adding external memory to KLST_PANDA design … it s complicated

as it turns out there a more than one way to add external memory into a system. i have narrowed down my research to Octo-SPI and Flexible Memory Controller (FMC) interfaces.

FMC looks more like the traditional way of connecting external memory ICs. it is a more or less a parallel connecting of the memory IC to the MCU including all advantages and disadvantages of parallel connections: high speeds but also high number of pins. in contrast the Octo-SPI interface seems to be a bit more exclusive ( and in it s special variant HyperRAM™ even proprietary ). also the number of available memory ICs that implement Octo-SPI appears to be much lower than for FMC.

however, despite the potential better performance and the greater choice of memory ICs, i decided to opt for the HyperRAM™ way. the main reason being the lower demands in hardware resources. a few notes from my reseach and thinking process:

notes (20220714)

STM32H735G-DK uses two kinds of memory: FLASH and RAM both memories are interfaced via Octo-SPI and HyperRAM™ interfaces. note that STM32H743I-EVAL and STM32H753I-EVAL implements SDRAM memory via FMC interface.

for KLST audio applications FLASH memory is not suitable. therefore only the RAM version can be considered. however, suppliers are very short on memory ICs ( @JLCPCB there is literally no DRAM in stock ).

however, there are a few SDRAM chips in stock. however, however the FMC interface needs many more resources ( in case of STM32H743I-EVAL it requires 55 pins )! therefore i would stick with HyperRAM™ for now. PS ( DaisySeed seems to be using AS4C16M16SA SDRAM chip … which is currently available at JLCPCB ).

notes (20220716)

when the smoke has cleared i am left with an external RAM memory extension connected to an Octo-SPI/HyperRAM™ interface. some of the things i learned so far are:

  • connect external memory via Octo-SPI interface
  • STM32H73x MCU have 2 Octo-SPI interface but only one is available ( due to other peripherals )
  • try to use the IC specified by ST i.e S70KL1281DABHI023 ( 128Mb(=16MB), 3V3 ). there are quite a few subtle differences.
  • Octo-SPI RAM can be memory mapped and used ( almost ) like internal RAM ( e.g Octo-SPI1 > 0x900000000x9FFFFFFF i.e 0xFFFFFFF*4 = 1073741820bytes ≈ 1GB address space )
  • look into Master Direct Aemory Access controller (MDMA) + Memory Protection Unit (MPU)
  • Octo-SPI RAM can be used as frame buffer for LCDisplays
  • 16MB ( or 128Mb ) equal approx 90sec of audio data ( 32f ): (128Mb*1024*1024/8bits)/(48000Hz*1Channel*4bytes) ≈ 87,4sec
  • LCD framebuffer (RGB888) would require 225KB: 320*240*3/1024/1024 = 225KB ≈ 0.22MB
  • read Octo-SPI interface on STM32 microcontrollers (AN5050) + STM32H72x, … system architecture and performance (AN4891)

it is soooo important to test on STM32H735G-DK first. especially the combination of LCD and sound is crucial to be tested. also make sure to look into existing examples.

S70KL1281DABHI023 ordering part number deciphered

( see datasheet, p44 )

  • S70KL :: Device Family == 3.0V ( KS is for 1V8 )
  • 128 :: Density == 128MB
  • 1 :: Device Technology == 63nm
  • DA :: Speed == 100 MHz
  • B :: Package Type == 24-ball FBGA, 1.00 mm pitch
  • H :: Package Materials == Low-Halogen, Lead (Pb)-free
  • I :: Temperature Range == Industrial ( –40°C to +85°C )
  • 02 :: Model Number == Standard 6×8×1.0 mm package ( VAA024 )
  • 3 :: Packing Type == Tape and Reel


orthographical persepctive

what is the correct way of writing Octo-SPI anyway?

  • Octo-SPI
  • Octo SPI
  • OctoSPI
  • Octo-Spi

from what i am seeing in written documents in text Octo-SPI is the most common version and OCTOSPI is often used when to reference the actual hardware component.