Enable full duplex I2S on STM32F405RG? Without MCK?

[bifurcation]

The STM32F405RG datasheet says that full duplex I2S is supported, but the I2S::new_full_duplex() method isn't enabled in Embassy. It looks like it is gated on the spi_v4 || spi_v5 config attributes, so maybe one of these is being set incorrectly for this chip? (Sorry, I wasn't able to figure out how these configs get set or I would have sent a PR!)

On a slightly different topic (and maybe a better issue for embassy_stm32), it seems like the mck output pin is not required for I2S rx/full_duplex operation, but it is required by the API. Is there a reason for this?

[Nybyte]

Greetings;

The problem is that the STM32F405RG supports full duplex I2S, but the Embassy configuration isn't enabling it properly. The spi_v4 and spi_v5 config attributes are set in the Embassy STM32 chip configuration files.

For the solution you need to:

You need to modify the Embassy STM32 configuration for the STM32F405. Here's what to do:

Locate the chip configuration file: In the embassy-stm32 repository, find the file for STM32F405 in embassy-stm32/src/chips/

Add the appropriate SPI version: The STM32F405 should have spi_v4 enabled. Add this to the chip's configuration:

// In the chip's config.rs or similar file impl embassy_stm32::peripherals::Config for Config { fn config() -> embassy_stm32::peripherals::Config { let mut config = embassy_stm32::peripherals::Config::default(); config.enable_spi_v4 = true; // Or set the appropriate SPI version config } }

Alternatively, submit a PR to fix the configuration: The proper fix would be to ensure the STM32F405 has the correct SPI version enabled in Embassy's chip definitions

[Dirbaio]

@Nybyte your suggestion makes no sense. Have you used AI to generate it?

[bifurcation]

@Dirbaio - Thanks for flagging that before I went off and tried to implement it :)

FWIW: I did do a little experiment with embassy_stm32 to see whether turning on one of these features would work. Enabling spi_v4 resulted in failures when building embassy_stm32 with -F stm32f405rg. With spi_v5 enabled, embassy_stm32 builds successfully, but my calling code still can't see I2S::new_full_duplex for some reason.

diff --git a/embassy-stm32/build.rs b/embassy-stm32/build.rs
index b5f1261..169444f 100644
--- a/embassy-stm32/build.rs
+++ b/embassy-stm32/build.rs
@@ -63,6 +63,10 @@ fn main() {
                 cfgs.enable(cfg_name);
             });
         }
+
+        // XXX(RLB) Manually enable spi_v5
+        cfgs.declare("spi_v5");
+        cfgs.declare("spi_v5_i2s");
     }
 
     for &(kind, versions) in ALL_PERIPHERAL_VERSIONS.iter() {
@@ -72,6 +76,10 @@ fn main() {
                 cfgs.declare(cfg_name);
             });
         }
+
+        // XXX(RLB) Manually enable spi_v5
+        cfgs.declare("spi_v5");
+        cfgs.declare("spi_v5_i2s");
     }
 
     // ========

[Nybyte]

@Dirbaio Sry english is not my mother languaje but I had same issue and I did what I posted there.

[bifurcation]

Taking a deeper look at this repo, it seems like this line in stm32-data-gen/src/perimap.rs might be the right place to make a change.

[bifurcation]

On further research, I am seeing that the spi_vX tags refer to different register sets (e.g., spi_v2_i2s vs spi_v5_i2s. Which means that simply enabling spi_vX for stm32f405rg is not going to be the right answer. Which means that this is an issue for embassy_stm32 and not this repo.

I filed embassy-rs/embassy#4698 to track the issue there.