A while ago AMD released AGESA 1.0.0.4 for most 400 and 500 series motherboards, but Series 300 lagged behind for multiple brands. The 1.0.0.4B BIOS firmware contains a truckload of new features and offered much better compatibility with for example DDR4 memory.

Historically AMD always has been very keen on supporting both old and new, I mean just look at their excellent socket support for example where you can purchase old and new Ryzen processors and place them on any 300, 400 or 500 series motherboard. So back to AGESA 1.0.0.4. There have been many BIOS updates available for all recent motherboards, however, Series 300 has been limping behind a bit for ASRock. ASRock, however, has submitted AGESA 1.0.0.4 Patch B revision firmware for the older X370, B350 and A320 the older chipsets X370 the last week or so. Interesting to see is that even the Z320 chipset based products also receive the newer 1.0.0.4 Patch B revision.

AGESA (AMD Generic Encapsulated System Architecture) version 1004 offered over 150 changes, this is a significant milestone release in the development of the AM4 platform. Among the updates:

• AGESA 1004 primarily focused on stability.
• This is the only AGESA validated and recommended for the AMD Ryzen 9 3950X. Your motherboard must have a BIOS with AGESA 1004 for full and proper support.
• It adds final support for "Eco Mode," accessible via Ryzen Master. Eco Mode brings AMD Configurable TDP (cTDP) technology to 3rd Gen Ryzen. With one button, you can run a 95W/105W model at 65W, or 65W models at 45W. This feature has been especially fun to use with the 3900X—12 cores at 65W! We know some of you have been very interested in a configuration like this, and now you can have it with the touch of a button. :)
• AGESA 1004 is the "big one" that reunites the codebase for all AM4-compatible processors. Up until now, 3rd Gen Ryzen has been a fork of the mainline. So, if you have an older Ryzen CPU and have been waiting for a major AGESA release: this is it! This will allow motherboard vendors to unify their CPU and chipset support lists on one codebase.
• As a major stability release, you're undoubtedly curious about the major changes. Here are some of the big ones:
• AMD X570 stability and compatibility with add-in devices.
• Improvements to interoperability of PCIe, USB, SATA, and device reset capabilities.
• Additional enhancements for PCIe device support and stability.
• Improved system stability when switching through ACPI power states.
• Improved POST/boot times. This will vary by motherboard.
• There are also two performance enhancements: improvements to the fastest core utilization, and further boost frequency optimizations for AMD Ryzen 9 3900X.

In summary, lots of goodness are available in AGESA 1004b and the Series 300 chipset seems to receive that update now pretty soon as well. We hope that other brands will follow as well.

Here's an example from the ASrock website on the X370 Taichi as an example:

Update AMD AGESA Combo-AM4 1.0.0.4 Patch B

*ASRock do NOT recommend updating this BIOS if Pinnacle, Raven, Summit or Bristol Ridge CPU is being used on your system.
*Before updating this BIOS, please also read the description in previous BIOS version.

MSI and Gigabyte already have updated most series 3000 BIOSes with an AGESA 1.0.0.4b update. ASUS still seems to offer 1.0.0.3ABBA for the bigger part. We didn't check all of them though. But if you own an ASRock Series 300 motherboard, this might be worth it to check out and update.