There is an LED on the power supply and this begins flickering as soon as the chip boots into a program. Unfortunately I don't have access to a scope at the moment so I can't provide much more information than that.
If I hold the EN pin low and release, the serial output suggests the chip tries to boot and then the serial port drops communications. Serial output below
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// rst:0x1 (POWERON_RESET),boot:0x33 (SPI_FAST_FLASH_BOOT)
// configsip: 0, SPIWP:0xee
// clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
// mode:DIO, clock div:2
// load:0x3fff0030,len:4
// load:0x3fff0034,len:7168
// ho 0 tail 12 room 4
// load:0x40078000,len:14864
// load:0x40080400,len:4568
// entry 0x400806f0
I'm think the problem may be with the power supply struggling to power the chip through boot (could confirm with scope), or something I have missed with the strapping pins. Can anyone help to clear this up? Thanks in advance.