I'm trying to figure out whether the GPMC for the AM335x truly supports 8-bit external devices. The interface would be to an external FPGA.
According to SPRUH73C, section 7.1.3.1, 8-bit non-multiplexed devices are supported. Table 7-5 shows a pinmux option for it.
This is what concerns me:
From SPRUH73C:
7.1.3.3.8.2.2 Access Size Adaptation and Device Width
Each chip-select can be independently configured through the GPMC_CONFIG1_i[13-12] DEVICESIZE
field to interface with a 16-bit wide device or an 8-bit wide device. System requests with data width greater
than the external device data bus width are split into successive accesses according to both the external
device data-bus width and little-endian data organization.
The device does not provide the A0 byte address line required for random-byte addressable 8-bit wide
device interfacing (for both multiplexed and nonmultiplexed protocol). It limits the use of 8-bit wide device
interfacing to byte-alias accesses. This limitation is not applicable to NAND device interfacing (8-bit wide
or 16-bit wide devices).
This seems to contradict table 7-5. It's possible that I'm reading this wrong, or misinterpreting something, so it would be nice to check the words against a timing diagram showing 8-bit accesses to external memory. The only timing diagrams in the manual are for 16-bit external devices. As one could expect, A0 is not used.