sd_font_render Directory Reference

Directory dependency graph for sd_font_render:

Directories
	src

Detailed Description

Loads a TTF/OTF font off an SD card and renders a paragraph of XHTML with reflow into the GLCDC framebuffer – the firmware promotion of the host test apps/shared_libs/reflow/tests/src/test_ra8_sdmmc_card_reflow.c, running the same SD -> ra8_fs -> reflow -> ra8_gfx -> GLCDC pipeline as a real RA8D2 binary.

The e-reader needs its fonts in storage rather than baked into flash, and #44 showed the on-board Octo-SPI part was not usable for that on this board, so font storage moved to the card. This app is the end-to-end proof the path works.

Any card works

SD bring-up and the font load go through the shared libs/ra8_sdfont helper, which self-provisions: if the card carries no font file, it writes a baked Latin-1 face and reads it back. So any FAT-formatted card just works, with no host-side image prep. ereader_ui uses the same helper read-only. On hardware that means a Digilent PMOD MicroSD in Pmod2 (J25) with any FAT card in it.

Reading a failure

The gate watches g_sfr_heartbeat, which the idle loop bumps only after a clean render – every failure stage parks instead, freezing it – so a steady advance proves the whole pipeline ran rather than that the firmware survived. When it does not advance, these are all SWD-readable:

• g_sfr_stage – bring-up progress, or a failure stage in the 0x80 range.
• g_sfr_err – the raw ra8_err_t from the font load.
• g_sfr_source – font read from the card, or self-provisioned this boot.
• g_sfr_font_len / g_sfr_pages / g_sfr_ink – font size, page count, inked pixels.

On failure the panel is also flooded a stage-coded gray, so a snapshot or a glance at the screen shows where it stopped.

Under the emulator this pipeline is genuinely slow: reading a font byte by byte over an emulated SPI bus and rasterising glyphs in software is nothing like the 1 GHz part, where it is instant. That is why the baked face is a compact Latin-1 subset – a full-size face can outrun the default run budget.