligned and distinct
const uint32_t src_offset = 1; // Unaligned source start
const uint32_t dst_offset =
(OSPI_MEM_SIZE_BYTES / 2) + 3; // Unaligned destination start
// Ensure offsets are valid and don't cause wrap-around issues with copy size
if ((src_offset + copy_size_bytes < OSPI_MEM_SIZE_BYTES) &&
(dst_offset + copy_size_bytes < OSPI_MEM_SIZE_BYTES))
{
// Dummy aligned write first
// *** Removing this line causes BusFault on the write in code block 1 below ***
*((volatile __IO uint8_t *)OCTOSPI1_BASE) = 0;
// 1. Fill source region with a pattern
src_addr_byte = (uint8_t *)(OCTOSPI1_BASE + src_offset);
for (sramByteLoopIndex = 0; sramByteLoopIndex < copy_size_bytes;
sramByteLoopIndex++)
{
test_pattern_byte =
(uint8_t)((sramByteLoopIndex + 0xAA) & 0xFF); // Arbitrary pattern
*src_addr_byte = test_pattern_byte; // *** BusFault here on first iteration if the dummy write is commented out, otherwise no issues here ***
src_addr_byte++;
}
// 2. Perform byte-by-byte unaligned copy (Isolated Read/Write)
src_addr_byte = (uint8_t *)(OCTOSPI1_BASE + src_offset);
dst_addr_byte = (uint8_t *)(OCTOSPI1_BASE + dst_offset);
volatile uint8_t temp_byte; // Temporary variable
for (sramByteLoopIndex = 0; sramByteLoopIndex < copy_size_bytes;
sramByteLoopIndex++)
{
temp_byte = *src_addr_byte;
__asm__ __volatile__ ("nop"); // Tried adding NOP as per 2.6.10 of errata, even though we are not using DTR
*dst_addr_byte = temp_byte; // *** BusFault here on first iteration if the dummy aligned write is preset***
src_addr_byte++;
dst_addr_byte++;
}
// 3. Verify destination region
// *** We never get here ***
dst_addr_byte = (uint8_t *)(OCTOSPI1_BASE + dst_offset);
for (sramByteLoopIndex = 0; sramByteLoopIndex < copy_size_bytes;
sramByteLoopIndex++)
{
test_pattern_byte =
(uint8_t)((sramByteLoopIndex + 0xAA) & 0xFF); // Expected pattern
assert_param(*dst_addr_byte == test_pattern_byte);
dst_addr_byte++;
}
}I can post my memory mapped initialisation code, if needed.
Any suggestions of what I might be missing, or how to move forward?
@Alex - APMemory have you ever seen something like this?
