From 9f7729ea3ce219c0e196f26ddf309008001e61d3 Mon Sep 17 00:00:00 2001 From: Aljoscha Vollmerhaus Date: Mon, 1 Sep 2025 15:02:06 +0200 Subject: [PATCH] BPI-R4: Add notes about GPON modules / 3.3V --- _sfp_cage/banana-pi.md | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/_sfp_cage/banana-pi.md b/_sfp_cage/banana-pi.md index 4586fb95..75c115c3 100644 --- a/_sfp_cage/banana-pi.md +++ b/_sfp_cage/banana-pi.md @@ -18,5 +18,17 @@ layout: default | SGMII | ✅ | ✅ | ✅ | | Type | Router | Router | Router | - +# Notes +## SFP power behavior on the Banana Pi R4 +Unlike some devices, the Banana Pi R4 does not apply 3.3 V to the SFP cage immediately when a module is inserted. +Instead, the board uses a load-switch MOSFET which only enables power once the module asserts the MOD_DEF0 pin (the presence/ID signal defined in the SFP specification). +This design can cause problems with “smart” GPON sticks such as the Zyxel PMG3000-D20B. +The stick’s internal SoC requires a long time to boot before, and only then it pulls MOD_DEF0 low. +Because the R4 waits for MOD_DEF0 before supplying power, the stick never receives power at all, resulting in a deadlock where the module stays unpowered. + +Some users in the BPI-R4 forums discussed a [workaround](https://forum.banana-pi.org/t/bpi-r4-zyxel-pmg3000-d20b-sfp-module-not-detected/18413/2) which bypasses the load-switch and feeds 3.3 V directly to the cage. +This allows modules like the PMG3000-D20B to start, but at the cost of losing proper hot-plug behavior. + +FS.com also offers GPON ONU sticks advertised as “with MAC,” which reportedly assert MOD_DEF0 early and may therefore avoid the issue without hardware modification. +However, evaluation of these modules on the R4 is still outstanding.