Tapir Player

[davidzweig]

Hello. I used to use Rockbox a lot on a Sansa Clip. For some time, I've been working on a design for a kind of remote that connects with an Android smartphone over a BLE connection to allow control of a special audio player for studying languages. It would be an extension of the Language Reactor project. We're a few developers who usually make web software, but we're working with a couple of other companies for the electronic and mechanical design/manufacture.

I revisited the project this year. There's this SoC, planned for use in the upcoming Pebble Core Time 2: https://www.cnx-software.com/2025/05/14/sifli-sf32lb52j-big-little-arm-cortex-m33-bluetooth-mcu-powers-the-core-time-2-smartwatch/

Some interesting features:

Arm Cortex-M33 STAR-MC1 core @ up to 240MHz
512KB SRAM, 16MB PSRAM
BT Classic + BLE
Open development materials / SDK

Smartwatch-format IPS displays are something like $1.50–$1.80.

The SF32LB52J has a mono audio DAC, but we could add, say, a TLV320DAC3100 with a 3.5mm jack.
Another slight downside is that USB support is only 'full speed' (12 Mbit/s)... maybe we could add a USB-to-SD card bridge chip.

Our previous remote design, based on the nRF52, is on the left, and the new concept is on the right. 12 buttons on the front, individually lit with color LEDs, with some additional edge buttons:

https://postimg.cc/d7QvgM1y

We're starting schematic design with the SiFli chip and, if everything goes smoothly, looking at manufacturing a device later in the year, with a retail price around 25–30 EUR. The schematic will be published online.

There is quite a nice-looking third-party smartwatch-format development board: https://item.taobao.com/item.htm?id=938017721882 . I ordered 10 units via Superbuy purchase agent last night to Bulgaria. I can forward a couple within Europe if someone is interested.

Anyway, I thought I would check in here to see if there were any comments on the suitability of the hardware for Rockbox.

[speachy]

Arm Cortex-M33 STAR-MC1 core @ up to 240MHz
512KB SRAM, 16MB PSRAM
BT Classic + BLE
Open development materials / SDK

The SF32LB52J has a mono audio DAC, but we could add, say, a TLV320DAC3100 with a 3.5mm jack.
Another slight downside is that USB support is only 'full speed' (12 Mbit/s)... maybe we could add a USB-to-SD card bridge chip.

The CPU core is a little slower than I'd like to see but it'll easily handle any reasonable audio format.   The main strike against it is the need for PSRAM, however the SoC supports running it at 8bit 144MHz DDR, which is a lot faster than one typically sees -- the PSRAM is on-package too! With respect to the slow USB interface, as long as the SD card is removeable, it's not a big deal in practice -- and adding a USB2<->SD bridge wil not be cost (both in $$ and footprint) effective.

Also, the SG32LB52x reference manual shows the DAC can drive 16-bit stereo output (section 11.3.4.2) to either the internal codec or via I2S, at a 48KHz maximum sample rate.  There's conflicting language about the ability to drive 24bit stereo signals; playing back two 24-bit mono signals is supported, though you may have to handle the data buffers for each independently?  The I2S peripheral supports stereo 24-bit, though it's not immediately clear if it can be handed data via DMA directly or has to go through the "AudPRC" block.

So in short, this looks like it would work for Rockbox.

Oh, with regards to the SDK; it looks like it has a complete set of CMSIS headers and the misc driver (etc) code will be a good reference (and may even be usable as-is..)

I wonder if the bluetooth stack is available in source form...

EDIT:  It uses a modified version the Zephyr host stack + profiles in source form, but still uses a binary blob (presumably for the controller stack).  A2DP is there but surprisingly, no AVRCP?  (I wonder how hard it would be to drag this as-is into rockbox, to use with the native ErosQ port...)

[davidzweig]

Thank you for your thoughtful response.  Yes I think you are right about the DAC.

We'll probably use the SF32LB52-ULP schematic as a starting point, it's likely already cost-optimised.

https://oshwhub.com/li-chuang-kai-fa-ban/li-chuang-huang-shan-pai-sf32lb52-kai-fa-ban-v1-2

I'll post a schematic here when there's an initial design. The device should be easy to flash and debug.

PMed you.

[speachy]

Thank you for your thoughtful response.  Yes I think you are right about the DAC.

We'll probably use the SF32LB52-ULP schematic as a starting point, it's likely already cost-optimised.

https://oshwhub.com/li-chuang-kai-fa-ban/li-chuang-huang-shan-pai-sf32lb52-kai-fa-ban-v1-2

I'll post a schematic here when there's an initial design. The device should be easy to flash and debug.

BTW, I wrote up a "rockbox wishlist" some time ago, just some stuff to consider when putting together a schematic:   https://www.shaftnet.org/~pizza/rb-wishlist.txt