Why single .grd NDVI file from processLandsatBatch

[sak-geo]

Hi there, I am very new to programming and time series analysis. On a pilot basis, I am running processLandsatBatch for 8 Landsat7 images acquired over different years with the following code:

processLandsatBatch(x=dir, pattern = glob2rx('*.zip'), outdir = dirout, srdir = srdir, delete=TRUE, vi='ndvi', mask='pixel_qa', keep=0, overwrite=TRUE)

and, it returns with a single file: ndvi.NA.grd
If I try overwrite=FALSE it returns the following error:

Error in .startRasterWriting(out, filename, format = filetype, ...) :
Pilot/ndvi.NA.grd exists. use 'overwrite=TRUE' if you want to overwrite it

And even the ndvi produced has NA values! Can anybody tell me what's wrong here?

[sak-geo]

@loicdtx can you help, please.