Programming Mimosa chips
Overview
The system uses a C progarm named xsvfPlayer to read in JTAG configurations from an xsvf format binary file, and set up the JTAG pins to configure the front-end Mimosa chips. The xsvf binary file is generated from a readable text format svf file with Xilinx SVF-to-XSVF Writer - svf2xsvf.
In our system, we need to configure about 100 mimosa chips with different threshold voltages and other settings, sometime we also need to change these values online, it's not practical to generate a xsvf file for every chip. Instead, it's possible to have a template xsvf file and hack into this file to modify the corresponded byte values for every chip. So we need to know some fundamental informations of the xsvf file.
Multi-device JTAG chain
Normally when we want to access one of the devices in the JTAG chain with more than one device, we need to bypass all the others. When those devices are bypassed, they just connect their 1-bit bypass registers into the JTAG chain, it looks as belwo for the 1st chip in a 4-chip JTAG chain:
_______chip1________ _2_ _3_ _4_
TDI --> |0|1|..........|127| --> |0| -> |0| -> |0| -> TDO
-------------------- --- --- ---
The JTAG bypass command is the one with all 1s for all command bits, and normally we can write zeros to the bypass registers.