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rk27xx: don't switch SD cards to high-speed mode

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Every SD write failed. The card took the write command and went to
receive-data state, but never saw the block: CMD12 still found it there,
and the controller reported a missing CRC status after each block, 20
retries over. Reads worked. Stress-tested over USB mass storage on a
generic rk2705, with a SDHC card, in the normal firmware and in the
bootloader alike.

sd_init_card() switched the card to high-speed mode with CMD6. This host
is an SD 1.01 controller with a card clock of at most 25 MHz, per the
rk27xx datasheet; high speed and CMD6 came with SD 1.10, and a card
switched to it evidently does not take the data this host drives. The
original firmware never switches: after selecting the card it sets the
block length and a 1-bit bus and stays at default speed. A slower card
clock did not help; dropping the switch alone did.

Leave the card at default speed. Tested on a generic rk2705:
ums_stress.py over a 32 MiB window of the card - fill, verify, edge
sizes, a mixed read/write soak - passes at 2.3 MB/s writing and reading,
about 75% of what a 1-bit bus at 25 MHz carries.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Change-Id: Icfafab0bb460c8c0fda3dea455df9a36622bf764
This commit is contained in:
Marcin Bukat 2026-09-25 19:25:56 +02:00
parent 5c74d20bce
commit 2ce1cdcd8e
1 changed files with 5 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

9
firmware/target/arm/rk27xx/sd-rk27xx.c
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@ -323,10 +323,11 @@ static int sd_init_card(void)
if (!sd_wait_card_busy())
return -21;
/* CMD6 */
if(!send_cmd(SD_SWITCH_FUNC, 0x80fffff1, RES_R1, &response))
return -8;
sleep(HZ/10);
/* No CMD6 switch to high-speed mode: this is an SD 1.01 host, with a
* card clock of at most 25 MHz, and a card switched to high speed does
* not take the data it drives - every write failed, the card waiting in
* receive-data state for a block it never saw, while reads worked. The
* original firmware leaves the card at default speed too. */
/* Card back to full speed 25MHz*/
SD_CTRL = (SD_CTRL & ~0x7FF);